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2023-07 July Science Readings

Well, I didn't do damned-all last month. Other things.

There seems to be a lot of work on stellar dimmings going on at the moment.

Articles studied this July- some of which might go to Slashdot.

A first great dimming.Betelgeuse Misbehaviour

Beware of Hubris : World Is Not Enough - WINE

Discovery of Gaia17bpp, a Giant Star with The Deepest and Longest Known [Stellar] Dimming Event

Astrophysics observatories as seismographs

Great Dimming But RW Cephei, not Betelgeuse

Potential Supernova Candidates

Exponential distance relation (aka Titius-Bode "Law") in extra solar planetary systems

End of document

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Betelgeuse Misbehaviour

The evolutionary stage of Betelgeuse inferred from its pulsation periods

(Further discussion from Molńar, Meridith and Leung appended to original article.)

About a year ago, I posted on the unusual behaviour (misbehaviour, even) of Betelgeuse over the last few years, with the "Great Dimming" superimposed on it's semi-regular brightness variations. My "laughing price" thesis was that by extreme extrapolation of diameter estimates for the star, one could "predict" [sic, my tyops] simplistically, the expected "zero diameter [tyop, "] date range for Betelgeuse is 2030 to about 2040. That was from a 2009 paper, well before the "Great Dimming". Totally unreasonable from any statistical point of view, and I knew it as I calculated it.

So, another paper has come out, also pointing in the same sort of date range, but predicting a supernova not a disappearence up the stellar jacksy. Meh, I can live with that. They've probably approached the question more seriously than I did.

These authors are using a slightly more realistic stellar model than mine, and also new interpretations of old data which suggest (Neuhäuser R., Torres G., et al, 2022, MNRAS, 516, 693) that in the pre-instrumental period, Betelgeuse was yellower (and so, hotter) then than it is today. They put this - the colour change ; the semi-periodic pulsations - together to come up with a revised model for Betelgeuses fundamental parameters thar are a bit different to generally accepted models, but not wildly so. And which, these authors suggest, means that Betelgeuse is teetering on the point of experiencing a core collapse supernova in the imminent future - within a few tens of years.

Well, that'd be fun, for almost everybody. An end most devoutly to be hoped for. And on an "I told you so, young whipper-snapper Grasshopper!" timescale.

Now for the inevitable back-pedalling :

• Modelling like this is pretty uncertain. Sure, we've now got a mass estimate that is 19 solar masses (M_☉ hereafter) compared to previous mass estimates of 11~14 M_☉. That has a lot of consequence for the stars expected main sequence (MS) lifetime (16~9 Myr for the lower mass range, 4Myr for the higher mass range). The post-MS lifetimes also become much shorter as the star mass goes up, and the variability and the dust clouds and mass outflows visible in and around Betelgeuse rather suggest it's already in it's post-MS phase.
• It's almost unrelated to the "Great Dimming", which is most likely (IMHO) a previous dust emission, thinning and dispersing. That could easily happen on multiple century time scales, and could also affect the stars colour (as discussed by Neuhäuser et al, 2022, marked above). Which would weaken at least one major plank in this paper's estimate of Betelgeuise's mass. Since the invention of the telescope, we may never have seen Betelgeuse/s un-dimmed state.
• Dr Becky had doubts too, expressed on her "Night Sky News" vlog (timestamps 06:50 ~ 14:30) - but they're pretty similar to mine. I'd add to her "general principles" concerns that we also don't know the metallicity of the core of Betelgeuse terribly well, and thats … somewhere between likely to have an effect, and unlikely to have no effect. We think that the heat transfer from the core outwards is by radiation, not by convection, so the surface (photosphere) composition is decoupled from the core composition. How decoupled ... aye, there's the rub. (Smaller stars than the Sun, "M dwarfs", may be "fully convective", where convection stirs the core material into the main body of the star, but this takes time, and in the latter stages of evolution, things happen in the core on a matter of years, while mixing may be on much longer timescales.
• She was probably wrong about one thing though - the last supernova in the Milky Way wasn't "Kepler's Supernova" of 1604, but a previously unremarked star in Sagittarius, which went supernova between about 1890 and 1908 producing the radio feature G1.9+0.3. That was invisible from Earth behind dust clouds, but the supernova remenant (SNR) is obvious (and visibly growing) in radio wavelengths. Kepler's was the last naked-eye supernova in the Milky Way. It's very likely that humans will see Betelgeuse going supernova when it goes, because it's so close (450~650 ly, 150~200 pc) that it'll be naked-eye even during daylight hours (unless it happens when in conjunction with the Sun - approximately May to August, depending somewhat on the observer's latitude). Whether it happens before humans lose telescope technology is a more open question.
  Of course, all this attention on Betelgeuse deflects attention from other stars which have a good chance of being the next Milky Way supernova. There's Eta Carinae, trembling away like a Hollywood child actor's lower lip; a list of 31 candidates within 800 ly of Earth (OK, Deneb/ α Cygni is 802 ly, plus or minus error bars), and a lot of other runners and riders. (After writing this, a paper concerning recent strong dimming in the "hypergiant star RW Cephei" has added another, distant, name to the "runners and riders" list. See discussion below.
• It's almost inevitable in discussions like this that we have to re-stress that all the times mentioned in this topic are in Earth's reference frame, not Betelgeuse's reference frame. Yes, of course the star could have gone SN already, and the light (and neutrinos) from the event are on their way to us. But we won't know that until they get here. making the point moot. Astronomers understand this well enough that since before SN 1987A people have been plotting to observe "light echoes" from SNs (and ordinary novæ) bouncing off dust clouds behind or to one side of the (super)nova, including looking for the arival (at Earth) of light from flares and outbursts of the progenitor star before the "main event". (Eta Carinae has been a notable success in such searches, IIRC. I didn't make notes.)
  (Including this caveat won't mean that nobody re-flogs the bones of this particular flayed horse. Suffer, dead Dobbin, suffer!)

Routinely, when discussing "the big one", along with the dead horse flogging over reference frames (really guys, we get it. Why is it always guys who flog this flensed Equus?) there are questions along the lines of "are we all going to die?"

The answer is "almost certainly not". When we get a "big one", it'll be the 3rd or 4th in a millennium. One going off about every 250 years, that we see. Seriously, outside astronomers, almost nobody notices. Horses chowing grass might riase head from sward for a few seconds, then go back to grazing and worrying about internet trolls and temporal reference frames. Late night taxi drivers might ask "what's that light?". At the right time of the year, daytime people might repeat the question. And almost everyone will forget about it in a few days or weeks. Alart form astronomy nerds, who will be boring people to absolute death about it. Boredom by an astronomy nerd (or bludgoning of the same nerds) is likely to be the biggest death toll consequent on the next "big one".

Specifically, for Betelgeuse, there is one potential "everybody is dead" scenario which is very unlikely. Supernovae remain potential sources of Gamma Ray Bursts ("GRB", possibly also sourced by "compact body" (neutron stars and black holes) mergers, now visible to our gravity-wave telescopes), and one of those going off 600-odd ly away could be a potential bad hair day for a lot of people. Depending on how long it lasts, Homo sapiens mighte be depending on the crews of steel-hulled ships, oil rigs & submarines to bounce back from being hit by such. Which might be game over for the species, and certainly a rough time. But probably not either. Living organisms in the open might die. But all seeds below the soil's surface, nope. Ditto some organisms living in cave entrances facing in the right direction should get enough protection. It's very unlikely to be an "end of life" situation - a mass extinction scenario more likely (hint : 6 of the 7 biggest mass extinctions have obvious non-GRB causes). Even if it happens.

But for that - the Earth to be hit by the beamed energy from a GRB - to happen, we would need to be very closely aligned with the progenitor's rotation axis. Various imaging campaigns from the mid-1990s to the present see noticeable variation in Betelgeuse's brightness from epoch (date of observation) to epoch, which suggest that we're not on the stars rotation axis (the longer-established overall brightness variations argue similarly). A 1998 paper ("Spatially Resolved Hubble Space Telescope Spectra of the Chromosphere of alpha-Orionis". The Astronomical Journal. 116 (5): 2501–2512. Bibcode:1998AJ....116.2501U. doi:10.1086/300596. S2CID 117596395.) suggested that we're about 20° off the star's axis. Which is probably enough to protect us from the "relativistic beaming" of a full-on GRB, and reduce the radiation from a pulsar to about 1 second in 5 - which the atmosphere will reduce further. I just don't see Betelgeuse being much of a (realistic) GRB threat.

Besides, Betelgeuse is probably too small ; if you really want to worry about a GRB, worry about Eta Carinae - but that is around 10 times further away, which factor alone would reduce the radiation dose about 100-fold. And we're 30~45° from the axis of that system. So that's a big fat nothing-burger too.

That's enough Betel-juicing for now.

That was last night

This morning's IArXiv (summary of today's ArXiv postings, weighted by my responses to previous IArXiv listings; though I'm actually somewhat behind on drinking from this particular hosepipe) brings this comment paper : "Comment on the feasibility of carbon burning in Betelgeuse: a response to “The evolutionary stage of Betelgeuse inferred from its pulsation periods”, arXiv:2306.00287", which is various credentialled astronomers responding from Hungary and America. I've dropped the link to Dr Becky, since she's posted on this tool. What are they saying?

These people assert (to be evaluated) that Saio et al's interpretation of Betelgeuse's brightness variation as solely a consequence of pulsations in the diameter of the star is incorrect. "However, the angular diameter measurements of the star are in conflict with the stellar radius required by their models". So, are these objections justified?

I recall thinking, as I read Saio et al's estimate of the radius of Betelgeuse - derived from their pulsation model - as being "higher than normally suggested". But an inflated radius for red giant and red supergiant stars is, as the name suggests, rather normal, so I wasn't wildly upset about it.

From The Friendly Paper (FTFP), on the subject of the star's diameter, "However, measurements do not necessarily detect the visible-light photosphere of the star directly. They are affected by factors like limb darkening, spots, molecular layers and circumstellar dust." Which, yes, that's a large part of why I wasn't terribly upset by the difference between Saio et al's radius and previous estimates. These authors present a considerable compilation of "Visual", "V-band" (an astronomical wavelength-range filter) and "SMEI" ("Solar Mass Ejection Imager" ? Why would a solar telescope be pointed at Betelgeuse? From the first light photos, it can image the Milky Way, but … ) measurements that show Betelgeuse's 380~430 day variation very well, and less distinctly, the 2200 day period. These authors interpret the "Great Dimming" as a sporadic, out of phase event (such as release of a dusty cloud from the star's surface). Which might be an important point, if Saio et al's had relied on it. They mention it, say it was about a minimum of the "~400 day vairation", and then leave it aside as just another event in that cycle.

So basically the dispute here is whether the 380~430 signal is the star's radial pulsation, or if the 2200 day pulsation fits that rôle. The "Great Dimming" doesn't really come into it - it's a random event on top of the informative variation cycles.

The new authors then "work outwards" from the photosphere into interactions of the photosphere and the star's atmosphere. Which they say, prefectly correctly, are likely to have a significant effect on the star's external appearence - as the whole "Great Dimming", and observation of other stars would agree. However ...

A major point of Saio et al's work was to introduce into the discussion "Neuhäuser et al. (2022) …, marked above] interpretation of pre-telescopic records which reveal that this star exhibited significantly higher temperatures [up to] two millennia ago." (as I quoted in the first version of this article). And Molńar, Meridith and Leung don't look at that, they look only at essentially atmospheric effects, while Saio et al's work primarily addresses the internal heat engine that drives the photospheric effects which Molńar, Meridith and Leung are looking at.

Molńar, Meridith and Leung may have valid points about the "atmospheric" effects, but they don't really invalidate Saio et al's discussion of the internal power-source of the star. We're just going to have to wait to find out.

Now, does Dr Becky have owt to say?

See also the discussion of RW Cephei below. I can't get away from the topic.

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The World Is Not Enough - WINE - spacecraft ; hubris for those lacking in Classical scholarship.

https://arxiv.org/pdf/2306.03776.pdf

Boringly, the paper title is "Thermal Extraction of Volatiles from Lunar and Asteroid Regolith in Axisymmetric Crank-Nicholson Modeling", but I just love the idea of "the World Is Not Enough (WINE) spacecraft concept". Clearly someone has either not heard of the concept of hubris, and how various pantheons of gods have punished humans showing this characteristic. The designers will have to be tunr widdershins at the right moment, and perform their functional sacrifices with appropriate chanting burning of incense and prayer to the Gods of spaceflight.

What are they actually doing? Well, with Philip T. Metzger (on Twitter, @DrPhilTill on Twitter, while it's still alive) involved, you can guess its' something to do with the regolith on space bodies. In this specific case, they'ere looking at the (theoretical) efficiency of extracting volatiles (in general, water in particular) from regoliths on the Moon, asteroids and (potentially) Mars.

Previous work has shown (unsurprisingly) that in a vacuum, as you heat a sample of regolith the volatiles move away from the heat source, but the details depend on the vacuum, the temperatures, temperature gradients and many other details. A particular construction of mining machine could collect voatiles efficiently in one nevironment, and very inefficiently in another. So, there is a need to do multiple tests in various environments. Which is where the WINE (hubristic name expanded above) spacecraft comes in. In their words, WINE will be a small spacecraft, approximately 27U in CubeSat dimensions (3 by 3 by 3 cubes), with legs for walking short distances and a steam propulsion system for hopping multiple kilometers. […] WINE will drive a corer into the regolith to extract water and perform science and prospecting measurements on the regolith. The water will be extracted thermally by heating the material in the corer. Vapor will travel into a collection chamber where it is frozen onto a cold finger. After multiple coring operations have collected enough water, the tank will be heated to high pressure and vented through a nozzle to produce hopping thrust Which is a fairly ballsy set of optimisms.

They then follow with a lot of mathematical modelling, which really just serves to show that we don't have a large amount of experimental data on physical and chemical properties of regoliths, apart from a small amount of Apollo data density/ strength obtained by using core penetrometers (tube, hammer, measuring stick, notepaper) to collect soil samples. Some properties (thermal conductivity, density) were measured after several days transport and re-warming in the returning spacecraft, plus a sea landing. Yeah, I'm not going to put too much faith on those values without some "ground truthing" measurements. (These authors don't mention it, but if the "mole" of Mars Insight had worked, it would have provided at least one log of some of these parameters in Martian soil. possibly including sub-surface ice.)

The table of products form the LCROSS impact mission is interesting.

Volatiles in LCROSS Ejecta (from https://arxiv.org/pdf/2306.03776.pdf)

Compound	Symbol	Concentration (wt%)
Water	H20	5.50
Hydrogen sulfide	H2S	1.73
Sulfur dioxide	Si [sic, typo] SO2	0.61
Ammonia	NH3	0.32
Carbon dioxide	CO2	0.29
Ethylene	C2H4	0.27
Methanol	CH3OH	0.15
Methane	CH4	0.03
Hydroxyl	OH	0.0017
Carbon monoxide	CO	0.000003
Calcium	Ca	0.0000008
Hydrogen gas	H2	0.0000007
Mercury	Hg	0.0000006
Magnesium	Mg	0.0000002

I hadn't particularly paid attention to that previously. But having 1.73% of the ejecta mass as hydrogen sulphide is ... challenging. If you were to pump this mix into a chemical plant to make atmosphere, rocket fuel, whatever, you're going to want to either dump that stuff, or move the sulphur to a differentl, less hazardous, oxidation state. The simple process of oxidising it to sulphurous acid (H₂SO_{2 or 3}, which is relatively innocuous) would help, but would account for something like 1/3 of the potential oxygen output from electrolysing the water. Hmmm. That's a problem. Maybe just bring the sulphur up from oxidation state -1 to state 0 would be better. "Flowers of sulphur" is a damned sight less horrible a chemical to have near living quarters then H₂S. Someone is going to have to look at that.

There's a lot more work in this paper, modelling temperature changes in lunar soils through a day-night cycle, considering temperature profiles in the corer of the "WINE" spacecraft proposal. Lots of theory. Really, some of this needs ground-truth, and I'm sure this paper will be fairly heavily drawn-upon in arguments over which next missions to launch to the Moon (or various asteroids, or Mars) to evaluate their soils physical and chemical properties. There are a lot of free parameters in these models which need pinning down to something more closely constrained by reality.

Not a very "fun" paper, but probably quite important for actually building humanity into a space-dwelling civilisation, if not necessarily a Mars dwelling one. Who would want to live at the bottom of a hole? (Known Space reference.

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Stars with really long dimming events

Discovery of Gaia17bpp, a Giant Star with the Deepest and Longest Known Dimming Event

Do you remember where you were when Tabetha Boyajian said "Where's The FLux?" about star KIC 8462852 (KIC - Kepler Input Catalog)? That was a lot of a surprise (and still remains somewhat puzzling), but with the rapidly increasing completeness, cadence and sensitivity of astronomical survey programmes the number of - and extremes of magnitude and duration of - dimmings of stars recorded have beceom a commoner thing.

This is a new record-breaker. Until the next record-breaker. This star has spent about 6.5 years (2000-some days) in it's dimmed state - the start is somewhat uncertain between surveys which serendipitously covered this field in 2012 and 2013 - before which the star exhibited no obvious brightness changes. However with up to 11 or 12 year gaps in observation in the 1950s and 60s, other dimmings are plausible.

The interpretation - as for a number of other dimming events - is that the star's light has been dimmed by passing through an approximately neutrally-coloured disk of material orbiting a companion (or possibly independent, if this dimming is a one-off event). The modelled disc is at a small angle to our line of sight - if the disc had been inclined closer to face-on, the depth of dimming would have been less.

Similar explanations have been put forward for other "dimming" stars such as Epsilon Aurigae, though it's dimming recurs on a period of some 27 years, with each dimming lasting around 2 years.

We're going to see more of these. Lots more of these. Following the same arguments as justified the Kepler Observatory, around 1% of multiple star systems where one component has a significant absoebing disc will be detectable from Earth, given sufficient numbers of observations. Similar biases to close-in dust disk carrying companions will exist.

This model doesn't explain "Tabby's Star" KIC 8462852 - or at best, not very well. There are hints of periodicity in that one's dimmings, but there is a lot more stochastic noise.

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Astrophysics observatories as Seismographs

Status of the GINGER (Gyroscopes IN GEneral Relativity) project.

After the successes of gravity-wave telescopes (LIGO, to a lesser extent KANGA and Virgo ; and now the various *PTA "NANAOgrav discoveries.), people are naturally looking to turn it up to 11. s. GINGER (Gyroscopes IN GEneral Relativity) is a proposal to build a number of ring laser gyroscopes (a technology that has been used in surveying since almost the invention of the lasers) to "measure general relativity effects and Lorentz Violation in the gravity sector". Which I'm sure would be terribly exciting for physicists and astronomers everywhere. But the other stipulation, that the devices be "rigidly connected to the Earth", also means that these would both be subject to non-trivial levels of seismic noise, and would also serve as a remarkably broadband seismograph. The seismic noise they've got a technique for, as deployed by LIGO Hanford and LIGO Livingstone, by having two (or more) more-or-less identical machines at considerable separation, and having some degree of appropriate coincidence detection and rejection to differentiate between GW signals and seismic signals.

That is going to be more challenging with two sensors at one location.

(The proximal part of "GINGER", time wise, is about building two "technology demonstrators" in the existing deep underground lab at Grand Sasso, which is currently used for low-radiation-background experiments, neutrino detection, dark matter telescopes, that sort of thing.) They'd have to interface with more conventional seismic networks to reject the "understood" noise sources, which would leave the not-understood signals in the noise. Or for that matter, in the not-previously-"understood" signal. But I'm sure that's do-able, before building a second site. Or fully interfacing with one of the various other high-sensitivity ring gyro systems under development.

That's viewing the seismic noise as noise. But of course, it's also going to be an exquisitely sensitive seismograph. If they're looking at sensitivities in the order of 1 part in 10⁹ to 10¹¹ that would imply a bandwidth down to around millisecond or microsecond signals (since they're looking towards astronomical sources from an Earht that rotates in approximately 10⁵ s. That's a pretty good step up for seismography. And the physicists pay for it! What's not to like?

The project already has, they report (references in original paper), collapborations with high-precision observatories in Germany (G9 at Wettzell and ROMY in Bavaria), New Zealand (U.o.Canturbury) and China (HUST, Wuhan)). That Wuhan connection is going to bring the anti-vaxx freaks out of the woodwork, though I'd be moderately amused to see how they get from Length-of-Day and Earthquake measurements to Bill Gates' 5G mind control chips in the COVID vaccines. After all, it can't be coincidence. Those pre-existing collaborations are proof positive of nefarious and long-standing plans.

I see, checking those co-project's references, that several of the paper's titles include reference to siesmic and seismological results. Evidently they too have seen this ... interdisciplinary link. So they're probably touching the seismology community for some contributions of "folding" already.

As a footnote, this is a contender for the DOOFAAS project. If you like it, mail that project's instigator. It is not known if ACRONYM software was used to construct this ... "name". Or if it is natural talent on someone's behalf.

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Another Great Dimming - not Betelgeuse

The Great Dimming of the hypergiant star RW Cephei

It seems as if this month's recurring theme is the dimming of Beteleuse, but many other intrinsically bright stars also have irregular dimmings, as well as more regular periodicities in brightness. RW Cephei is another such. Although it is a lot brighter intrinsically than Betelgeuse, it's not so well known because it's further away. We can't actually tell how far away to within a factor of 2 - estimates on Wiki give it at 3,416 or 6,666 pc (11,100 - 21700 ly) - an eighth to a quarter of the way around the Galaxy. It's not clear why the distance is uncertain, but the presence of an extended envelope of emissions around the star probably doesn't help. That's 10 to 20 times the distance to Betelgeuse, so it's not a bright star in our sky.

Cepheus is a circumpolar constellation from the UK, but it's not terribly well known because it's not got many bright stars. As seen on the sky, it is to the west (anticlockwise, widdershins, centred on Polaris) from the bright "W" asterism of Cassiopeia. RW Cephei is in the Cassiopeia corner of the constellation, though actually closer to the border with the dim constellation of Lacerta. It's well below naked-eye visibility during the current dimming, but at it's brightest should just be visible under excellent conditions.

Despite being a lot further away from us than Betelgeuse (which has been subject to interferometric disc-size measurement since the 1920s, and more recent actual disc imaging), RW Cephei is such a large star thet it too has a disc capable of being imaged. This paper reports on the imaging results. THe observations were carried out with the CHARA telescope array, comprised of six 1m telescopes with delay lines so that act as an interferometer with a resolving power of 200 µas. These results couples with the distance estimates given above indicate a stellar radius of 900 to 1760  R_☉, making it one of the largest stars measured, to date.

The report also includes AAVSO data for RW Cephei's visual brightness (with Betelgeuse for comparison) as figure 1 :

Caption :

If you want, you can get updated data from here. At the report's writing, the dimming event had lasted about 1100 days (compared to about 200 days for Betelgeuse's recent dimming and 2000+ days for Gaia17bpp described above). At points in the deepest part of the dimming, the magnitude was being reported as 8 (visual), compared to the normal range of brightness of 6.0 to 7.6 . The most recent (late July 2023) AAVSO data has the brightness back to about M 7.0, well within the normal range of variation.

But that's not the exciting thing in this report. What this has, which most reports like this don't have, is that with the telescopes set up for interferometry, the observers could map variations in the brightness of the star's surface and reconstruct the image of the star's surface. Which has been done before (with Betelgeuse, for example). But this is on a star an eighth to a quarter of the way across the galaxy, and a considerably more luminous star too. RW Cephei is about 300,000 times the Sun's luminosity (300,000 L_☉) while Betelgeuse is less than half that (90000 - 105000 L_☉.

The first level of reconstruction produces these images (fig 5 upper) :

But those images combine both changes in colour and intensity, which include the effects of limb darkening. If you account for that effect, you get a better impression of what is happening to the star itself. (fig 5 lower, and caption)

The colour and/ or shape variations of these images probably reflect variations in the temperature of the star's surface, which for a large star is thought to be dominated by convection cells bringing heat from the interior to the surface. But the largest stars have a competing process of mass loss with both material jetting off the surface into space (which implies cooling, with spectroscopic consequences, which can be seen) and also the release of dust to form obscuring clouds between us and the staR - a process thought to be happening with Betelgeuse.

Section 3 of the paper reports near-infrared spectroscopy taken during the dimming. Through most of the spectrum the intensity is lower than in archived (normal brightness) IR spectra, but the change is greater at shorter wavelengths. With some well established physics this can be turned into mean surface temperatures

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And now the end-of-month tidy-up. Only 3 overhangs.

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Red Supergiant Candidates for Multimessenger Monitoring of the Next Galactic Supernova

https://arxiv.org/pdf/2307.08785.pdf

Science wise, this is just a catalogue of these candidates. But it’s also a public bet. 677 public bets. The justification is to shorten the list of candidates for pointing “light buckets” at, in the event of an early detection of a likely supernova by neutrino telescopy. If (“if”) one or several of the operating neutrino telescopes (French ANTARES, Antarctican ICECUBE, Russian BDUNT, Japan’s SuperKamiokaNDE …) detect a burst of neutrinos incoming, and can get a directional fix (some are more directional than others) then we may have an approximate detection.

The neutrino burst from a star's core collapse (or potentially, a gravitational wave signal) should escape from the core of a star in seconds (about 5 seconds for the Sun) to the surface where we can see it, while the explosion shock wave can take hours to days to emerge (“shock breakout”). Thus, a prompt observing campaign could capture brightness, spectroscopic or even compositional data on the star as close as possible before the actual supernova. Hence, a catalogue of “usual suspects” could help with prioritising candidates. It’s a numbers game, but with a reasonable chance of prompt payoff. The 1987A supernova in the Large Magellanic Cloud was accompanied by a burst of 20 (or maybe 25 - 1 of the 4 detector instruments involved is discordant) neutrinos and antineutrinos 2 to 3 hours before the first optical detection of the star's brightening. That's a very useful amount of warning.

Probably major observatories are already incorporating this into their “Target Of Opportunity” (TOO) decision process. To a significant degree, time and date are going to affect each observatory’s listing, day by day and hour by hour, but also which instruments are deployed, the slewing time from [current target] to [TOO] to [next target] … it’s not something the night shift operators would want to have to do “on the fly” without prior planning.

The criteria used for inclusion in the catalogue are luminosity (absolute, obviously, which requires a reasonably good distance from the Gaia stellar catalogue), temperature (requiring at least multiple filter measurements, if not full-blown spectroscopy, so not all potential targets have this data available, to this date ; that'll change), and chemical contamination (also requiring spectroscopy).

Obviously there’s a lot more detail in the selection process. But the core idea is there.

The catalogue is online on GitHub , but is also already incorporated into VizieR, a standard astronomical database collection. (I need to improve my VizieR-fu! Ditto the “Jupyter notebook” mentioned on GitHub, which I’ve heard of but never needed to use.)

I’d already got a catalogue of 112 RSGs and B binaries in my astronomy workbook, so I’ve added this lot. Plus a list of 31 potential progenitors from https://arxiv.org/pdf/2004.02045.pdf - which list is of suspect stars within a kiloparsec (3200 ly, approx) whereas this more spectroscopic list has nothing closer than about 250 pc (it gives parallaxes in mas, not pc). The lists use different sets of names, so are hard to compare directly, but at least three stars (HD 17958 (HR 861 in Cassiopeia, Gaia DR3 ID 467907038749283000, DR2 ID 467907038747132000, 2MASS ID J02562466+6419563), HD 80108 (HR 3692 in Vela, DR3 ID 5423960064637140000, DR2 ID 5423960064637140000, 2MASS ID J09162303-4415564) and HD 205349 (HR 8248 in Cygnus, DR3 ID 1971358279140130000, DR2 ID 1971358279140130000, 2MASS ID J21331788+4551142 ) appear on both lists.

Ye gods, and by gods I mean Cthulhu and the FSM , I'd forgotten how bad star names were. It was bad enough with AB Doradus and ZZ UMajor a decade ago, but these Gaia ones are a factor of several worse. If only they were comprehensive catalogues. But that's not really feasible this side of 102,023 CE. Sorry, 1,102,023 CE, because we'd need to geet to the other end of the galaxy. and get the signal back. That's assuming an average human expansion rate of 0.1C, and a speciation rate of zero - both of which are rather implausible.

If you can find any more "duplicates", you're welcome to. And you deserve a chocolate biscuit.

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Exponential distance relation (aka Titius-Bode "Law") in extra solar planetary systems

https://arxiv.org/abs/2307.06070

Titus and Bode’s “Law” was an exercise in applied numerology which became popular once the geometry of the Solar system became calculable, using Newton’s dynamics, plus measurements of the Astronomical Unit (AU) by observation of parallaxes, and specifically transits of Venus across the Sun’s disc. Per Wiki, the first statement was in 1715, with variations and various authors (including Titus and Bode, and others) until 1772. When Uranus was discovered in 1781, which fitted reasonably closely to the “Law”, it became more popular. And when Ceres (now classified as a dwarf planet) was discovered in 1801, further numerology ensued. And again, with the discovery of Neptune, in “not-quite” the right place, more flogging of the never-alive horse happened. Pluto, also not being in quite the right place, further encouraged the numerologists. With 3 (or 4) parameters (for different ways of expressing the idea) and 7, 8, or 9 data points (for planets, dwarf or not), anyone could join in the fun of trying to make a better-fitting model. However, no “universal” solution of free parameters has been found – every system has different parameters.

If the Solar system had formed by natural processes (potentially a question in the 1700s, not so these-centuries) then it’s appealing to expect that there should be some relationship between the orbits of the planets. Unfortunately, “appealing to shaved apes on a mud-ball” isn’t a particularly compelling argument to planets in other stellar systems or scientists anywhere. It would be harsh to call it “not even wrong”, but it’s not very well founded in physical reality for a number of reasons :

• as generally presented, the Titus-Bode “Law” looks for relation in the semi-major axes of bodies orbits ; but basic Newtonian gravitation (Einsteinian too, not that it matters) shows that the biggest forces between planets would occur when the outer planet is at perihelion (nearest point in the orbit to the Sun) and the inner planet at aphelion (furthest point from the Sun), when they’re in the appropriate phase relationship. And on a significant time scale (I’m a geologist – the mega-year is a convenient unit) phase relationships do change.
• orbits evolve with time. They evolve significantly. Today’s measurements of orbital parameters are good for predicting what they will be next year, and not bad for predicting a million years hence. But a billion years … nope, you’ve got no real choice but to calculate it numerically because those 10th decimal places really do add up over time. If you do a lot of calculation of models there is, for example, about a 1% chance that Earth will be hit by Mercury before the Sun goes red giant. That’s a consequence of Mercury – the second least circular planetary orbit, if you include Pluto as a planet – occasionally approaching Venus relatively closely, which increases Mercury’s eccentricity leading to closer approaches … and 1% of the time, Mercury gets ejected from the Solar system, but finds Earth in the right place at the wrong time. (Don’t worry, the Earth’s oceans boil and the Sun goes red giant with pretty much 100% probability. Even if another star hits the Sun (less than a billion-to one chance, even when the Andromeda galaxy hits the Milky Way), that’s only going to bring the red giant date forward.)
• there seems to be quite a lot of randomness in the development of planets. If our best model of planetary formation is right, little things (dust grains, sand grains, dirt balls, asteroids, big asteroids) meet to form bigger things until they run out of bigger things crossing their orbits. At all stages similarly-sized bodies are colliding and merging– which is a sensitively random process. When people tried modelling the “Moon-forming impact” in the late 1980s (when supercomputer power became affordable), they discovered that it was exquisitely sensitive to the impact factor (distance between proto-Earth centre and projected path of the impactor), and to the rotation rate of both bodies. I’ve got a compendium of evidences for “late giant impacts” in the Solar system, and the only planet without good reasons for believing there to have been a “late giant impact” is Saturn – the one with the recent debris rings and the “Death Star Moon” Mimas
  
  ). Yeah, not a lot of evidence for giant impacts and hierarchical growth around Saturn.
• Would you really expect a Titus-Bode like "Law" in the satellites of a planet within a stellar system? That’s quite unintuitive to me – surely the gravitational influences of the other planets would be have an effect, particularly on the outermost satellites where the statistically greatest influence on a “Law” would happen, per satellite. You could view the satellites of a planet in a multi-planet system as being somewhat similar to the planets orbiting one star in a (widely-separated) multiple-star system.

So, yeah, it’s maybe not so obvious that there should be a Titus-Bode-like "Law" for planetary systems. Certainly not to me.

FTFA, the authors find that an exponential (“Titus-Bode-like”) model fits the 32 reasonably-sized (i.e. 5 or more planets) planetary systems known to date. They use “R²” and “Median” comparison statistics – (I know “R²”- Pearson’s correlation coefficient. Their “Median” test test though is the https://en.m.wikipedia.org/wiki/Average_absolute_deviation which is a moderately well-known description of clustering in a data set around it’s central point. Here they’re using the mean as a measure of central tendency: ) $$\mathit{Mean}\mathit{Average}\mathit{Error}(\mathit{MAE})=\frac{1}{N}\sum _i\left|y_i-\widehat{y_i}\right|$$ (y-hat being the sample mean).

Historically, the Titus-Bode “Law” expression started from Earth’s orbit, and went both in- and out- wards. These authors (like many others) simplify matters by working from the smallest known orbit and just working outwards. Which makes for a simpler expression :

$$r(n)={\mathit{ae}}^{2\lambda n}\phantom{n=n}n=\mathrm{1,2,3}\dots$$

The authors are careful to exclude multi-star systems from their consideration. That suggests (to me) that the effects of the lighter star being closer to the inner planets some times - but not others - would be an issue.

By generating naïve artificial planetary systems and analysing them similarly to the actual star systems they get average regression values of 0.905 while for the Kepler poly-planet set it’s 0.966 – appreciably better. It’s unsettling that they find the (generalised) Titus-Bode "Law" to be a good descriptor of planetary systems, when I’m so disparaging of it. But they agree with me that the lack of a physical basis is problematical.

An interesting sideline is that by introducing a physically realistic constraint on placing of their “pseudo planets” in their pseudo-systems (separating planets by several Hill radii https://en.m.wikipedia.org/wiki/Hill_sphere ), their pseudo-systems approach the statistics for Titus-Bode models. That’s … suggestive. But far from convincing.

The authors spend some pages discussing the use of the Titus-Bode "Law" (originally, and in more recent formulations) to predict the positions (well, semi-major axes ; equivalently periods) of as-yet undiscovered planets. As always, the example of the discovery of Ceres is touted, and indeed, the search that yielded Ceres does actually fit the original Titus-Bode "Law". The surprising thing is that the search didn’t find Neptune, with over three times the angular diameter (though something like 1/10th of the overall brightness, so maybe not that surprising). However, Ceres itself, and the whole asteroid belt adds up to really, really little. People get this wrong. They think the asteroid belt is much more significant than it really is. By mass it is about 0.004 that of Mars (proportionally less than half the size of Earth's Moon), and 0.0004 (count the zeros! I did.) of the mass of Earth. The lack of mass in the asteroid belt has long been a problem for people trying to work out a reasonable scheme for building the Solar system from a circumstellar disc (such as we see around protostars and young stars today). Considering that, really we should do calculations about the Titus-Bode “Law” excluding both Ceres and Pluto, since they’re so small and almost massless that they can’t greatly influence anything of significant size at significant range.

While I’m worrying about Ceres’ mass, the next section of the paper comes along … suggesting the Titus-Bode “Law” may in some way be related to the age of a planetary system, as if it had been “running in” like a coarsely-machined engine. Problematically for this thesis, what you need for shuffling the components of a planetary system around is, bluntly, mass. But by including Ceres in their considerations as a “planet”, they’re also saying that, in their opinion, mass is unimportant. Fortunately, their correlation is no correlation. “Correlation is not causality” may be a mantra of statistics lecturers (even if the students tend to forget it), but “No correlation means no causality” is a considerably more firmly based claim. The authors dug this pit for themselves, then chose to not climb into it. Well done.

But then the next section they choose to throw themselves back into this pit. After a not-unreasonable discussion of the mutual influence of neighbouring planets on each other’s periods and spacing (see above comments about mass), they go on to say It is in fact well-known that “small” objects, like comets, small asteroids, debris, etc. do not follow, singularly, any particular pattern in the size of their orbits, and can be found at any distance (allowed by classical mechanics) from the central body. and then they go on to consider Ceres to be significant in the dynamics of the Solar system. Dodging a bullet is a skill, but getting hit by it after dodging it is a really difficult skill.

There may be something to the “Harmonic Resonances (HR) method”. But not by using this argument. Not if they’re considering Ceres to be throwing Mars around. Their subsequent point is that the "HR method" generally uses distinct “small number” ratios between neighbouring planetary neighbours, so the system effectively has approximately two free parameters per planet – which would practically guarantee a fairly good fit. That's well-founded. So, why pay much attention to the "method"?

Apparently the journal Icarus refuses to accept papers purporting to improve the Titus-Bode “Law”. I can understand why. Archaeology journals probably don’t accept many papers on von Daniken blurb or, latterly, Hancockian ink-waste. There may be something behind the (“a”, generalised) Titus-Bode “Law”, but it still has no theoretical basis, and it is (IMO) very problematic that real planetary systems (at least, the Solar system, and several young extra-Solar systems which have large excesses of dust) seem to have had significant but essentially stochastic (random) events. You might end up with a Titus-Bode-like "Law" from some filtering or damping of an initially random system, but that is a connection that hasn’t yet, to my knowledge, been made. And this paper doesn’t do it either. It’s probably worthwhile trying it, but this sort of numerology isn’t likely to do it. Numerical modelling of evolving systems in silicio is more likely (IMHO) to get somewhere in the right direction.

One thing that worries me is how all this depends on counting planets (gravitationally significant bodies) out from the star. If you’ve got a “hot Jupiter” in a 3-day orbit so close to the star that it's tidally locked, there probably isn’t room for a stable inner un-detected planet. But in the Solar system the innermost planet is also the smallest, and therefore the hardest to detect (by most methods). So surely, when looking at “adding planets” to an observationally based model, the case of an undiscovered small innermost planet is one that should be considered before messing around adding planets further out.

And no, Ceres still is not a gravitationally significant planet. Pluto is over twice the diameter and 13-odd times the mass, and I’m not screaming for it’s re-inclusion as a planet. (For the record, I’d have gone for a gravitational rounding + orbiting the star(s) definition rather than the IAU's “clearing the orbit” method. But I’m a geologist not an astronomer. And I’m definitely not going to get into that fight.)

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And finally I'm caught up!

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Weird deep-sea plesiosaur

https://twitter.com/Prehistorica_CM/status/1416089188563406857?s=09

High lung capacity - but does that help with compression?

Skull features mentioned.

I read the paper, but it starts a long, deep dive into the literature to get to why they think it's specifically deep-diving adaptations. Needs considerably more work.

I roughtly translated a Russian paper about this.

Iceland Bathymetry

I've always been interested in bathymetry - well, at least since needing to produce meaningful "location map" inserts for well logs at work. I've used things ranging from a geology server on Cornell.edu 's system to (since I left work) a tool called GeoMappApp (GeoMapApp (www.geomapapp.org) / CC BY).

This morning someone posted on Twitter a partial picture of Heezen & Tharpe's 1968 seabed topography map (to be more precise, Heinrich Berann's 1977 painting of Heezen & Tharpe's 1968 cross-ocean profiles), which prompted a question by another user about the "ring around Iceland". Which is why I'm interrogating the GIS.

Firstly, we need a bit motre detail on the bathymetry. Note that we're over 50 years later than the data Heezen and THarpe were working with, so we've a lot more data than they had. But it has to be said, Iceland has always valued - and therefore mapped - it's nearshore fishing grounds. So their data in the mid-1960s was probably pretty good for the first 300-odd km.

Bathymetry map of North Atlantic, centred on Iceland. White line is the associated N-S depth profile.

The white line shows the position of this profile. Note that sealevel is 3/4 up the vertical axis. Also note the vertical exaggeration is 125× ; distances are south from the origin, near Scoresby Sund on the East coast of Greenland.

You can see a definite "surface" around Iceland close to shore - between km marks 600 and 700 - which is very typical for around islands. (Damn, I forgot to put a scale on the bathymetry plot.) It's where wave action breaks up rock and moves boulders around until the sediment "falls off the edge" into the abyssal deeps. (This also appears on the next profile, alonf the Scottish margin, which is mainly composed of multi-billion-year old high-grade metamorphic rocks - much more consolidated than fresh lavas which erupted into seawater.)

From 700 to 1200 km from the start point, you can see that the seabed level (above some particular level in the mantle) declines failry steadily. Not uniformly, it looks more like what the mathemeticians call an "asymptotic" curve - always approaching a certain lline, but never quite getting there. If you, dear reader, want to play with the numbers yourself, I have the data file along this track line under the name "IS-profile-NS.txt". Some header lines :

GMRT Grid Version 4.11
Longitude Latitude Distance (km) Elevation (m)
-20.88 69.50 0.0 -378.21484
-20.88 69.48 2.9305084 -374.4984
-20.88 69.45 5.864622 -379.54816

(The original file is tab-separated, not space-separated, but that shouldn't cause any significant problems.

The general opinion of this profile is that the predictable decrease in the seabed level is the result of the deper parts of the crust slowly cooling as they move away from the heat inputs at the mid-ocean ridge. That's very compliant with the rest of physics - density changes with temperature, Archimedes and his post-bath streak through the streets of Syracuse, all that jazz.

But I have to admit that for the specific case of Iceland, I had to select my profile fairly carefully, because to the NW and SE are complicating structures - the Fareoes (DK : "Far Islands") ridge and the Iceland-Greenland ridge. These are the surface traces of the movement of the comtinental shelves and newly-created oceanic crust over the margins of the Icelandic hotspot, which has resulted in the accumulation of considerable thicknesses of lavas on the surface (I've drilled oil wells on the UK side of this region ; basalt and eroded lava beds and intrusions are common for the top several kilometres.) and sub-surface heating from some flow away from the hotspot. The textbook image of a hotspot is that they're circularly symmetrical, but as seismic data improves it is becoming increasingly clear that they're not simple, or circularly symmetrical. Or even, verticallt straight. By coincidence I was reading a paper on the topic just a few days ago ("Imaging deep-mantle plumbing beneath La Réunion and Comores hot spots: Vertical plume conduits and horizontal ponding zones", Dongmo Wamba et al., Sci. Adv. 9, eade3723 (2023) 25 January 2023) which gives a much more geological "feeling", complex structure. That this SW Indian Ocean example shows plumbing structures in the mantle of several thousand km size N-S, E-W and Up-Down feels - to me - more realistic than simple cartoons of circular structures. In the volume of the Earth, nothing is the "spherical cow in a vacuum" that physicists (stereotypically) start with ; everything has a history, which affects it's present and future. Complications of the "Icelandic hotspot" stretch at least as far as the island of Lundy in the Bristol Channel, the line of "Tertiary Volcanic Districts" (as the regional geological memoirs are titled) from Ulster to Arran to Mull to Skye to the Forties oilfield (intimately associated with the whole Central North Sea oil province), a slew of seamounts and dead volcanoes between Orkeny and the Faroes, the Faroes themselves, and I literlally do not know what is further up the Norwegian Atlantic coast. Really quite comparable with that paper's Comoros-Mayotte-Reunion-Marion-Crozet-Kerguelen sub-crustal plumbing.

Taking a profile perpendicularly across the Ridge direction, from the mountain rim of Greenland, through Iceland, over the Faroes to the Shetland Islands, shows a more complicated set of elements :

Within Iceland, dips to almost sealevel speak to marine and ice erosion to that (approximate) base level (probably with some filling by sediments, also accumulating to approximately sealevel), then continuing to the East (increasing distance from the start point), between about 700km and 1300km the seabed sinks along a similar shaped profile to the N-S profile, though at a devreased rate. Then is a interval going above sealevel - the Faroes - which appear to have either a lot of build-up, or some thermal support from below. Then there is a trough (not a subduction trench, but probably fault-controlled) which reaches down to approximately meet the previous "thermal sinking" curve. Then there is the Scottish continental slope, and the wave-cut surrounds of the continentals shelf around a relatively small island group. (Text file of plot data is IS-profile-NWSE.txt)

This final set of images is across the Reykjanes ridge, a few hundred km SW of Iceland, and somewhat away from the complications of the hotspot.

Here the decrease in seabed level away from the ridge is much more clearly symmetrical about the ridge axis. The axis is still a thousand metre tall range above the "abyssal plain" - compare it with the Greenland mountains above sealevel.

The data file for this plot is "/home/aidank/winxferdir/Portable/geomapapp/GMA outputs/IS-ReykjanesRidge-Profile-NWSE.txt"

I've uploaded all the images and data files to a folder on "Box", but I'm not sure how that is visible from the outside world. https://app.box.com/s/skg097kuinerqy52b89xvuain2d7qweb Suck it and see!

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There's an annoyance - the Wikipedia page for Marie Tharpe cites her as having "discovered the Mid-Atlantic Ridge", while the page for the Mid-Atlantic Ridge correctly cites the discovery to the Challenger oceanographic survey voyage in 1872 - some decades before Tharpe, and probably her parents, were born. I'm fed up with correcting Wiki and being reverted, so do what you want with the correction. I'm not disputing Tharpe's contribution, but the first awareness of a tall mid-Atlantic underwater topography feature came from laying trans-Atlantic telegraph cables in the 1860s, and has been incredibly well reported. Amongst people who know what physics is. Well, ::SHRUG:: if someone more dedicated to Wikipedia wants to fix it, feel free.

2023-05 May Science Readings

2023 May Science Readings

May the 11th, and I have only just started. This isn't going to be a productive month.
A bit of progress by thw 18th.

Articles studied this May - some of which might go to Slashdot.

WTF is a Magrathea planet?

Thorne-Żytkow objects

Sporadic rotation in tightly-packed planetary systems

Some Tweets.

Replacing Areceibo?

The Winchcombe Meteorite.

Mantle structure below HotSpots

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I've got my keyboard better set up for accenting etc, and that's worth remembering. But it's not really a thing for this page. And I need to work on the redshift calculator (online version). [I still can't see what I was concerned about.]

Well, now I've got a problem. Why are my changes to my CSS not updating?

P …

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WTF is a "Magrathea Planet"?

ArXiv : Statistics of Magrathea exoplanets beyond the Main Sequence

Do people these days need to reference that Magrathea is a fictional planet in Douglas Adams' "Hitchhiker's Guide To The Galaxy"? Hopefully not, but if so, follow the link.

From the radio series/ books/ TV series/ films, the planet is sufficiently Earth-like for an unmodified tea-drinking slightly furry English-person to walk across the surface, picking his way between the lumps of confused sperm whale, armoured in a slightly battered dressing gown. So, essentially, Earth-like.

But what is a "Magrathea planet", according to these astronomers? Well, I'm not sure exactly how they got from the book description to a "system[s] in which the planet survived the [white dwarf] formation of the stars in the binary." In particular they're looking at planets around double-white dwarf systems, of which "No exoplanet has been found orbiting double white dwarf (DWD) binaries yet." That terminal "yet" suggests they have some reason to believe that there will be an announcement, some time "soon". Watch, as they say, this space.

There is a hint in the books etc that the Magrathea "civilisation" (Adams' own expressed doubt) is quite old in human - and "galactic" - terms. Which goes with a relatively old stellar system … there are a lot of caveats to put in there, but it's fiction, so not worth getting too bothered about. These scientists seem to have priority on re-using the term in an astronomical context, and I guess we pretty much have to accept it. They're a moderately interesting type of planet, but ultimately not going to be that common, compared to main sequence star's planets.

The "gas giant" aspect of the definition is in contradiction to Adams' earth-like scenario, but does mean the class is of relatively detectable planets. The main difficulty is likely to be in finding "DWD" systems, because by definition, they're going to be dim. The closest WD to Earth is the Sirius (absolute magnitude +1.43) and it's companion WD, ("Sirius B" sometimes called the "Pup", absolute magnitude +11.83, on a 50-year orbit about the primary) which is about 10.4 magnitudes (a factor of 14400-fold) fainter. As a "DWD" system, we certainly wouldn't have spotted tis until the 1700s, if not 1800s, while as it exists today, it's the brightest star i nthe sky after the Sun.

As a class of planets, it's a logical class, and this is a name for it. But it's not ever going to be a particularly common class, compared to those around G₀- or M- stars.

There are other science uses of "Magrathea" in software ("Magrathea-Pathfinder: A 3D adaptive-mesh code for geodesic ray tracing in N-body simulations") and experiment ("Magrathea: Dust growth experiment in micro-gravity conditions"). Both are in the field of "building planets", which was the business area of Adams' Magratheans. Which is all good fun.

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Observational predictions for Thorne–Żytkow objects

https://arxiv.org/pdf/2305.07337.pdf

Well, I had to search my note to remind me how to type the (capital-Z-upside-down-caret) character. (It's Super-.,z on my machine.) But that's not the big point. What the fsck is a Thorne-Żytkow object? Thorne–Żytkow objects (TŻO) are potential end products of the merger of a neutron star with a non-degenerate star. Ohh, so, the popular trope every time there is some science news about a black hole or neutron star, "What would happen if this entered the Solar system? is right up this street.

There has obviously been theoretical work in the past on this, because the paper doesn't start with the NS entering a photosphere. They seem to have their NS already at the core of the "non-degenerate" star ("the Sun" for the Internet wail). Previous work (1975 to 1991) suggests that Depending on the mass of the combined star, it can be supported either via nuclear burning on/or near the surface of the NS and by accretion onto the NS. Which is rather what you'd expect, if you think about it for a few seconds. The situation isn't that far from what happens to a NS in a binary system, as it accretes material from the non-compact star, except (this is important) there is enough material compressing the burning area to not go down the SNIA route of a thermonuclear "standard" candle, but it burns in a quasi-steady state. The normal scenario of a SNIa is for a white dwarf (WD) to be doing the accreting, but you could try doing it with a NS too. The difference in surface area between a WD (approximately Earth-size) and a NS (typically 3km in radius) is going to change things a lot though.

TZOs may be news to me (though I've got to say, I had wondered about the question myself, but never researched it), but they've been a subject of work since the mid-70s, have a Wiki page, and I (probably you too, dear reader, should you exist) would be best advised to read that first. A TŻO has an estimated lifespan of 10^5–10^6 years. Given this lifespan, it is possible that between 20 and 200 Thorne-Żytkow objects currently exist in the Milky Way. answers several very obvious questions. What happens then? It has been theorized that mass loss will eventually end the TŻO stage, with the remaining envelope converted to a disk, resulting in the formation of a neutron star with a massive accretion disk. Very well and good.

A candidate TŻO was proposed in 2014, and they've been linked to other classes of odd stars (Wolf-Rayet stars, RCrB variables ... ), but that attribution has been challenged with an alternative candidate proposed. There are now a half-dozen eight candidates, some of which are well-known RCrB variables.

From Wiki, they're also associated (potentially) with "strange" stars (in the quantum chromodynamics sense), and hence tetraquarks and pentaquarks, all of which have appeared in my reading lists over the last few years.

So, what does this paper add, now that I've dragged myself up to speed on the base phenomenon?
By using different computer models for the nuclear chemistry that would go on on the stellar core to NS boundary, this paper makes different predictions for the nuclear make up (and so, eventually, spectroscopy) of the star. And ... it's over to the observational astronomers.

I've dropped the data into the TŻO wiki page "talk" section. I've had too many snotty responses from Wikipeople to waste effort putting it in myself.

Dramatis Personae

An obvious question is, who are Żytkow and Thorne? I don't recognise Żytkow's name, but is the "Thorne" "Kip" Thorne of various GR and gravity text books? And indeed, it seems to be him. The other author, Anna Żytkow, is a new name to me. See her Wiki page.

Edit : connected to this article from Jan 2024.

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Day ‘N’ Nite: Habitability of Tidally Locked Planets with Sporadic Rotation

https://arxiv.org/pdf/2303.14546.pdf

Quite a short one here. In a "compact" planetary system - lots of planets in close orbits tight arouind a (typically) small star, it has generally been thought that the planets woulf be tidally locked - rotating about their own axis in the same time (and sense) as they orbit the star - so that one part of the ground points permanently to the star while it's antipode points permanently to outer space. A number of SF authors have used such planets as interesting locations to set their stories, including (just two I remember) "Proxima" and "Ultima" by Stephen Baxter. In a different setting, Larry Niven looks at the "star unmoving in the sky" in different artificial habitats on "Ringworld" (1970) and on the "Bowl of Heaven" (2012). Is there something about SF authors that makes them interested in "abnormal daylight hours"? Chronic insomnia and disturbed sleep patterns, maybe?

The work here is a mathematical study of the influnce of one planet upon another in such systems. The authors find a significant number of planets can interact to torque each other between locked rotation (do I need to point out that in tidally-locked couples, both bodies are actually rotating, just at the same rate?), and rotating at various rates. The transition between rotating (with respect to the star) and non-rotating can be chaotic, with periods of chaotic rotation occupying around ⅕ of the time between periods of tidally-locked rotation - which can put a reference location near the "sub-solar point", or the "anti-solar point", fairly rapidly.

Which would make for an interestingly different place to live.

Whether it's an interesting place for an SF author to drop some small furry Centaurian creatures into (with a criminally negligent pre-colonisation survey) ... well that's a question. The "chaotic rotation" doesn't mean that one day the "Sun" rises in the middle of the sky as normal, then it starts to move to the east, does that for a couple of days, then reverses to travel to the west. However the small furry Centaurians define "sunrise", "east" and "west". No, the chaos of rotation state swaps for periods of thousands of years (orbits), not on a day by day basis. With orbital periods of a few weeks, that's maybe not such a dramtic problem. And the Good Doctor himself managed at least one story with a once-in-10,000-year event ( Nightfall)

Is there much more to the science? FTFAbstract, A recent study shows the dynamical conditions present in the TRAPPIST-1 system make rotation and large librations of the substellar point possible for these planets, which are usually assumed to be tidally locked. - which is basically what I put above. Also in TFAbstract : Our findings show that tidally locked planets with sporadic rotation are able to be in both long-term persistent states and chaotic states: where rapid transitions between behaviors are present. Quasi-stable spin regimes, where the planet exhibits one spin behavior for up to hundreds of millennia, are likely able to form stable climate systems while the spin behavior is constant. Which gives the SF fraternity somewhere to set their "playground". Many studies have shown that with sufficient heat circulation in the atmosphere and/or oceans, these planets may not have a temperature dichotomy as extreme as was once thought between their day and night side It would also seem that the paper's authors have noticed the "dramatic" potential :

An illustrative example would be a planet that was previously tidally locked for a long period of time, hundreds to thousands of years, whatever is long enough that the climate has settled into a stable state. Such a planet in the habitable zone around a TRAPPIST-1-like star could have an orbital period of around 4-12 Earth days – the approximate orbital periods of T-1d and T-1g, respectively. Due to the TLSR [’tidally locked with sporadic rotation’] spin state, this planet may, rather abruptly, start to rotate, albeit slowly – on the order of one rotation every few Earth years. The previous night side of the planet, which had not seen starlight for many Earth years, will now suddenly be subjected to variable heat with a day-night cycle lasting a few years. The day side would receive a similar abrupt change and the climate state that prevailed for centuries would suddenly be a spinning engine with momentum but spark plugs that now fire out-of-sync with the pistons. In this analogy, the spark plugs and the subsequent ignition of fuel correspond to the input of energy from starlight. The response of ocean currents, prevailing winds, and weather patterns may be quite dramatic.

It's an interesting idea. Much fun to play with. The big dramtic laibility I can see is that the onset of rotation would be fairly slow, so frozen air from "dark side" is likely to be evaporating from the terminator (day/ night boundary line) as it gradually progresses into long-untouched areas ; not freshly exposed to the heat of the noon-day sun. That terminator evaporation is going to rapidly increase the heat-transporting capabilities of the atmosphere, both into the newly-lit regions and back to the newly dark regions. Which ... is exactly where the SF author can slice and dice the "science" and "fiction" parts of their business.

For perfectly good reasons, authors are very chary about receiving "interesting ideas" from the general public. Too much chance of a "plagiarism" lawsuit. Baxter suggests mailing via "c/o Christopher Schelling, Selectric Artists, 56 Planetarium Station, New York NY 10024, USA, Email: Christopher Schelling ; if his Google-fu is strong, he'll get some notification from Google that people are talking about him. Maybe. I'll see if there's any response before the end of the month. 19th - haven't heard anything yet. I'll have to get into doing the edit-before-publish thing instead of republishing as I edit.

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Some Tweets - and Toots

Hands up who loves a good B-Z reaction? No, sorry, that's unfair. Everyone loves a good - or even a bad, BZ reaction. Well, how about this one?

The Frederick lab has perfected disposal of used luminol-based ECL reagent. After the Western is developed, inject the ECL into a solution containing 10% bleach. Chemistry is awesome! pic.twitter.com/fa9z7XEQkl

— Dr. Kendra Frederick (@kendrakf13) June 14, 2018

That's not a B-Z reaction, but it is quite dramatic, isn't it? It's obviously a light-emitting oxidation reaction (10% "bleach" is a it stronger than regular supermarket bleach (my under-sink bottle says it's less than 5%), but you could get to 10% using a freezer. What are the other reagents? Byproducts or waste products from a "Western". Which is a "Western Blot Test", I think - a way of "fingerprinting" genetic material. Or, as Wiki puts it, a widely used analytical technique in molecular biology and immunogenetics to detect specific proteins in a sample of tissue homogenate or extract. Besides detecting the proteins, this technique is also utilized to visualize, distinguish, and quantify the different proteins in a complicated protein combination. That latter is pretty much where I got the "fingerprinting" idea from. This would seem to be a mixture that is used for chemiluminescent detection, but this surplus solution has clearly not reacted with the "reporter" part of the detection antibody. "Luminol" is mentioned, with this structure :

(Structural diagram of luminol molecule, a bicyclic with benzene coupled to a nitrogen-nitrogen containing ring.) So I guess getting any supply of luminol, in an appropriate solution , then injecting it into an oxidising solution, and you should indeed get this sort of display. P Ah, I thought I recognised that name - the compound is one that gets cited in every second "true crime" programme as the "magic blood detecting spray". The Luminol can react (briefly, but it can be photographed) with oxygenated haemoglobin in blood, producing this same glow.

So if I need to clean up a site from a blood splatter, a reducing agent that reacts with haemoglobin should make the SOCO's job harder. (Scene Of Crime Officer.)

Well, that's a technique I can't use after I publish this. [Shrug]

It's a fun piece of chemistry, but I doubt I'll ever have the materials to do it. If I'm ever ordering from the BDH (or Aldrich, or whoever) catalogue, I'll maybe get some Luminol, but I doubt that'll ever happen.

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The Next Generation Arecibo Telescope: A preliminary study

link

Finally nearing "up to date".

The 1960s-designed Arecibo radio telescope sufferec catastrophic failure of one of it's three support towers on December 1^st 2020. It's loss meant the loss of observational capability in three major fields

• planetary science,
• space and atmospheric sciences
• radio astronomy

The radio astronomy work can, to a significant degree, be performed at other sites (including the recently comissioned Chinese 500m Telescope, "FAST"), but few sites have the capability to transmit high power radio signals into the sky with high accuracy, which was used for radar imaging of passing asteroids, radar mapping of Venus, and studies of the Earth's atmosphere.

Proposals are now being made for a replacement to continue astronomical observations on the site. This proposed structure uses a large number (102) of identical 13m steerable parabolic dishes mounted on a separately pointable base structure about 150m in diameter. The "base plate" would deform under it's own weight (and wind loads ; Arecibo remains in hurricane territory), which the individual dishes can be re-pointed to accommodate as the telescope tracks a target across part of the sky. (The paper doesn't say "commodity satellite base-stations" - but with over 100 required including spares, that's the industry that would probably fill the order, even if the design is specific for this job.)

This approach of "many small receivers, linked" has long been used in radio telescopy. Big, fully steerable structures like Jodrell Bank and Green Bank have to some degree been superceded by large arrays such as the Allen Telescope Array and https://en.wikipedia.org/wiki/Square_Kilometre_Array . Improvements in radio sensitivity have moved the emphasis from the "light bucket" approach to improving angular resolution by widely-spaced receivers. The ultimate end of this approach is using telescopes at opposite points on the Earth for a receiver spacing of up to 12,000km. Until, of course someone puts a significant radio telescope in space.

Part of the purpose of science papers is to provoke questions. This approach makes me think - could the operations phase of the (proposed) NGAT130 (Next Generation Arecibo Telescope-130m) be brought forward into the construction phase by mounting the first 13m dishes around the rim of the "bowl" to start doing science while the tiltable platform is built within the "bowl".

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The Winchcombe Fireball—that Lucky Survivor

https://arxiv.org/pdf/2303.12126.pdf

On February 28, 2021 a bright fireball was seen over SW England, by many eyewitnesses and by a considerable number of sky-observing "fireball cameras" which allowed the rapid calculation of the fall location. The next day, 0.6kg of relatively lightly contaminated meteorite was recovered, including one bodt which fell onto a paved driveway. The number of instrumental records allowed the reconstruction of the original orbit, and also the calculation of the strains imposed on the body at the times of it's several fragmentation events. The initial mass of the meteor was estimated at 13kg, with about 4% of it's mass recovered.

The observing cameras were parts of 5 different camera networks, all 14 cameras grouped into the UK Fireball Alliance (UKFAll) (3 from SCAMP (System for the Capture of Asteroid and Meteorite Paths) ; 3 from UKFN (UK Fireball Network) ; 3 from UKMON (UK Meteor Network) ; 2 from NEMETODE (Network for Meteor Triangulation and Orbit Determination) and 3 from GMN (Global Meteor Network). Fortunately the camera networks have common standards and procedures for reporting and combining data, allowing the networks to work together in real time. Their joint PR mechanisms managed to coordinate reporting on news media so that amateurs in the fall area recognised and collected, with anti-contamination procedures, the meteorites.

On analysis, the meteorite was classified as a CM2 carbonaceous chondrite, which is a fairly uncommon type of meteorite. (Analyses continue.) The body's pre-impact orbit was moderately eccentric (e≃0.61), which with a semi-majjor axis of 2.598 AU gave an orbit that touches Earth's orbit near it's perihelion and has an aphelion near the orbit of Jupiter (0.98 and 4.18 AU respectively). The orbit was in the same direction as the Earth's, approaching it from it's trailing quarter, which lead to the relatively low impact velocity of 13.8 km/s (the Earth's orbital velocity is 18km/s, which is a more typical lower limit for impact velocity of meteors. That low closing velocity with Earth is why it experienced realtively low stresses in flight. Even so it fragmented several times in flight, each fragmentation being accompanied by a flare of the fireball.

The meteor's pre-impact orbit falls between the 3:1 and 5:2 mean motion resonances with Jupiter, which suggests how the body may have evolved its orbit before entering on it's final orbit.

What strikes me - and slightly worries me, is the number of distinct groups of fireball cameras involved. This time they seem to have had good coordination, but with recent screaming from "online communities" about "do more, do it faster, do it quicker" (Slashdot story of 2023-05-10), I anticipate it will take considerable time to tie people from this burst of enthusiasm into the necessary networks of coordination and information exchange. Then again, that noise is from "UFO-hunters", so it probably wouldn't amount to much value anyway.

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Imaging deep-mantle plumbing beneath La Réunion and Comores hotspots: Vertical plume conduits and horizontal ponding zones

I forgot to save the link, but it's Open Access.Search for "Dongmo Wamba et al., Sci. Adv. 9, eade3723 (2023) 25 January 2023"

Over the last few decades the questions in deep mantle petrology have somewhat shifted from "Do hotspots really exist?" to "What is the structure of hotspots>". In the process the image has shifted from the cartoonish idea of a single jet of hot material rising from (where? That's always been a question) to play in the underside of the crust (or lithosphere - not the same thing!), creating particular melts, and causing a circular area of thermal uplift, to the much more complex ideas expressed in this 3-d seismic tomogrpahy exercise described in this paper.

For several years, a protracted sequence of earthquakes under the Indian Ocaen island of Mayotte. I thought I'd written about the Meyotte events previously - I've certainly prepared some diagrams - but if I did, I can't find it.

Short version : there have been a lot of earthquakes under the island group of Mayotte in the arm of the Indian Ocean separating Madagascar from Africa. Lots of earthquakes. Enough earthquakes to raise very real concerns about the stability of the atoll's flanks, as well as the simple risk of unadorned ground shaking.

Mayotte is a départemnt of France, so their government have to take the threat seriously. It may be unlikely to uproot the Eifel Tower, but a major earthquake (or eruption, or sector collapse) would seriously affect, or even kill substantial numbers of French citizens (and no small number of refugees and economic migrants from across the Mozambique Channel). So of course, they French take it seriously.

One part of that taking seriously has been the establisjhment of a dense array of seismographs, which assist in locating earthquakes in the body of the volcano. But it also allows the recording of changes in seismic waves from distant earthquakes which pass through and below the volcano and are affected by changes in the rock properties. This is the essence of the subject of "seismic tomography", which acquires a very thick accretion of mathematics to deconvolve the signal from the raw seismic. But that's what computers are for.

What this paper reveals is that below the SW corner of the Indian Ocean there are conduits of relatively hot, low seismic velocity rock

• moving up from the core-mantle boundary …
• to pool at the 1000km to 600km (depth) "low velocity zone" …
• then to move up further to pool again at another "low velocity zone" …
• then finally erupt (or intrude) to (near) surface

Which is fairly conventional "hotspot" theory. But there is one problem - the vertical conduits between each storage level are offset horizontally from each other by several hundred kilometres, if not more. That definitely isn't in the conventional story of hotspots.

This diagram (from Mantleplumes.org - guess their point of view!) shows - on the left panel - the traditional view of plumes ascending more or less directly from the CMB (Core-Mantle Boundary) to the base of the crust. In the right-hand panel several "low velocity zones" (LVZs) are indicated at different levels in the mantle, associated with various levels of dismemberment of subsiding plates. In contrast, the model from this Mayotte paper postulates that the same LVZs are actually conduits for horizontal movement of magma ascending from the CMB towards the surface, potentially displacing the position of the conduit hundreds or thousands of km between each level.

In short, the plumbing store has supplied the same parts, but they're now arranged differently.

The previous diagrams have been cartoons. Now comes the actual data, rendered as a cube of [difference in seismic velocity] versus northing and easting (I'm avoiding "latitude" and "longitude" because that could get really complex where you're comparing radii that differ by a factor of 2).

What do we see here? Well, it's typical geology - obviously it bears some resemblence to the cartoon (there wouldn't have been much point drawing the cartoon otherwise …), but it's also a lot more complex. The "levels" where there is horizontal melt (heat) transfer aren't level, and the "pipes" where there is vertical melt (heat) transfer aren't vertical. The "lava lamp" appearence … well, isn't the physics in both actually quite similar. It has been a long time since I had a lava lamp, but now I'm thinking that a vacuum-walled (reduce lateral heat losses) lava lamp with 3 immiscible liquids (continuum transparent; two opaque colours) would be really intereasting. I'd put a beer on it that at least one of the offices or labs of the authors has a lava lamp of some sort.

Summary

It's a much more "realisitic" feeling model. I've always been rather uncomfortable with the "cartoon" hotspot model, because the idea of such a norrow conduit persisting for so long - as well as "how the fsck do they get started?" really seemed to ask quite a lot of Earth's materials (well, any other planet's too). But the basic idea seems to have som many things going for it too. Seamount chains ; Wrightman's triple junctions ; the Yewllowstone trace under America ... it's all very tempting.

This model makes that look a lot more reasonable. It is a much more "geologically reasonable" model. "More seismic data under other complexes!" I'd really like to look underneath the incipient rift zone of East Africa - and this can't have escaped the authors either. The Yellowstone trace, OTOH would tell us a lot more about how cells (and walls and conduits) fade away. If we we're still allowed to think about basin studies and the timing of generation in petroleum provinces, this would probably get a lot of traction there.

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HTML Learnings

Moved to "Study Notes" blog

2023-04 April Science Readings

Well, I'm still ploughing through the backlog. But progress …

Articles studied this April - some of which might go to Slashdot.

The backlog of old stuff

A quick "Funny"

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The Backlog

I get a daily mailing of new papers, and open ones that grab my attention by the title. I've got to speed up that pipeline to get through the backlog.

What have I got open on the tab list?

The Event Horizon Telescope Image of the Quasar NRAO 530 link This isn't "new" observation with the EHT, but calibration observations made back in 2017 as part of the initial runs of the radio interferomenter. "Their observed brightness temperature suggests that the energy density of the jet is dominated by the magnetic field. " - Intensity, polarisation and position of features changes. Further observations. I think I can leave this one pending.

Machine learning detects multiplicity of the first stars in stellar archaeology data link Complex study on Population-III stars, trying to work out their multiplicty from the fine details of the metallicity of thes Milky Way's "EMP" (Extremely Metal-Poor) stars. Yes, there were probably a lot of multiple, within the same range as today. Worth testing - because these stars supernovae are likely to end up beig the oldest probes into the universe since the CMB, and we need to know (or at least, test) that the stars then were similar to those we see "today" to calibrate our models on.

The Venus’ Cloud Discontinuity in 2022 link There's some weird stuff going on in Venus' atmosphere - it rotates faster (at some altitudes - than the ground. Which is ... odd. Continuing observation campaign.

Limits on Neutrino Emission from GRB 221009A from MeV to PeV using the IceCube Neutrino Observatory link In last month's GRB221009A Slashdot posting I predicted more papers. I think this was posted to ArXiv a couple of days later than that one, and there will be more in the backlog. I commented on /. that this was a (relatively rare) negative report - "we looked for Y, which we expected to see, but didn't". Valuable, but as sexy as the Ann Widdicombe range at Ann Summers.
See also : The first JWST spectrum of a GRB afterglow: No bright supernova in observations of the brightest GRB of all time, GRB 221009A, "The host galaxy appears rather typical amongst long-GRB hosts and suggests that the extreme properties of GRB 221009A are not directly tied to its galaxy-scale environment." ; The power of the rings: the GRB 221009A soft X-ray emission from its dust-scattering halo (What formed those ring-like structures presented in the composite paper, and what we can deduce from them.) ; Implication of GRB 221009A: Can TeV Emission Come from the GRB Prompt Phase? The highest-energy particles from the source probably "probe" deepest into the central "engine" of the event, and thus the whole class of events. ; GRB 221009A THE BOAT Studies the brightness of the GRB, and justifies calling it at least the "Brightest since human civilisation began."

Galaxy Zoo stuff : Galaxy Zoo: Kinematics of strongly and weakly barred galaxies ; Reanalysis of the spin direction distribution of Galaxy Zoo SDSS spiral galaxies I know "Galaxy Zoo" - do you? (Seriously - answers in a comment below, please!) It's one of the early examples of "Citizen Science", using the bulk observations of (lightly) trained amateur observers to classify (previously-made survey) images of galaxies using the human eye-brain abilities for pattern recognition. No dpoubt it'll be replaced by AI models ... uhhh, trained on Galaxy Zoo results. That's counting "angels dancing angel-counting dances on pinheads" territory. Recursion, potentially to a worrying level.
Anyway, two papers here. The first reports a moderate, neither expected nor unexpected relationship between bar strength (contrast) and rotation speed). Peculiar, but not exactly Earth shattering.
The second is just odd. Peculiar. As determined by GZ observers, presumably not interacting, the spin direction of galaxies is fairly strongly non-random (sigma 2.33~3.97). Which ... might be some larege scale structure of the universe. Or some unexpected aspect of GZ viewers, users, or ... something. What it means I have no idea, but it's definitely not expected. Watching brief.

And that's got my "Feburary pile" cleared (with a couple of exceptions). Things to do tomorrow, but maybe get March cleared over the next couple of days.

And now it's May 11th, and I haven't touched this for nearly a month.

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Redshift calculator https://wellsite-geologist.blogspot.com/2023/02/2023-february-posting-commentary.html#Redshift Something is borked, but I didn't note what.

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Funny diving.

DiverNet job advert for people to work diving in the "storage ponds" at Sellafield.

This looks like a really fun job. I wonder if the Slashdoterati will find it as amusing?

Actually, it's probably going to be a really tedious job, with masses of paperwork and endless waiting around, taking radiation readings. But the pay would be good. Maybe. [May update : the /. editors didn't bite.]

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And that's as much as I got last month.

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2023-03-29 Penrose tiling for a floor

In a discussion on Slashdot, I got into a conversation with "dargaud" (who gives his home page as http://www.gdargaud.net/). He's interested in making a floor with a "Penrose" tiling - an aperiodic tiling with (if you get it right) pentagonal symmetry. So am I. The Slashdot discussion is here (search for users "dargaud" and "RockDoctor", which is me ; but this may disapear, so I've archived the relevant bit here - it's a Box link. Seems to work though).

Both of us have been looking at doing a floor with a Penrose tiling. The Slashdot report is of a single shape that can achieve this. (I missed that from the summary, when it should have been the most prominent point. But "Meh". Bad summary writing/ editing ; or the editor thought "aperiodic tiling" was something novel, which it hasn't been since the early 1970s. Whatever, hardly news on SLashdot. Bitching about the editors is something I try to avoid, but sometimes your patience bends) From comments, this singular shape includes convex and concave sections of the perimiter that enforce Penrose's "matching rules" to enforce against getting either periodic patterns, or patterns that can't be continued to infinity.

This image

(lifted from Wiki) shows the components of a two-rhomb tiling system with "matching rules" expressed as both edge decorations and surface paintings.

The way I'd decided to do it is to use these rhombs, but without the decorations. I'd have to plan carefully to get the tiling right, before removing my marks on the prefabricated tiles. Or putting the marks on the floor, I haven't decided. The rhombs have angles of 36, 144, 36, and 144° for the "thin", and 72, 108, 72, and 108° for the "fat".

My next step was to calculate the sizes for making such tiles ("rhombs", rhombuses") with an edge of 10 cm. I've lost that calculation.

… and I've just re-done the calculation, then

… plotted them up. Note - the dimensions for the laminate tile are just a guess - and I might not use laminate in any case - maybe glue lino tiles onto sheet lino, so I can include some "bodge" allowance. But the main purpose of this picture is to show the effect of tile size on wastage, and how I'd "fit" the tile size to the actual dimensions of laminate sheet (or lino tiles) to optimise usage. Even if I decide to do it with lino, the same thinking would apply. Whatever materials I use, they're not going to be free, so I don't want to buy more than I have to.

The paper that triggered the Slashdot story was from ArXiv : An aperiodic monotile. The preprint doesn't indicate submission of the paper to a journal, but that may be normal practice in maths these decades. They have a pun in their terminology - they call their shape an "einstein" - nothing to do with a cetain theoretical physicist, but from the German "ein stein", meaning "one shape", referring to the "monotile" nature of their discovery - that this shape (actually a large, if not infinite, range of shapes) can tile the plane infinitely and hierarchically (which they claim to prove means aperiodically).

The "einstein" they present however has a seeming implicit triangular grid - which is quite distinct from the pentagonal symmetry in the Penrose multi-tile examples. So already I'm less than interested in it. My inner mineralogist wants to see pentagons! Time for an illustration, I think.

You see what I mean about the underlying triangular grid? That, I would definitely not go to the effort of building - far too pedestrian.

Their dark shaded tile looks, to me, to be composed of 4 congruent sub units, irregularly arranged ; and each of those is composed of four convex (so, relatively easy to cut) "kites" which also look to be congruent. I'm going to have to read further to find out what their geometry is, but they look like Penrose's "kites" from the "Kite and Dart" constructions from Penrose on Wikipedia :

Are this paper's "kites" (they use that term) the same shape as Penrose's? The authors specifically reference Penrose's kites in their description of the history of the problem.

Their next figure also shows the underlying trigonal (or is it hexagonal) pseudo-symmetry from their tilings. The note this themselves "Finally, we have noticed that these chains seem to impart a rough hexagonal arrangement to the hats, which is particularly clear in the triangular and parallelogram-shaped structures that are surrounded by chains."

20 pages into an 89 page paper, and I've seen nothing that looks like a definition of the "hat", or indeed, it's component "kites". I strongly suspect they're "Penrose Kites", as above, but if they say so, then I've missed the statement apart from the hint noted above. They mention that their "polykite" (also, "hat? Or have I missed something?) has sides of either 1 or $\sqrt{3}$ - which is slightly worrying because I'd expect those nuimbers to come out of 30° and 60° triangles, not those with 36° or 72° angles (where I'd expect to see lengths of 1 and [$\sqrt{5}-1$]. Distinguishing those by eye ... I'd need a definition. If it is a 30-60 structure though, that would go a long way to explaining the (pseudo-)trigonal symmetry. (Hey, I had to learn some MAthML!)

Working further, I get to Lemma A.1, where their kite is defined as having sides of 1 and $\text{exception 25:}$ (and since it's a kite, not a parallelogram, the sequence must be 1, 1, $\text{exception 25:}$, $\text{exception 25:}$. That can't be the "Penrose kite", but mut be one composed of 30°-60°-90° triangles. Which would at least make manufacturing them in large numbers relatively easy.

Figures A.8 and A.9 make the case again.

The final 60-odd pages of the paper are enumrations of possible (and impossible) neighbouring sides of the tiles, from which, I assume they can derfive their aperiodic claims.

I've no need to go further into this rabbit hole. I'm sure they've got their maths right, but aesthetically, the resultant pseudo-trigonal symmetries are not what I'm looking for. It'll be the fat-thin Penrose rhombs for me (or possibly "kites and darts", assembling those from their component triangles, which I can make by cutting strips, then cutting strips into triangles, then re-assembling.

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