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Showing posts with label October. Show all posts
Showing posts with label October. Show all posts

2024-11-07

Just for a change, some EarthArχiv instead of Astronomy.

Still working the backlog, but it looks as if I've got to cut my own HTML to manage Blogger's stylistic incompetence.


Eclogites

Eclogites and basement terrane tectonics in the northern arm of the Grenville orogen, NW Scotland

Many years ago, I went walking in the highlands, all over. One place I circled around - literally - was the eclogite field on Beinn Sgritheall to the south of Glenelg, on the coast opposite Barrisdale in Knoydart. Wonderful area. And I've always been interested in eclogites, granulites, and ultra-deep metamorphics. Comes of getting started on the Lewisian foreland, I suppose.

(Oh, you've got to love the OS speelung-chokers. I'm sure they have a good reason for having "Barisdale" farm overlooking "Barrisdale Bay". Hang on! Sandaig - the place "Ring of Bright Water" was set - is in the paper's field area too. And I now have a GPX first-draft of a route for getting to the localities, "Eclogites-v1.gpx" ; that'll need some more work.)

Anyway, I spotted this article going by on EarthArxiv (which I don't pay enough attention to, I know). Even if it doesn't contain much in the way of field guides to this eclogite field, it still interests me. I'm sadly out of practice at this stuff - too long looking at (per Mike Lappin) "crustal ephemera which haven't been down to 100km for 100 Myr, and are clearly nowhere near equilibrium, so can be safely ignored. Otherwise known as the oil industry.

So, what is going on here? They seem to have evidence (structural, geochemical) that these eclogites were obducted onto the Lewisian (Laurentian, even) foreland in the Grenvillian orogeny, about 1200 Myr ago - before the Caledonian orogeny that formed most of Scotland ; before the preceding deposition of the Moinian and Torridonian (very approximate correlates) and their orogeny under the Caledonian ; back into the late assembly of the Laurentian foreland itself, these eclogites were obducted onto the foreland as an ophiolite.

Ah, approaching Real Geology : Pressure-temperature estimations obtained from various lithologies, including the eclogites, indicate peak metamorphic conditions of c. 20 kbar and 730-750°C, consistent with burial to depths of c. 70 km.. but do they give locations? "The eclogites are typically composed of garnet + omphacite + rutile + quartz (Sanders, 1989)" sounds like some fun rocks for the collection. "Omphacite grains occur with symplectites of diopside and plagioclase and are replaced around their rims by hornblende. Rutile has been replaced round the rims by ilmenite" sounds like some good hand-specimen textures are possible.

Oh goody - most of their locations are coastal. That turns an area search into a linear search. Where's my maps - sheet 32 or 33, IIRC.

Geological map of the Glenelg peninsula as far E as Ratagain, showing sampling locations for the eclogites.

I'd better go pack the tent!

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Thorne-Żytkow Objects

https://arxiv.org/pdf/2410.02896

T-Ż objects are (arguably) theoretical objects where a compact body - a white dwarf or a black hole - becomes entrained in an otherwise normal star, with lots of interesting consequences for both the behaviour of the object and it's evolution. The really interesting thing is, such a peculiar internal state may not be that obvious from the outside.

I wrote a post about these a while ago (2023-05), when some authors discussed whether or not the Sun could actually be hosting such a stellar viper in it's thermonuclear bosom. Their conclusions were that it would be hard to tell, even if the Sun had acquired it's internal parasite early in it's evolution. The energy produced by the accretion of matter onto an asteroid-mass primordial BH would to large degree replace the energy yield from thermonuclear fusion.

Obviously, other people find these objects interesting, in a train-wreck sort of way. This paper is an early version of a chapter on the bodies for an astrophysics textbook/ review forthcoming from Elsevier.

Sections cover :

  1. Formation,
  2. Internal Structure and Evolution,
  3. and their final fates,

Bearing in mind that none of these bodies have been observed (though proposals have been made - and disputed), the constraints of reality upon theory are relatively slight. More ink will be spilt!

Formation

Thorne and Żytkow originally considered the collapse of a large star's core without the normal disruption of it's envelope in nova/ supernova. However doing this without getting a large amount of "thermonuclear ash" ("metals" to an astrophysicist - any nuclei heavier than helium) on the surface of the resulting body seems challenging. And we have a wealth of spectroscopic data from many such events which do reveal various (super-)nova remnants - but no Thorne-Żytkow Objects.

Thorne and Żytkow also considered merger scenarios where a closely orbiting pair of stars, the heavier of which (most-rapidly evolving) becomes a neutron star (or black hole), and which could then inspiral into it's companion (with various requirements for ejecting material from the pair to conserve energy and angular momentum. That's a complex process, inherently variable ; hard to predict. Examples have been proposed. And disputed.

Direct collision is thought (by some) to be the most plausible formation path, particularly in the dense cores of globular clusters or molecular clouds (which the most massive stars don't have time to migrate away from before evolving into compact-body-hood. Again, the details can be complex - closing energy and angular momentum have to be accounted for.

Internal Structure and Evolution,

The main model is that the compact body has a zone near it's surface where the infall energy of the rest of the system releases large amounts of energy, producing a zone where outwards radiation is dominant, and supports the rest of the star's mass against inflow (exactly as Eddington discussed in the 1920s for formation of regular stars, leading to ideas of the Eddington limit. Beyond this "radiative zone" the star is convective as for normal stars. Potentially, with black-hole cored Thorne and Żytkow objects, the accretionary radiative zone can be surrounded by a conventional nuclear-fusing core, then it's radiative-limited zone, then the convective zone. Distinguishing these from conventional giant to super-giant stars could be very "challenging". If, however, this core material gets mixed into the upper parts of the star, that potentially is observable.

Understanding the nuclear reactions in such systems remains both controversial and challenging. Signals from both stable and unstable nuclear species have been considered.

Understanding the evolution of the objects is obviously complex. Some solutions suggest a Thorne-Żytkow object might have a shorter lifetime than the same mass regular star ; some calculations suggest the Thorne- Żytkow object could have a longer lifetime than the regular star.

And their final fates,

Like many large stars, there are multiple routes to mass loss for Thorne- Żytkow object through their evolution. The envelope mass might decrease enough that the accretionary structures can radiate through to the surface, which would rapidly radiate down to being a regular (-ish) neutron star. Or the NS could collapse to a black hole, triggering an (abnormal, ?) supernova. Many of the models produce periods of pulsation in the Thorne- Żytkow object (another potential observable?).

Fun objects, Thorne- Żytkow objects. The universe should contain such strange objects. Whether it does or not remains to be seen.

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A veritable slew of book chapters in preprint.

Wolf-Rayet stars

W-R stars are getting a deal of attention with the focus on recurrent novae and (potential) supernovæ. That's not particularly because being a WR star is associated with the SN process(-es), but because they're by definition evolved massive stars with a strong stellar wind, which means they've already run a lot of their short life. On the other hand, a powerful WR stage can lead to so much mass loss (into a large planetary nebula) that the star falls out of the window in which a SN can occur. The high mass (Mini >e; ~20 M (before late-stage mass loss) and high luminosity makes for very short lifetimes (for a 20 M star, 3.7~5.5 million years ; for a 40 M star, 2.6 to less than 1.0 million years), which in turn means the stars die (as planetary nebulae, or supernovae) still in their natal molecular clouds. Often they are part of the dismantling process of the collapsing of the cloud. But why am I trying to summarise a review paper?
The death of WR stars - there is some evidence of SN being sourced from WR stars, but other arguments that they are too compact to form SN and instead collapse directly. This latter scenario is argued for from the geometry of SNR-BH couples such as Cygnus X-1.

Small Bodies in the Distant Solar System

No, I'm not going to get into the "Is Pluto () a planet?" question. If I'd had my 'druthers, I'd have gone for an intrinsic property of planets vs dwarf planets vs other "small bodies", probably based on the "potato radius", self-rounding or something geological. but I can live with the IAU's extrinsic orbit-clearing definition. Hal Levison's "hand-waving" argument about formation mechanisms holds water too. Argument, as far as I'm concerned, over. Yes, I grew up with 9 planets in my Solar system too. I also watched the discovery of Charon, the increasing puzzlement over Pluto's minuscule size, the initial mapping by mutual occultations, and the discovery of the outer Solar System (3rd or 4th most massive element, to date, is Pluto ♇ ) ; maybe the geometrically largest. Science is a process of improving approximations to the truth, and if the solar system has a 9th planet, we've not seen it yet. That said, @PlutoKiller@Twitter.com (the social media handle of the discoverer of Eris, the most massive (known ; to-date) outer Solar system body) has been quiet lately - maybe he's found something?
Rant over. Debate not engaged with.

This is a proto-chapter for another Elsevier book. Probably not the same astrophysics book as the previous entry, but there's no law against them having multiple in production at one time.

This "key point" is one of the less "stamp collecting" parts of the field : "The sizes and shapes of Kuiper Belt objects tell us about the details of planet formation, while Kuiper Belt orbital distribution puts constraints exactly how and when the giant planets migrated."

That there are now over 3000 known TNOs brings statistics to the subject of the outer Solar system, in the same way that the Kuiper telescope brought statistics to the subject of planetary systems in general. The classical a [semi-major axis ; orbital energy] vs. eccentricity (e) plot, reveals the sculpting of the Kuiper belt by interaction with Neptune (incidentally, clarifying why Neptune is a planet and Pluto isn't), while the a vs. inclination (i) plot shows that something has been sculpting the Kuiper Belt (Outer Solar system) by dragging everything through the nit-comb of small-number-integer resonances with Neptune.

Detecting, recognising, and calculating the orbits of TNOs is a noisy, bias-prone topic. What the biases are (per instrument/ methodology), how severe they are, and how to de-bias observations towards estimating the underlying population parameters, are important topics. Once orbits have been calculated, they can be classified. But classifications can change over time, as interactions with Neptune (and to a lesser degree, Uranus, Jupiter, Saturn, potentially Planet9 [Brown, Batygin 2016] ...) lead to the orbit evolving over periods of more than a few million years ; few thousand orbits. Classification is a moving goal in many cases, and needs to be tested in all cases. Not all trans-Neptunian Objects are Kuiper Belt Objects ; there are various other classes, some of which enter the inner Solar system (e.g. Centaurs).

The composition of TNOs/ KBOs are generally only available by spectroscopy (if you can get the time on a light-bucket) or colour in different filters (if you can't get the light-bucket time). This gives a hint of evolution, from the polymerisation of surface organic matter to dark-red "tholin" mixtures. The properties of TNOs eventually tend towards those of the dust of the outer Solar system, which can be compared to the dust- and debris- disks surrounding other stars. A 2024 result from the dust-detector on the New Horizons spacecraft [Doner et al (2024), Feb.] suggests that there is more dust than models of the 2010s would suggest, pointing to the Kuiper Belt being more populous and extending further from the Sun than thought in the 2010s.

Atmospheres of Solar System Moons and Pluto

Review article on ... well, as the title says. Io excepted, these are N2 - CH4 dominated atmospheres, with the outer bodies (Pluto, Triton) developing seasonal methane frosts. Io is different - it's atmosphere is dominated by SO2 with minor SO, but these components can freeze out rapidly when Io goes into eclipse behind Jupiter. Complicated systems, worth review.

Detection prospects for the GW background of Galactic (sub)solar mass primordial black holes

The prospect of (sub)solar mass primordial black holes comes up on an almost monthly basis when people are discussing the problem of Dark Matter. Last year someone, for reasons not at all clear, speculated that the putative "Planet9" [of Brown & Batygin, 2016, as modified] might be such a "primordial" black hole. It's a pretty dead idea - if they were present in significant amounts (mass-wise), then we'd have seen them in gravitational lensing experiments (observation projects) like MACHO and OGLE. They're not(MACHO, <25% of necessary dark mass) there. To mis-quote Feynmann, a beautiful hypothesis slain by an ugly fact.

Anyway, this paper suggests that moderste mass, sub-stellar black holes (so, presumably "primordial"), particulalrly those in highly eccentric orbits, might be marginally detectable by the in-work LISA mission, and more detectable by planned missions such as DECIGO.

Back to top. And that, I think is enough for this one. Plough through more backlog now.

2024-10-25

Site re-layout ; continuing with the backlog.

Continuing to fight through the backlog

For reasons not entirely obvious, my blog "title" and description had started to overlay the top of the actual content. Not sure when that started, but I've got rid of it now. Too many options there, and it's less than clear what means what. [This seems to apply across multiple "themes" ; has blogger applied some "downdate" and broken existing things?] Nope, it's still doing it. Now the title is nailed to the window, and the posts, sidebars, etc scroll over its top.Ah - maybe if I move the "title" and "description" into the "NavBar"? Nope, that didn't work. You can't move those bits out of their containers. Switching to a "classic" theme has solved the overscrolling error. The sidebars overprint the main body, so can I fix that? OK, so now, because blogger want to put bullshit thingsd on their menu, I havev to learn even more HTML to get away from their shit. Slow. Hand. Clap. Blogger. Sod this, that's enough for today.

  • Two more chapters from the incoming Elsevier book on ... planet formation? Star Formation and Stellar Atmospheres. (Are there two books in progress? Quite possibly. Regardless, these look like a couple of edited chapters. Not final versions - one has 3 times the size of glossary as the other, which I would expect the book editors/ assemblers to address down the line.) The first volume goes from GMC (Giant Molecular Cloud - one of which will form many stars, reflecting why questions of stellar multiplicity and stellar interactions remain important - to being a "star". As gravitational and pressure forces interact, the star goes through several pseudo-equilibria. Then as the scale decreases (under an AU for the "core"), magnetic forces also become significant, complicating both accretion of matter onto the core, and ejection of matter from the core. In theory, these counteracting influences should lead to a prediction of the IMF (Initial Mass Function - the probability of stars forming with mass M1, M2, M3 … . "Should" is a big word there - we haven't got anywhere near that good a theoretical model. Unsurprisingly, metallicity has several big effects (on gas transparency ; on magnetic coupling ...). It all remains very complex.
    The multiplicity of star formation (whether a core forms on it's own, or with one, 2, 3 ... companions) becomes a major question, with theory and observation not well aligned. Which is approximately the point at which the story is passed on to the next volume. (Which I don't have a link to, yet.)
    Stellar Atmospheres are very important through all of the accretion, lifetime, and death of stars, as they buffer the interation between the "surface" of the star (itself, a complex question) and it's environment. Radiation, magnetic flux and material are some of the interacting forces. The presencve of mass flows ("stellar wind") helps make it even more complex. How complex - the table of 23 different computer codes for modelling atmosphere variations in altitude/ pressure/ temperature/ absorbance/ emission may suggest how complex.
  • Another pair of linked papers. "Irregular moons possibly injected from the outer solar system by a stellar flyby" and "Trajectory of the stellar flyby that shaped the outer solar system" are linked by assuming that there was a star (or other large body) that passed through the early Solar system. Which is a very plausible scenario - when we look at star-forming regions today, they're packed with many bodies in a small volume. OTOH, since it is so long ago (multiple revolutions of the Solar system arounf the galasctic centre ; many multiple revolution of even the most distant Solar system ovjects), it's really only a question that we can address statistically. We can get to high probabilities of such an event, but not certainty. The "trajectory" of such an imposter is even more statistical.
  • 10 September 2024 - nothing interesting.
  • "Earth’s mesosphere during possible encounters with massive interstellar clouds 2 and 7 million years ago" - The "Protostars to planets" conference proceedings I was looking at a couple of days ago mentioned - in analysis of the solar environment - that the Sun probably entered the expanding "local bubble" about 6 million years ago, and is currently approaching it's mid-point. (Corollary : the "Local Bubble" is local to us and extends in roughly equal directions in all directions purely by happenstance. Worth remembering, that ; I hadn't really appreciated it before.) Wiki says the "Local Bubble" is around 1000 ly (310-odd parsecs) in diameter, which is a large proportion of the thickness of the galactic disc. Wiki displays a map of the Solar environment to 100 pc, which purports to display the Local Bubble, but that is inconsistent with these other measurements. Regardless of that (take Wiki with a pinch of salt! - as has long been known), thisd paper is more about the atmospheric cosequences of passing through the higher interstellar medium (ISM) densities around the margins of the Bubble (and other structures). The results seem likely to be complex. Increased flux of HOX molecules to the upper atmosphere are suggested to produce long-lasting noctilucent clouds (NLCs ; OK, I can accept that) which would reduce solar radiation at the surface (OK ...) by (this paper's estimate) 7%. Which yas, would be a significant climatic forcing. But those same NLCs would also reduce outgoing longwave radiation (i.e. infrared) by Order(½) … leaving what as the climatic consequences? "More data and further work are needed". (The effects on ozone concentrations are similarly mixed, varying in distribution against height more than in total column density.)
  • "The early Solar System and its meteoritical witnesses" discusses the problem that (current telescopes can't see well through the debris discs around present-day forming stars (with inferred planetary systems), so for understanding what is happening in them is strongly influenced by the meteorite components we see in the Solar system. Unfortunately, motions within the solar system obscure the question of where a particular meteorite (let alone, it's components) originated 4.5 billion years ago, and radiometric dating to the timescale of the mixing time of a protoplanetary disc is also difficult. The paper's own cited data spans some 30 million years, when the time scale of interest is O(4 Myr).
    This seems to be one chapter of a "workshop proceedings" book. Internal placeholders ("Lodders chapter", "Schönbächler chapter", "Krot, Lee chapters") point to other parts of the proceedings. Skipping various details, a basic lesson that "At any rate, obviously, the solar nebula was not homogeneous. It may have inherited heterogeneity from the parental molecular cloud but it also developed some in situ" is reiterated. Another summmary to remember is that "since the present-day main belt [of asteroids], not exceeding a twentieth of lunar mass, is but a very partial sampling of the original population of planetesimals". Seeing (weak) evidence for 95-148 distinguishable parent bodies for meteorite samples suggests the problem of raw taxonomies. The classification they refer to (someone else's work) has 30-odd categories, some overlapping. Verily, "stamp collecting" science. While isotopic ratios and thermal histories do indicate some coherent trends in meteorite composition, not having meaningful indication of the source region of most meteorites' origin leaves the field rather hobbled. That many meteorites have internal evidence of a multi-stage formation history doesn't help.
    The bulk of the paper is a review of current planetary disk evolution modelling, from distribution of matter in the nebular disk through to planetesimal assembly, not forgetting the problem of Jupiter.
  • Oh, this sounds like fun. "Minimum Safe Distances for DE-STAR Space Lasers". "DESTAR" is an acronym where they missed (for incomprehensible reasons) the necessary "ATH" part of the acronym. The authors assert that they mean "Directed Energy Systems for Targeting of Asteroids and exploRation". Essentially, it means "build as large a laser as you can, in space, with a solar panel power supply ; then build lots more of them. They classify them on a basis of the log of the array side size in metres, so a DEATH-STAR (see what I did there?) "4" would be order of 10km on a side. (Just from the abstract, there's a challenge of cooling the laser modules - the innermost ones are going to be radiating heat through 5km thickness of laser machinery, itself radiating in similar frequencies to the particular module. Getting power in is similarly problematic at larger sizes.)
    "clearly there is the potential for such an asset to be deployed as a weapon by targeting locations on Earth" Oh hell yeah! Cynical moi? suspects that no such "Earth Protection System" would ever get off the ground without this "accidental" feature being incorporated. But yeah - put them where they're too far away to actually cause damage to Earth. (What's that Lassie? Of course you don't need to shoot asteroids out of the sky. You do your shooting years (orbits) before the final approach, while the debris has plenty of time to disperse - particulalry across the original Earth-intersecting orbital trajectory. The larger arrays they say would still be able to target Earth from the far side of the Sun, which would rather be the object of the exercise. So you'd need to have a crew onboard steering the DEATH-STAR so it couldn't target Earth.
    It may be symptomatic of the times, but that sounds like the description of a really potent Earth-targetting space weapon, manned by the "right stuff" to make sure that the wrong people don't get "accidentally" missed.
    "Accidentally Terminating Heathens" would seem to be a suitable filler for the acronym gap. "We cannot," as Dr Strangelove would put it, "allow an acronym gap to develop."
  • Fucking laptop just crashed the whole post. This is getting unsupportable. "Radial Velocity and Astrometric Evidence for a Close Companion to Betelgeuse" reports more work on understanding Betelgeuse, which suggests that it has a companion of around 2 M (from the brightness variation data), or 0.6 M when adjusted with the radial velocity data. Since the high mass of Betelgeuse limits the time available, such a low-mass core would probably still be condensing, and may not even have achieved thermonuclear fusion yet. That would contribute to - even worsen - the luminosity difference between Betelgeuse and the companion to over a million-fold difference, amply explaining why it hasn't (yet) been detected.
  • There's nothing like thinking big! "Substantial extension of the lifetime of the terrestrial biosphere". Most people don't think about it, but the slow increase in solar luminosity as helium "ash" accumulates in the star's core (the root of the "Faint Young Sun Paradox") means that, regardless of what humans do, life will become extinct on Earth a long time before the Sun turns red giant. A LONG time. One fairly ha limit is when the oceans boil - or to be more precise, when the surface temperature becomes such that the vapour pressure of surface water reaches the point that it increases the greenhouse effect to raise the surface temperature, to raise the water vaour pressure to ... a positive feedback loop ending as the bottoms of the ocean basins sizzle away the last of their water. Probably not long after (a few hundred million years), plate tectonics stop.
    That's a pretty hard limit. Our current water-vapour greenhouse warming is about 15 K, and we're worrying about anthropogenic CO2 greenhouse warming of 3~5 K. What temperature the feedback kicks in is unclear. But we probably don't have to worry about that for a couple of Gyr yet. (Whereas the Sun will go red giant in about 5Gyr.) But these authors intorduce another limit, which will probably kick in earlier. While there is still water around, the main constraint on CO2 concentrations in the atmosphere is it's absorbtion by rocks during weathering (turning silicates into silica and metal carbonates - principally calcium and magnesium carbonates). These chemical reactions are significantly temperature sensitive (the old rule of thumb, if you don't have actual kinematic measurements, is that a 10 K temperature increase will double a reaction rate), so as surface temperatures increase, the atmospheric CO2 levels will be decreased. Which will continue until there is too little CO2 for plants to succeed in fixing carbon. At which point, the biosphere collapses, pretty rapidly, as the various processes that mineralise carbon drop carbonates into the ocean trenches, and plants cannot extract CO2 from the emissions of volcanoes before the mineralising chemistry throws that back into the subduction zones.
    These authors estimate that that tipping point is about 1 Gyr in the future from today. But they also posit that this is amenable to modification. They look at the temperature sensitivity of land plants, citing various examples of modern plants that continue to photosynthesise at temperatures up to 63 or 65°ree;C and note that aquatic cyanobacteria can survive to 74°ree;C. They also mention the way that "C4" plants use an extra-chlorophyll mechanism to increase the [CO2] around the sites of crabon fixation - which is a relatively novel evolutionary adaptation compared to "C3" plants.
    Secondly, they consider the sensitivity of weathering processes to CO2 concentrations and temperatures, which are less amenable to manipulation, and the influence of soils on [CO2] (which is, potentially, amenable to manipulation). These seem to suggest that CO2 fixation by weathering is not as temperature-dependent as earlier (1992) models.
    Between the changed sensitivity of wathering to temperature, the expanded (somewhat theoretical) temperature ranges of plants, and the switch from C4 to C3 plants (which is very definitely within human manipulation), they estimate that the lifetime of plants on Earth might be closer to 1.8 Gyr then the previously estimated 0.9 to 1.25 Gyr. Which is great. As long as we, as a species, can survive the coming 0.0001 Gyr, we'll cave some prospective modifications to the biosphere to do. That coming 0.0001 Gyr, though - that's going to be a problem.
  • "The Symbiotic Recurrent Nova V745 Sco at Radio Wavelengths" Recurrent novæ are a bit of a thing for me at the moment. To occur repeatedly the event that they represent must not be so powerful as to destroy the originating system, but they are quite violent events. They are thought to be related to the formation of supernovae class Ia, where the incremental addition of mass onto a white dwarf eventually reaches the Chandrasekhar Limit. At this point, the mass is 1.44 M and the collapse releases a nearly constant amount of energy (that's a significant question), making them a "standard candle" of cosmological importance. But recurrent novæ are rare things, making it hard to study the process in detail. This paper summarises the process as A nova is a thermonuclear explosion that ignites at the bottom of a layer of accreted material on a white dwarf (WD) in a binary system. The companion star is usually a main-sequence star, but is occasionally a more evolved sub-giant or giant star. The companion transfers H-rich gas onto the WD, accumulating an envelope of accreted material on its surface. As this material is compressed, the pressure and temperature at the base of the accreted layer increase, and nuclear reactions accelerate, until conditions are reached for thermonuclear runaway. (I'm not sure all novæ follow this prescription, but that's certainly the model for recurrent novæ.)

    So, what is V745 Sco? Working the name, it's a variable star ("V") in the constellation Scorpio ("Sco"), and it was the 745th such variable noted in that constellation. When it underwent it's second nova eruption in 1989, it kept the variable star designation (well, it is still a variable star!) but went onto the (short!) list of recurrent novæ.
    The (short) list of recurrent novæ : (this will go out of date, hopefully quite soon!)
    Full name Discoverer Distance (ly) Apparent magnitude range Days to drop 3 magnitudes from peak Known eruption years Interval (years) Years since latest eruption
    CI Aquilae K. Reinmuth 8590 ± 830 8.6 - 16.3 40 1917, 1941, 2000 24–59 24
    V394 Coronae Australis L. E. Errol 17000 ± 3000 7.2–19.7 6 1949, 1987 38 37
    T Coronae Borealis J. Birmingham 2987 ± 75 2.5 - 10.8 6 1217, 1787, 1866, 1946 80 78
    IM Normae I. E. Woods 9800 ± 1600 8.5 - 18.5 70 1920, 2002 ≤82 22
    RS Ophiuchi W. Fleming 8740 ± 850 4.8 - 11 14 1898, 1907, 1933, 1958, 1967, 1985, 2006, 2021 9 - 26 3
    V2487 Ophiuchi K. Takamizawa (1998) 20900 ± 5200 9.5 - 17.5 9 1900, 1998 98 26
    T Pyxidis H. Leavitt 9410 ± 780 6.4 - 15.5 62 1890, 1902, 1920, 1944, 1967, 2011 12 - 44 13
    V3890 Sagittarii H. Dinerstein 16000 8.1 - 18.4 14 1962, 1990, 2019 28 - 29 5
    U Scorpii N. R. Pogson 31300 ± 2000 7.5 - 17.6 2.6 1863, 1906, 1917, 1936, 1979, 1987, 1999, 2010, 2022 8 - 43 2
    V745 Scorpii L. Plaut 25400 ± 2600 9.4 - 19.3 7 1937, 1989, 2014 25–52 10
    Rising by ten magnitudes is normal. That is a factor of 10000 in brightness on Earth, and presumably at the source. (Small world syndrome : the "five magnitudes =100 × " definition is due to Norman Pogson in 1856, 6 years before the eruption of U Sco noted in the table above.)
    From the paper : Four of these ten are ‘symbiotic’ binaries with giant companions (Kenyon 1986), implying that evolved companion stars may be over-represented amongst recurrent novae. The implication is that less-evolved (smaller!) companion stars are associated with recurrence times that exceed the human (instrumental) timescale. A complicating factor (still under investigation) is if both stars are WDs, then (probably) the transfer rate would be slower, and the chemical characteristics (spectroscopy!) of the SN different. A theory requiring data.
    The WDs in most recurrent novae have been observed to be massive, approaching the Chandrasekhar mass. Using the effective temperature of the WD, V745 Sco was found to have a MW > 1.3 M. The effective temperatures of the WDs in two other recurrent novae, RS Oph and V3890 Sgr also suggest high masses. V3890 Sgr has a MW = 1.25 − 1.3 M and RS Oph was found to have a MW = 1.2 M. That's a lot more than that inferred for ... oh, it was Betelgeuse's companion that I was considering yesterday - not really in the recurrent nova stakes (yet). The WD in T CrB is thought to have a mass of 1.37 M. returning to Betelgeuse's companion briefly, V745 Sco was proposed to have a brightness varition similar to that identified for Betelgeuse (510 days, versus 416 days for Betelgeuse), but both have since been ascribed to internal pulsations in the red giant, rather than orbital signals.
    All of which is good background (for me), but what is the new science in this paper? The authors report and analyse radio data collected with several instruments at different times to improve certain propoerties of V745 Sco (notably the distance and the galactic reddening extinction along the line of sight). Between eruptions, the circumstellar medium is below the (radio) detection threashold, which means it would be hard to see in a SN (it would only show in the first few days of observations).

And that's enough for this post.


End of Document
Back to List.

2024-10-24

Backlog after the Mars paper.

More backlog.

Still catching up with the backlog. for a change, I'm looking at my most-recent listing.

  • Planet Formation Mechanisms (https://arxiv.org/pdf/2410.14430) - a book chapter for something that hasn't come out yet. (Is it a proceedings volume/ review collection from Protostars and Planets VII, April 10th – 15th of 2023, Kyoto, Japan ? Lots of links on that page to recordings of the conference proceedings, such as "The Solar Neighborhood in the Age of Gaia" - now that looks a valuable seam to mine, once the current problems with downloading from YT are fixed.) Quick read ... disk-instability versus core-accretion models (which are end-members of a continuum). It all happens quickly - order of a million years, and in the middle of a dusty nebula, making it inherently hard to observe. (More data, extending into the thousands of exoplanet, improves the chances of finding examples in that 1-in-5000 time period for the Solar system analogues.) All in, that looks a very valuable resource. Time for me to watch some YT, while making supper.
    [Later] Lots of stuff over my head, so far concentrating on aspects of assembling matter into protostars. (Well the conference was titled "Protosatars and Planets", and as presented on YT, the conference seems to have worked systematicay from interstellar space down to assembling planets. So, more watching to do. Worth the investment - and when YT's download blocks are broken again, I'll be back to DL them. Probably worth it's own posting, when I've got recordings that I can pause/ rewind.
  • "Projections of Earth’s technosphere. I. Scenario modeling worldbuilding, and overview of remotely detectable technosignatures." - a bit difficult to asssess this one. The astronomical point of view is that looking into the future like this helps sharpen the focus on potential bio- and techno-signatures we could find in the atmospheres of exoplanets. Worth doing. Not sure how to assess this though. Interesting, and not terribly optimistic that their Abstract sums up the results as "Our scenarios include three with zero-growth stability, two that have collapsed into a stable state, one that oscillates between growth and collapse, and four that continue to grow. Only one scenario includes rapid growth that could lead to interstellar expansion."
    I'm not sure how to assess their methodologies, but it's one for the "futurologists" to consider (if they do anything other than navel-gazing and tea-leaf reading).
  • "The Accelerating Decline of the Mass Transfer Rate in the Recurrent Nova T Pyxidis" This just caught my eye and reminded me to check on how "T CorBor" is going (Magnitude 10.2 ; Error - JD 2460607.194 ; Calendar Date - 2024 Oct. 23.69400; Magnitude 10.2; Filter Vis.; Observer MQA. It hasn't gone yet.) In comparison to T CorBor, "The recurrent nova T Pyxidis has erupted six times since 1890, with its last outburst in 2011," - 20-odd years, which compares to the 80-year recurrence (one recurrence!, poised on tenterhooks for the second) of T CorBor ; "[...] indicates that T Pyx must have a massive white dwarf accreting at a high rate." Well, it does if there is any validity to the accreting WD model - which I've heard no serious counter-proposals against. "the magnitude decline of T Pyx from ∼ 13.8 (before 1890) to 15.7 just before the 2011 eruption" Ah, that would explain why it's less well known - you need ... at least a 150mm (six-inch) telescope to see that and do any meaningful measurements on it. In the context of T CorBor being around a month "late" for it's bookings as a TOO (Target Of Opportunity) for just about ever professional telescope in the northern hemisphere, the complexity of this stars varying recurrence rate makes the delay in recurrence all the more understandable.
    This star is inferred to have at least one feedback system, where the heat of material transferring onto the WD component inflates one side of the companion star to increase the transfer rate ... leading to more complex behaviour. T Pyx' recurrence intervals of 12, 18, 24, 23, and 44 years suggests there is a lot more complexity to it's behaviour than implied for T CorBor.
    T Pyx is a bit odd. If Wiki is right (an important "if"), then the WD has a mass of 0.7 M while the companion has a mass of 0.13M. Which puts it down in the brown dwarf margin. And the total mass of the system is 0.87 M - which is well below the Chandrasekhar limit (about 1.4 M. So the big concern is ... ? Whatever things T.Pyx has up it's binary sleeve, a type 1A supernova isn't among them. [Checking the references for that mass estimate … Uthas et al (Mon. Not. R. Astron. Soc. 409, 237–246 (2010)) do give that figure, but in a context of a WD:donor mass ratio of 5:1. That still leaves the donor as being very small, for feasible WD masses (≤ Chandrasekhar), and the total mass marginal for producing a SN.
    Odd system. Big can of worms. (I also see that Schaeffer - the guy who was headlining the "T CorBor is gonna blow!" story - has a long history publishing in the recurrent nova field. As one would hope. The data densities for nova records from the 1920s to [recent] are instructive - dozens of photometric measurements increasing to hundreds per eruption.) Moving on.
  • A cosmic formation site of silicon and sulphur revealed by a new type of supernova explosion. Everyone knows the "onion" model for nucleosynthesis in (massive) stars. Less well-known is the existence of "stripped" stars where hot massive stars lose their hydrogen-dominated envelopes, revealing a He-dominated core (Wolf-Rayet stars, particularly sub-type WN). Digging deeper (ejecting more of the envelope, one gets the carbon/oxygen shell exposed (Wolf-Rayet WC/WO stars) and their corresponding type 1CN supernovae, with their unusual sets of emission lines. This paper reports a supernova whose spectrum implies stripping all the way to expose the sulphur/silicon layer of the core. SN 2021yf is proposed to show such a star's destruction with lines of multiply ionised silicon, sulphur, and argon (SiIII-IV, SIII-IV, and ArIII with an absence of lighter element lines. Which they interpret as being the detonation of such a core stripped back well into the S-Si shell.
    Nice find. I was aware thaat W-R stars were stripped, and hot, bright (so, short-lived) stars. But I hadn't realised they were - at their extremes - taking their own cores apart. "Die young, stay pretty", on a stellar scale.

And that's another couple of days worth skim-read.

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2024-10-21

Tri-axial Mars - the Mars Kim Stanley Robinson forgot

A synchronous moon as a possible cause of Mars’ initial triaxiality

https://arxiv.org/pdf/2408.14725

This came out of the backlog. Some editing from that.

28 August 2024 - A synchronous moon as a possible cause of Mars’ initial triaxiality

Oh, that's interesting. Mars presents a lot of questions because it is the closest Earth-a-like we can study in any detail.

On the other hand, many people forget how different Mars is to Earth (@twitter.com@elonmusk - are you listening? Of course not - you talk, not listen.) Yes (FTFA), "It turns out that a moon of less than a third of the lunar mass was capable of producing a sufficient initial triaxiality." may be true, but it glosses over that Mars is now (and probably always was) one tenth of Earth's mass. Is that comparison with the Moon in absolute mass, or relative mass? In either case it is ridiculously larger than Phobos or Deimos, or their combination.

Where did this Moon go? And why?

I saw an interesting SETI "lunchtime lecture" on the Martian "hemispheric dichotomy" (N. Polar Basin vs Southern Highlands) a number of years ago. Accepting the "giant impact" hypothesis for that structure (itself a natural expectation of "hierarchical growth" [should that be "oligarchic growth"? From Wiki, The next stage is called oligarchic accretion. It is characterized by the dominance of several hundred of the largest bodies - oligarchs - which continue to slowly accrete planetesimals. No body other than the oligarchs can grow. ] - little things accrete to make bigger things - models of planetary growth), then the possibility that after the last "giant impact" the body is significantly non-spherical becomes ... well, plausible, but not guaranteed. Late-stage impacts are going to deliver a lot of energy so that the planet is effectively a droplet of a low-viscosity fluid. And you've got to have a large enough body ("Moon-size", or larger ; the Moon is about 1.25% of the mass of the Earth), close enough to affect the shape of the (slowly) cooling mass.

Time to RTFP!

"Motivation :" Mars’ triaxiality makes itself most evident through the equatorial ellipticity produced by the Tharsis Rise and by a less prominent elevation located almost diametrically opposite to Tharsis and constituted by Syrtis Major Planum and an adjacent part of Terra Sabaea Yeah, well we all know Tharsis - volcanoes, possibly still recently active. Maybe a mark of "single plate tectonics and where the heat gets out. Tharsis, volcanic peaks excluded, is about 7km above the mean elevation of the planet (or is it to a reference elevation, not a "mean" - a bit of Martian cartography I'll have to check up on) while the elevation he gives for Terra Sabaea is only 2.1~2.3 km. The author then goes on to consider the ellipticity of Mars without the Tharsis contribution (which the mappers, Zuber and Smith (1997), had also considered). Even [without Tharsis] Mars retained much of its triaxiality. - Which I'll take as read. They then propose the initiation of a "seed" triaxial component from their putative moon, later amplified by tectonic processes dumping heat and magma onto the Tharsis high point. Unfortunately, this gets rather iffy already. Mars is reported to undergo a lot more "polar wander" than Earth (justifying the horrible SF consequences of losing the Moon, and all sorts of other doom) and that the current near-polar position of the North Polar Basin and the (sub-equatorial) Tharsis bulge are near-coincidence. I don't think you can have both at the same time. I agree with this next quote - but am not blind to the problems of moons turning up then going away : The seed asymmetry of the equator was considerable if the synchronous moon existed already at the magma-ocean epoch, and was weaker if the moon showed up at the solidification stage.

Whence had it come, whither gone?

The author's title, not mine. But yes, it's a big question.

Had the impact happened during the magma-ocean stage, it would hardly have influenced the subsequent development of Mars’ global structure.

I couldn't put it more succinctly myself. See my above "droplet of a low-viscosity fluid" comment.

On the other hand, had it [a large impact] happened during the formation of crust, it may have, speculatively, left some signature - whence the question arises whether that impact could be the one responsible for the north-south hemispherical dichotomy, a theme beyond the scope of our study.

I don't think the author has seen Marinova's SETI lecture on her work, or the associated papers. Her modelling of a Polar-basin forming impact has the redistribution of 10~20 km thickness of crustal thickness from the (putative) impact site to the rest (other 2/3) of Mars' surface - which would literally outweigh this proposed minor lunar re-shaping. There's the non-trivial point too that the crust and upper mantle would have isostatically adjusted towards following the (gravitational) spheroid or (rotational ellipsoid. Rocks are not solid, even on a cold, dead planet like Mars - they creep under forces.

He doesn't really address the "whence" question - he lists some features of protoplanetary discs, and says they might be factors, while ignoring the blunt fact that most people in the field accept the really large satellites in the Solar system (Luna, Charon) are the products of "giant impacts", and this "Nerio" (some Roman mythological associate of Mars/ Ares) would fall into that category too.

What does he say about "whither"? Well, he blames it on the LHB (Late Heavy Bombardment), with a proviso that it would have to have been early in the LHB, so that later LHB impacts would overprint the expected equator-biased impacts from bits of the moon falling to Mars.

Colour me unconvinced on that front. It's plausible, but far from convincing. The whole "LHB" concept is itself rather dependent on a relatively small number of radiometric dates from a relatively small area of the Moon, all rather close to the Imbrium Basin. There are geological challenges from terrestrial observations too. It's an idea seriously needing better support (e.g. from sample-return missions from the Lunar far-side).

The remaining 27 pages of the paper are mathematical arguments which are over my head. The author obviously thinks they show that his sequence of events is mathematically plausible, and I'm willing to accept that (besides, it's plain from the reference list, that this is his field, and he's worked with many others in this area, and presummably they accept this work when they reviewed the paper. "plausible" ≠ "true".

My summary : plausible, but I don't think it's likely. Worth a read ; not worth studying the maths (which I assume is correct).


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2023-09-02

2023-09 September - 12 December Science Readings

Yeah, well for several months, I've done damned-all. Try and get back into harness. I've been thinning out the Arχiv paper listings, even if I couldn't bear to get to work on them. So let's see what remains in the pile.

2023-12-20

Over a week without doing anything. Try to get back into the habit. The HD110067 paper stuck it's nose out at me because I recognised the HD number. Which isn't normal, even for me. It's the system which was recently reported as having 6 planets at a "perfect spacing". Which is a rather problemtic description. Anyway, follow the link into the main record.

New Year

Get a few more done.

Contents

Articles studied this September to December - some of which might go to Slashdot.
Forming Asteroid Moons
MOND Count
Star Formation in the Cartwheel Galaxy
December HTML things
The "Cosmic Train Wreck" Galaxy, A520
The abundance discrepancy in ionized nebulae: which are the correct abundances?
6-planet systemis a multi-star system.
Dating of a Latin Astrolabe.
Early Galaxies initial Initial Mass Function
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2023-09 September to 12 December Science Readings.

Revisiting Dimorphos formation: A pyramidal regime perspective and application to Dinkinesh’s satellite

https://arxiv.org/pdf/2311.07271.pdf

Last year NASA hit an asteroid moon with a spacecraft to test the efficiency of momentum transfer into asteroids. Being an (astronomically) small body orbiting in an (astronomically) weak gravitational field, the (astronomically) small amount of energy the NASA can afford to pump into such a system could produce detectable effects. The "mainstream media" didn't generally understand the point of the exercise, which was not to test if there would be an effect - everyone involved was sure there would be an effect - but to test how efficiently momentum was transferred to the body. That was a very open question, because astronomers were (and still are) pretty sure that many PHAs (Potentially Hazardous Asteroids) are "rubble piles" of many smaller bodies (from dust, up to mountains) held together by their own gravity, and were expected to be very weak. So - if hit by (say) the force of a megatonne nuke, it was very unclear if 90% of the energy would go into accelerating 99% of the asteroid's mass, or if that 90% would go into accelerating 1% of the asteroid's mass, and only 10% MT go into accelerating the main part of the asteroid away for an impact situation. That's quite an important question if we were ever faced with solving the problem in the coming year.

Anyway, that was the "why" of the mission, and a reasonably useful reesult was obtained (IIRC, about 1/3 of the momentum applied stayed in the "rubble pile, resulting in the moon's orbit being changed by about 30s - which was easily detectable. But this paper in't about that - it's about how such asteroid moons can form.

Available scenarios include : forming together (in which case, why didn't the last parts of the accumulating debris go onto the larger body, with it's stronger gravity field), capture (which Darwin (George) showed is actually quite difficult, unless you've got a "third body" to take away some of the energy and angular momentum from the encounter), impact on the main asteroid (as for the Earth's Moon, most likely ; but why then are asteroid moons so common?). Or, as this paper proposes :

[An asteroid can] deposit material into orbit via landslides.

Now, there's an idea. It doesn't sound right. If the energy comes from the movement of material under gravity, how can that material get into orbit? The trick here is that this was happening while the primary was having it's spinn increased by the Yarkovsky–O'Keefe–Radzievskii–Paddack (YORP) effect, and that effectively reduces the weight of materials near it's surface (far from the centre of spin). And that is enough to allow some of the materials disturbed by such movements.

Which sounds very weird. But that is how weak the gravitational fields are on the "small bodies" of the solar system.

The paper has more work about the time sequence of events they infer leading to the formation of this moon, and in this shape. We're probably going to see a number more examples of this as the "Lucy" mission works through it's list of asteroid fly-bys.

Back to List.

MOND Count

Formation and Growth of the First Supermassive Black Holes in MOG

A while ago, I did a count of papers posted to Arχiv over the last few years of papers on the subject of "MOND" (MOdified Newtonian Dynamics") because someone had posted (again) the false claim that scientists don't look at alternatives to the main theories of science. They do get attention - just not a lot. Previously I'd searched for "Mordehai Milgrom", "MOND" and "Non-Newtonian Gravity". "MOG" is another search term to watch out for. My previous searches have looked at yyyy-12-31 as a cut-off date, so I'll carry on with that.

Hmmm, moderately interesting - at current publishing rates, Mordecai Milgrom looks likely to retire (or stop publishing - same thing, really) about 2030~31.

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Formation of the Cartwheel Galaxy

Star formation history of the post-collisional Cartwheel galaxy using Astrosat/UVIT FUV images

The Cartwheel Galaxy is one of the prettier - and weirder - sights on the sky. To the telescopic eye, one can see an outer ring of bright, bluish stars, and an inner ring of slightly redder stars around the margin where approximately the edge of the nucleus would be, and a set of slightly curved "spokes" faintly link the two main structures.

view of the Cartwheel galaxy and it's two, nearer, companions 'G1' and 'G2', about one diameter from the centre of the CW galaxy.
It's a pretty thing, shouting a really loud "How?" across the universe across to us.

The general understanding of this galaxy's structure is that another galaxy passed, nearly centrally, through the "Cartwheel" galaxy. In 1996 radio telescopy detected a discontinuous band of neutral hydrogen emission stretching from the Cartwheel towards a nearby galaxy, "G3", which is interpreted as the impacting or "bullet" galaxy. Critically, this emission structure extends beyond the other nearby galxies, "G1" and "G2". A wider view of the system than the "pretty one" shows the relationship of the galaxies: (this is an image from the DSS - Deep Sky Survey - but as a negative image) :

annotated wider view of the system, negative, with 'G3' galaxy about 5 times the Cartwheel galaxy's diameter out from it's centre

This paper reports studies on UV emissions and brightness to estimate the star-forming rates of the Cartwheel's brighter regions, and infer the time since their formation. So we now know that the galaxies were in collision at about the start of Earth's Carboniferous period, 300 million years ago. With some modest error bars.

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December HTML things

link

What got me prompted to try to get back to work was seeing a reference to an unusual bit of HTML CSS - the "rotate" property. With this, you can ... go on, guess ... rotate text (well, strictly, a division of a page) about a point.

So, naturally, I wondered, will it work in Blogger's sandbox? Let's try.

I'll start by using my handy-dandy bit of table template :

Heading Column
a Α

And now, I wrap it up in the "div-Wol-Rotate" division I've defined up in the page's style header.

div-Wol-Rotate { height: 100px; width: 200px; background-color: lightgrey; rotate: 1 1 0 60deg;

Not working. 3 axes? no Angle? No (and the bgnd-colour isn't working either) Ah, whoops, missing trailing ";" Size? Nope. Still doesn't seem to be working. Quick dive over to the "try it" sandbox at W3schools.com ... and the code above works there, but not here. Deduction : Blogger doesn't like rotation. Oh well

I picked up this question from reading Elf Sternberg's blog, about recreating the 1994 alt.sex FAQ website in modern coding. Now, I don't know how often Mr Sternberg gets people linking to the programming bits of his website, but just so he knows, from the above - people don't only read his website one-handed.

I can't claim to have fully understood the "rotate" property - the height, width and definition of the rotation axis interact in some way I need to look at to shear the image before the rotation is applied. I need to work on that. but it doesn't seem to work here, so I'll shelve it for now.

Fiddled with the CSS for HR elements though.

A bit more mucking around with tables in IMF article.

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The Cosmic Train Wreck Galaxy, Abell-520

How Zwicky already ruled out modified gravity theories without dark matter,

This 2017 paper just jumped out at me while doing the counts of "MOND" and "MOG" and "dark matter" papers while checking out the question above.

It has interesting bits. Who could resist a phrase like "The Cosmic Train Wreck Galaxy"? Not me - that's for sure. It sounds like something "fun" happened, in the sense of "may you live in interesting times", and "best observed using a telescope". Even better that it's in a context of overheated extravagant astronomers, not staid, restrained stage actors who couldn't emote if you pulled the stick out of their back, leaving splinters. Talk dirty to me, like a central 3-4 × 1013M mass clump with mass-to-light ratio 800 × M/LR☉. i don't know how dirty, but that's definitely dirty talk! (There's probably a typo - "LR☉" for "L" ; I'm sure I'll find a resolution somewhere.)

OK - how dirty are we? 800 Solar masses for each Solar luminosity? Let's see - Sol is heavier than about 90% of stars, but the decrease in luminosity with decreasing star mass is steep. A half-M star has a luminosity of 0.063 × L (about 1/16th) while at the other end of the mass scale, the luminosity ramps far more steeply than the star mass. A 20 × M star shies with luminosity 53600 × L. So, calculating the mean brightness of matter on a gelactic scale is .. hairy. It's not clear to my limited maths if it'll be a figure above or below 1 × M/L. Probably not wildly off from 1 × . So 800 × is a galaxy with remarkably little light for it's mass. Something seems to have wrecked the galaxy's mechanism for turning mass into luminosity. No wonder people noticed them (once they'd done their accounting).

The "Train-Wreck Galaxy" has 4 references linked ( 13 M. Jee, A. Mahdavi, Hoekstra et al. The Astrophysical Journal 747(2), 96 (2012).
14 D. Clowe, M. Markevitch, Bradaˇc et al. The Astrophysical Journal 758(2), 128 (2012).
15 M. J. Jee, H. Hoekstra, A. Mahdavi, and A. Babul The Astrophysical Journal 783(2), 78 (2014).
16 Q. Wang, M. Markevitch, and S. Giacintucci arXiv preprint arXiv:1603.05232 (2016).
) but the rather more accessible Wiki article suggests that later observations have picked up considerably more luminosity, reducing the seeming unusualness of the galaxy cluster by quite a lot. It's still odd, but less odd.

The other list of cosmological oddities is worth looking at too. As they phrase it, so Lambda;CDM is rightfully a good effective theory. But is it a fundamental theory? Many puzzling observations make this nonevident. :

  1. The CDM particle, the WIMP, if it exists, keeps on hiding itself 6 more years since its “moment of truth” ;
  2. One observes 19 quasars with spins aligned with their hosts large-scale structures on a scale of almost 1 Gpc (ref.10) and dozens of radiojets from AGNs aligned on a scale of 30 Mpc (ref.11) ;
  3. A ring (actually, a spiral) of 9 gamma ray bursts extends over nearly 2 Gpc (ref.12) ;
  4. the "train wreck galaxy" that caught my attention above (which may not be so weird) ;
  5. in the cluster A3827 the offset between baryonic and dark mass (ref.17) is an order of magnitude ‘too large”(ref.18) ;
  6. Puzzles in galaxies include: the brightness fluctuations in the Twin Quasar allow a DM interpretation in terms of a large halo of rogue planets in the lensing galaxy (ref.19) ;
  7. the observed satellites of the Galaxy lie in a plane, not in random ΛCDM directions (ref.20) ;
  8. the predicted transition for the most massive galaxies to transform from their initial halo assembly at redshifts z = 8 − 4 to the later baryonic evolution known from star-forming galaxies and quasars is not observed (ref.21) ;
  9. the galaxy power spectrum deduced from SDSS-III observations fits well to the stretched exponential exp[−(k/kb)1/2] from turbulence (ref.22) ;
  10. Various further arguments can be found in our investigations (refs.23,24) ;

That's an interesting list of "problems" with the ΛCDM model, while acknowledging that it is still a good model. No joy there for Archimedes Plutonium and the Electric Universe crowd of the deluded. Frankly, while they're interesting, they're not interesting enough. Just worth me noting down, to counterblast people claiming "censorship" and "suppression" of unorthodox thinking.

Why did Zwicky think you needed dark matter, not MOND/MOG, in the 1940s?

On a third reading, I still don't get the argument the authors are making. They seem to think that, for the cluster they study (Abell 1689 ; the mention of Abell 520 is just in the "problems with cosmology" section of the introduction ; it doesn't help that this is a fairly early draft, with several arguments re-written in the text.) their calculation under several generic "modified gravity" models, still need to add some non-visible mass to the system to match the observed lensing [strong ("SL" with multiple arcs for identifiable background galaxies) and weak ("WL" with shape distortion of individual background galaxies)]. Their preferred (why?, not clear) DM candidate is neutrinos. Particularly "heavy" neutrinos with a mass of ≦ 2.0 eV. Most experimental estimates for conventional neutrinos gives them a mass of ≈ 0.1 eV - a substantial difference, but some particle physics ideas produce "sterile" neutrinos in this mass range.

I think they need to make their point on Zwicky clearer - the title is attractive, attention-getting. But I can't follow their reasoning.

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Element Abundances

The abundance discrepancy in ionized nebulae: which are the correct abundances?

A long-standing question I've had is : what is the average composition of a planet (asteroid, "small body"), versus this particular surface, or an ore body. There are a lot of slightly different answers in the literature, and not a lot of clues pointing to the most-accepted (and most detailed) answers. Slightly different, but related, answers often given for this question include :

  • "What Is the Composition Of ("WICO") the Sun?" (not necessarily the same as the average planets)
  • "WICO the Sun, if you lose the H and He?" (ditto)
  • "WICO a CI meteorite? Is it the same as their parent bodies before impact heating?"
  • "WICO the Earth (including the core)?"
  • "WICO the Earth's (or any other planet's) surface?"

They're all quite similar questions, with not quite the same answers. And the differences may (or may not) be significant when you're trying to consider the changes implied by formation processes. Obviously, I'm looking for a full, 92 element composition. How it's expressed is an issue to be wary of - a short while ago I had one of those "drowning goldfish" moments when someone was talking about "atmospheric carbon di-oxide being absorbed by the lime (calcium oxide) present in basalts". It took a time to realise that he was reading the traditional geochemist's way of reporting compositions as "oxides" (e.g. 40% SiO2, 10% CaO, 10% Al2O3 …), and taking that to mean that a basalt contains grain or molecules of actual CaO, with all the chemical properties of a lump of quicklime. Which ... well, I can see why this relic from gravimetric "wet chemical analysis" of the 18th century is confusing. But it obviously can lead to profound misunderstandings. Gotta watch that banana skin.

I'm slightly surprised that my confused correspondent didn't notice that the trace elements are normally reported as "ppm of [Element]", rather than in the "oxides" presentation. I suspect I'm going to have to address this in more detail one day. It may explain a lot of confusion about geochemistry.

So, interesting paper title, given that context. Does it deliver?

OK - first thing is to see the paper as a contribution to a programme called "Planetary Nebulae: a Universal Toolbox in the Era of Precision Astrophysics" - which isn't terribly optimistic for my "geochemistry" interests. Still useful enough though - what a star spits out this gigayear is likely to affect the composition of next Gyr's molecular cloud, hence stars and attendant planets.

From TFA : "However, the heavy-element abundances derived from collisional excited lines (CELs) and recombination lines (RLs) do not align." - which is what they mean by an "abundance discrepancy". Going back to the "oxides" presentation discussion above, the technology of measurement influences the precise data collected, and how it's expressed. Specifically, since they're measuring line strengths in spectra, I'd be surprised if they presented their abundances as "oxides".

Actually, it's quite a big effect. From the paper's introduction :

However, there is a problem, and it is a big one: we are not certain about the correct abundance of heavy elements like O, C, N, Ne, collectively known as “metals”. Since the pioneering works of Bowen & Wyse (1939) and Wyse (1942), it has been known that the abundances of these elements determined from the bright collisionally excited lines (CELs) (e.g., [O III] 5007, 4959) are systematically lower than those inferred from the faint recombination lines (RLs) (e.g., O II 4649, 4650). The ratio between both estimates is known as the ”Abundance Discrepancy Factor” (ADF), and it has been found to be around a factor of 2-4 in H II regions (García-Rojas & Esteban 2007) but can reach values of more than 500 in some PNe (Wesson et al. 2003).

A discrepancy of 2~4×, but up to 500× - yep, that's a problem. But, it's an astronomer's problem, not really a geochemist's (or planetary scientist's) problem, so I think I'll just file that as a detail to watch out for.

Annnnd … the paper is discussing the various ideas for explaining those discrepancies, but not presenting an example composition for any of their target objects. Ho hum. That just leaves me with the materials I've already collected in my "compositions" collection ( http://ArXiv.org/pdf/2105.01661v1.pdf which gives Solar photosphere and CI chrondite compositions for 83 elements ; 54 terrestrial rocks from "Science Snippets" on my HDD ; … ; ; ; ) and anything I add to it. Back to the grindstone. I still don't have estimates for the average composition of the (local) universe. Granted that the outer arms of the Milky way are second (or third) generation stars, enriched by at least one (possibly two or even three) previous generations of stars burning, exploding (for the larger ones) and contaminating the (primordial) interstellar medium ("ISM", H, He, trace Li) with "metals" which change the structure and nuclear processes of the stars. Probably I'd be looking for a local Milky Way composition, a Solar system one, and maybe a composition for an estimate first generation ISM.

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6-planet system is a multi-star system.

HD 110067 is a wide hierarchical triple system

A couple of weeks ago there was a moderate amount of news fuss over the announced discovery of a planetary system containing 6 planets whose orbital periods were at small-integer ratios (2:3 ; 3:4, etc). News coverage was all over the place. Which was all very well and good, but the source paper was a deal more nuanced than the write-ups in the popular press (well colour me sideways and brush me with a Blackadder-shaped paint pot!) Most was made of the small-integer orbital period ratios - which to me (and most people) talks of the system having gone through a phase of planetary migration that carved these ratios - probably when there was some degree of "viscosity" in the system to damp interactions to some degree. (all that means is - considerable remaining gas, or many "small bodies", being present to diffuse energy and angular momentum less violently than by collisions or close approaches). The more interesting thing, to me, is how a relatively sparse set of observations were translated into "six planets". Although the reviewers at Nature must have challenged this, I'm sure they were convinced by the data in a way I can't (and am not interested) to challenge. I accept that they've got at least some of the planets adequately located.

This original paper was published in Nature, (here, titled, "A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067", which contains substantial "Supplementary Information"), but the paper was also released on Arχiv without the access restrictions of Nature (but also without the "SI"). You should be able to judge the paper on it's own merits, but the SI is probably in large part a response to the reviewer's criticisms (or their anticipated criticisms - same difference really). I'll refer to this as the "Nature paper", with the titular paper of the "triple star" system being referred to as the "Arχiv paper".

The Nature paper reports several long-period observations of the target star (HD110067 - "HD"= the Henry Draper Catalogue and a reference number) using the TESS (Transiting Exoplanet Survey Satellite) observatory in two sessions, two years apart. The first observing session recorded 4 transits (3 of which had a common spacing - indicating one planet ; one unconstrained transit). The second session recorded 9 more transits, which confirmed the first candidate (HD110067 b, period 9.113678 days) and a second (HD110067 c, period 13.673694 days)candidate observed in both sessions. Leaving 8 unexplained transit events - which was sufficient justification for observing periods on CHEOPS (CHaracterising ExOPlanets Satellite) of fractions of a day around possible repetitions of one or more of those potential objects. In considering potential observing times, the negative evidence - that neither of the TESS sessions had recorded transits except at the noted times - which constrained the possible orbital periods associated with those transits. This series of observations confirmed HD110067 d (period of 20.519 days). Those periods (bc ; cd) were both close to a "Mean Motion Resonance" (MMR) ratio of 3:2, justifying further data collection.

This is where the "chain" of logic starts to get a bit thin. There was adequate justification for targetting more observation time, and some of that justification is in the "SI" of the Nature paper. Another planet was discovered by analysis of one of the transits, for which there was an absence of a second transit in the other TESS data set. This was identified as HD110067 e (period 30.7931 days, in a 3/2 MMR with planet d) - but only on the basis of two transits. That left two unexplained transits in the TESS data. With the assumption that these represent more planets, which continue the chain of low-integer period ratios. Which is how they proposed two additonal planets, which should have been seen in the original TESS data. But the periods they should have been there were also when the Moon or Earth were also near the satellite's line of sight (TESS orbits between a little above geocentric orbit, and a little below Lunar orbit), so originally these records weren't analysed because of glare. When this study gave adequate reason for study, ... there were the expected transits, in the (rather noisy) data. So that gave confirmation of HD110067 f (41.05854 days) and HD110067 g (54.76992 days). Which is sufficient for the reviewers and for science - but it's a lot thinner than the stereotype of multiple transits per planet.

That is how future planet identifications are going to go. If we're looking for evidence of "Earth-like" planets, you're not going to get the stereotypical multiple tranists at a rate faster than 1 observation per planetary "year". So inevitably, we're going to see increasing numbers of single-transit detections, and longer chains of inference from raw observation to deduced planet (and their properties).

Some work was also done using ground-based observations, which revealed a fair amount of magnetig and radial-velocity noise in the system, but some support for the planetary system too.

The inferred planet properties are nothing wildly unusual. They're close to the star (necessary, to find multiple transits of the first few members of the chain), at average radii (of 0.0793, 0.1039, 0.1362, 0.1785, 0.2163, 0.2621 AU) all within Mercury's orbit compared to the Sun. The deduced surface temperatures (from the star's temperature of 5266 K, and the orbital distances) are high, but not extreme (800, 699, 602, 533, 489, 440 K); a short distance out from the detected planets would be the "habitable zone" of the star. The star is estimated to be about 8 billion years old - about half way through it's estimated 17 billion year lifespan, from it's 0.798 solar-mass mass. The planetary masses (5.69, <6.3, 8.52, <3.9, 5.04, <8.4) are in a range not found in the Solar system, but actually very common in exoplanet studies.

The triple-star aspect

The second, "Arχiv" paper is also an event likely to recur. While the first group had been doing their transit-based study, other data was present in already-taken databases. The Nature paper took the primary as being a single star, it had been classified as a "wide binary" since at least 2001 (references in the Arχiv paper) using positional records from 1893 to 2015 (that must be a later revision of the "Washington Double Star Catalogue" than the 2001 reference). To my moderate surprise, the listed companion is also in the HD Catalogue, and in the original numbering system (number 110106), which implies it is quite bright, quite close, and could be spectroscopically investigated at the turn of the last century. That clearly shows that the two stars are indeed, a wide binary, separated by 415 seconds of arc, which at the star's distance (32.25pc, 105.2ly, from Gaia data) translates to some 13394 AU - which is very comparable to the spearation of Proxima Centauri and Alpha Centauri A+B. To further the similarity of the two systems, both Alpha Centauri and HD110106 are double stars - though Alpha Centauri can be resolved by telescope, while HD110106 hasn't (yet).

Since these secondary stars are well out of the line of sight to the primary, with it's resonant planetary system, they don't interfere with the detection of the primary's planets. The presence of a wide binary companion (s) do raise questions about the planet-forming process around the primary, so it's a safe bet that more investigations of this system are planned. You heard it here first.

Back to List. 2023-12-20

Dating of a Latin Astrolabe

https://arxiv.org/pdf/2311.17966.pdf quote mark

This is just a piece of fun. Ha-ha, but serious fun.

An astrolabe is an astronomical observation instrument consisting of a plate (the "mater"), a targeting sight bar (the "alidade"), a "plate" engraved with the coordinates of the celestial sphere, a movable metal net ("rete") which indicates the position of various stars, and a suspension point and vertical bar ("rule", which keeps it aligned with local vertical). It can be used for surveying, for measuring the altitude of heavenly bodies (and hence, local time), and of course identifying heavenly bodies (particularly since they normally had a celestial chart engraved on one face). Mediæval users suggested that there were a thousand uses, many of which were listed in a manual on the device written by Geoffrey Chaucer.

One of these days I'm going to find one in a second hand shop (I've got a sextant somewhere a working toy) and learn how to use it.

By pointing the sight ("alidade") at an identified star, and aligning the net ("rete") to match the star's indicator to it's altitude, one can work out the local time from the celestial grids enmgraved on the plate ("mater"). Other ways of solving two knowns for an unknown can also be done with the instrument - including (for the many Islamic users) locating the direction of Mecca in order to pray towards it (the "quiblah". [Totally tangential, I wonder if that was the inspiration behind Rowling's "Potterverse" equivalent of the "Fortean times", the "Quibbler".]

That's the mechanics. The astronomy, by which the astrolabe's manufacture (or design, or calibration) date was determined is that the precession of the equinoxes (rotation of the Earth's spin axis compared to the celestial sphere) moved the position of the stars relative to the celestial grids, allowing the determination of the manufacture (or design, or calibration) to approximately 1550 (CE ; all dates are CE, not AH).

The reason I specify "manufacture (or design, or calibration)" is that once soneone has made one of these, then the additional work to make a second is relatively small, separating "design" and "manufacture" events. The way of indicating star positions (extensions of the "rete" as long pointers, with the star being at the tip of the pointer) is potentially amenable to being fine-tuned with a pair of pliers, so a 1550 design might still be modifiable for use in 1650 (or a 1450 design for use in 1550). In fact, if the "rete" were made by casting in bronze, the raw casting would very likely need some cleaning up, and adjustment because castings - particularly reticulate ("net-like" ; same Latin root) castings often distort as the cool from molten bronze to room temperature. It's very unlikely that the raw casting would have been flat to the plane of the "mater" without some tweaking.

The pictures in the paper aren't high enough resolution to see if the "pointers" have been tweaked. But I bet they have. (when I posted the full-resolution image, I looked more closely - the "rete" is made of several pieces, which look to be cast and have then been soldered together. Yep - that almost certainly needed "calibration" after soldering together. Whether that was higher precision than this naked eye instrument would have needed ... maybe not. But it's at the limit.

Just a fun bit of sideline stuff. For me. Isn't this a thing of beauty?

Figure 6: The front of the astrolabe, with a plate, the rete, the alidade (diagonal bar), the rule (vertical bar).Caption : Figure 6: The front of the astrolabe, with a plate, the rete, the alidade (diagonal bar), the rule (vertical bar).
Back to List.2023-12-21

Initial IMF

Nebular dominated galaxies in the early Universe with top-heavy stellar initial mass functions

That's a convoluted name for a relatively simple idea, with an awful lot of consequences.

As JWST has rapidly improved our state of knowledge of galaxies in the early universe, there has been an increasing tension between the inferred properties of those galaxies. What we can observe are luminosities at different wavelengths. But to convert those observations into a model of stellar populations, ages, brightnesses and interactions, we need a way to convert those luminosites into a number of stars, at a selection of brightnesses. This is not simple, because the brightness of a star does not relate simply to it's mass. The relationship is far from linear.

Which, frankly, has been known since the start of astrophotometry - the (reasonably) accurate measurement of star brightness - in the 1870s. When that was combined with positional measurement (revealing parallax, for relatively close stars, and from that the distance to the stars), and analysis of eclipsing binaries (which gives disc sizes, relative brightness in a pair, and the absolute masses of the stars in a pair), a relationship between a star's mass and it's brightness (when on the main sequence - where stars spend most of their lifetimes) emerges. But it's not a simple relationship.

In my handy-dandy pile of astronomical data and calculations, I put together a handful of ranges of mass to cover the (main sequence) brightness of stars in the Milky Way.

Stellar Mass - Brightness relation (referenced to Sol)
Star Mass (M) Luminosity (L) Main Sequence lifetime (T, Gyr)Comment
0.1 0.001 1000 Quite approximate
0.2 0.006 333 Luminosity ≃ 0.23 × (mass ratio)2.3
0.3 0.014 214
0.5 0.063 79 Luminosity ≃ (mass ratio)4.0
0.7 0.24 29
0.9 0.7 13
1.0 1.0 10.0 (solar estimate)
1.3 2.9 4.48
1.8 9.4 1.86
2.0 16.0 1.25 Luminosity ≃ 1.5 × (mass ratio)3.5
2.5 37.1 0.6739
5.0 419.3 0.1192 Gyr
7.5 1733 43 Myr
10 4743 21.1 Myr
15 19600 7.5 Myr
20 56670 3.73 Myr, Luminosity ≃ 3200 × (mass ratio)
30 84000 3.57 Myr
40 152000 2.63 Myr
50 240000 2.08 Myr
75 550000 1.37 Myr
100 980000 1.02 Myr
I have two references for this : arxiv 1710.11134.pdf and "The Astronomical Journal, 154:115 2017, Table 1" ; it's likely that the exact numbers will change with time, but not by much.

Already the lower rows of that table are decidedly uncertain. Massive stars (more than a few solar masses) typically lose more than a few percent of their mass during their evolution (through "solar wind", strong coronal mass ejections and other processes) meaning thir luminosity and lifetime will vary considerably from the initial expectation, which is based on nuclear physics. But you can clearly see that the total luminosity varies a lot more than the stellar mass. 100 solar masses of material will shine (approximately) as brightly as 100 Sol if in individual stars, but nearly 10,000 times brighter if collected into one body.

A significant uncertainty in the nuclear physics part of this model is how much non-primordial (H, He, a touch of Li) matter there is in the mix. Since nuclei like C and N take part in catalytic series of nuclear reactions at lower temperatures than without them, even small amounts of such nuclei can considerably alter the rate of energy release form the cores of medium-size stars, and hence the mass- luminosity relationship.

When all the data you have about a distant object is it's total luminosity and distance (from it's redshift), you don't have enough data to directly infer the mass of the body (galaxy) from that data. You have to, somehow, incorporate some relationship between luminosity and mass - such as the table given above. The conventional way of doing this - in the absence of any better information - is to assume that the remote object has a similar relationship to that present in the Milky Way. It's an assumption, but it's an explicit assumption, and very open to challenge. This paper challenges that assumption for high red-shift galaxies.

(It is worth noting that, because the evolution of bright stars releases non-primordial nuclei (heavier than Li) into the interstellar medium of a galaxy, it is expected that the brightness-mass relationship will change with time - and that always has been expected. Exactly how the mass-luminosity relationship changes with time remains a matter of debate though.)

This paper looks at the spectrum of the light from three of these high red-shift galaxies (GS-NDG-9422, at red-shift z = 5.943 [reference 14]; the "Lynx arc" [from "Massive Star Formation in a Gravitationally Lensed H II Galaxy at z = 3.357. reference 15 from the paper] ; and A2744-NDG-ZD4 at red-shift z = 7.88, reference 16) and sees a distinct break in the spectrum that they infer as meaning there is a lot of gas heated to tens of thousands of Kelvin, producing significant "free-bound" electron interactions. Those temperatures are a lot hotter than the hydrogen ionisation event which gave the Cosmic Microwave Background (CMB) radiation at a temperature of approximately 3000 K, allowing the inference of considerable numbers of stars of high brightness that "pump up" the galaxy's gas temperature to these levels. Which means that the "Initial Mass Function" of the galaxies is richer in heavy stars than the Milky way of today. And in turn, that means that the inferred mass of the galaxies - which had been stressing models of the evolution of the early universe would be considerably lower.

Having a "top heavy" initial mass function in the early universe will require a lot of re-calibration of models of the evolution of galaxies. But at least there is now some data to suggest in which direction, and by how much, to adjust the models.

I see that Dr Becky Smethurst has done a video-blog on this paper on her "Night Sky News" channel.

(The heaviest species detected in the spectra is argon (lines at λ4711 and λ4740 &Angstrom;, which would suggest some "silicon burning" nuclear reactions.)

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