I haven't figured out what, or why, but the site somehow acquired code for setting the title (and description) to be an overlay on top of the actual content of the page. Which is bloody annoying. And I still don't know why, but eventually I've managed to get rid of the offending coding. Back to the layout I set up several years ago ("Simple Pale").
Do I still need to re-set the image width? Nope, seems to have gone away. Trying to work out where I previously broke things (the template-appended "email envelope icon" image was stretched across the page, instead of approximately square) is just ... frustrating. I don't know if it's in my code, or in it's interaction with Blogger. somewhere, their code surrounding the "email image icon" re-set the "image width" default that I'd set in a previous code block, so only that one image (in the rest of the template) got altered.
Some footling about because Blogger doesn't allow you to have "HEAD" or "BODY" tags in the post template, but doesn't say so until you try it.
The question asked above sort of answers itself. Of course Supernovae (and other "big bangs") can move anything they impinge upon. How much is maybe a more important question.
Since the ... early 1970s? isotopic data from lunar, then meteorite, samples have shown that the early solar system had been impregnated with nuclei like 26Al, which had a short half-life (7.17*10^5 years), and so a considerable energy release (per unit mass) into the materials they impregnated. Since Al is easily incorporated into silicate minerals, it got all over the place. In the early Solar system, that was a significant source of energy, probably responsible for the (seemingly) easy melting of "small" asteroids, rapid heating of larger bodies. Then it stopped, and normal service (gravitational reorganisation ; colission ; accumulation og heat from the decay of longer-lived isotopes) was resumed. OK ; not "stopped", slowed down and rapidly became insignificant. But this 26Al was a significant source of energy that was present in the early development of the Solar system, and isn't now.
The putative source of this material, and it's associated energy, is a supernova "near" to the early Solar system in it's early days. Consequences include that relatively small bodies (asteroids 4/ Vesta, 16/ Psyche ...) have obviously melted at masses considerably lower than modern Solar system compositions would suggest.
Until the detection of "daughter" isotopes of 26Al in meteorite samples (which daughters were less abundant than in terrestrial camples), this was a pizzle. The discovery of the "daughter" isotopes moved the problem to that of how big, and when, did the supernova erupt, producing the 26Al and injecting it into the pre-Solar nebula? It's very clear that it did, and the short lives of large (supernova-prone) stars makes it un-surprising. So it becomes a standard part of "planetogenesis". An early nearby supernova is accepted as a thing these decades. (If there is a dissenting opinion, I haven't heard it expressed.)
Then come the next questions : what would be the effect of such a supernova on the materials (and their arrangement) in the early Solar system? And also, what would be their effects in later stages of the Solar system? This paper concerns itself primarily with the effects of a strong interstellar wind on particles in the Solar system (which would be a necessity for implanting the above 26Al, though this paper deals with later stages up to and including today.
Essentially, the strong wind applies a "kick" impulse to the orbits of particles. The effect of the kick is strongly related to the size of the particle being considered - a particle of 10cm or larger would be unaffected, while a particle of 1mm diameter would be given sufficient impulse to be destabilised in it's orbit, if not completely ejected from the system. Orbit destabilisation would likely result in the particle accreting onto a larger body, or again, being ejected by a close encounter. The geological record contains enough medium-lifetime nuclei (specifically 60Fe
, half-life 2.6 × 106 years) to estimate a nearby supernova rate of around 2 per 10 million years, meaning that the Solar system is frequently swept clear of it's dusty components. Including Saturn's finer rings - though their regneration from colissions between the larger bodies should regenerate the dusty component on a rapid enough timescale to explain the rings we see.
Ejection from the Oort cloud of a system ndergoing a supernova is, in passing, suggested as a potential origin for bodies like 1I/ `Oumuamua (not that that body is short of origin proposals, from the sensible to the fantastical).
I checked recent results from AAVSO at about 17:30 local time.
Star
JD
Calendar Date
Magnitude
Error
Filter
Observer
T Crb
2460647.06597
2024 Dec. 02.56597
<6.0
0.1
V
HQA
T Crb
2460647.03
2024 Dec. 02.53000
9.8
-
Vis
BRG
T Crb
2460646.96597
2024 Dec. 02.46597
<5.6
-
Vis
TRIB
T Crb
2460646.45344
2024 Dec. 01.95344
11.341
0.0048
B
DEY
Inevitably, we're under 8/8ths cloud cover here.
18:10 (JD 2,460,647.26182) Not managing to get an updated measurement listing. But that's a fifth of a day ago. (0.19 JD), 4 and a bit hours. Is there a problem in the hardware?
My "Astro-COLIBRI" is reporting an "unclassified optical transient", but that's at a Dec of 31.57° N, which is … actually, that is in the right range (25~35) for the constellation. But T Corb is at dec 25.9°, so … I'm going to have to convert between RA systems.
OK,converter written, the optical transient ("AT2024addv") was only 5 degrees off in declination - which is a plausible error, but 36° off in right ascension, which is not a plusiible error. But the AAVSO website hasn't posted any more results as of 19:15. Then Firefox crashed. [SIGH]
Anything on other astronomy news sites? S&T? Nope. Astronomy.Com ? nope. CBAT ? Nope.
Has T CorB "gone"?
It looks like that was just a glitch - some blockage in AAVSO's pipeline just while the brightest magnitude readings had been posted for ages were at the top of the list. Overnight postings eventually went back to the norm of around 10 mag (Vis). Which is what you expect, but in this case we're poised for a rapid rise cataclysmic eruption.
Oh well, I got one bit of necessary stuff built into my worksheets. Now need the reverse function.
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.
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 :
Formation,
Internal Structure and Evolution,
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.
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.
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 avs. 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.
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.
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.
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!)
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).
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.
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).
Between one thing and another (which includes my laptop deciding to power-down half-way through an OS upgrade), a week of inactivity. Fortunately, nowt published, so let's see what is in the pile.
Bottom of the list : 16 August 2024
Oh, before I go any further, T CorB still hasn't "gone". Yet.
Portability of Fortran's `do concurrent' on GPUs How to execute code on $GPU$ in a relatively transparent manner - because those who write the code may not know who is running the code, and on what hardware. - Really, that's very interesting. But is it astronomy?
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 isd 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 probbly always was) one tenth of Earth's mass. So, presenting the same data differently suddenly sounds less impressive : "It turns out that a moon of three times the relative lunar mass of Luna to Earth ..." sounds less impressive. That, and requiring a deus ex machina to take the moon off-stage before we get to see it ... unconvincing. It's plausible that the author (one-off : Michael Efroimsky, US Naval Observatory, Washington DC 20392 michael.efroimsky @ gmail.com! ; always a good sign of something that hasn't passed an in-house peer review before seeing the outside world. The author may be right, but as it stands, it's his name that he'll blacken, not his institution) is correct, but I won't hold my breath.
Maybe worth reading about the "initial tri-axility" though. Between rotational forces, and the possibility of small bodies to exhibit "single-plate tectonics" (never (??) seen on Earth), there are some interesting questions there. Wossname did 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" - little things accrete to make bigger things), then the possibility that after the last "giant impact" the body is significantly non-spherical becomes sort-of obvious. not guaranteed though - late-stage impacts are going to deliver enough energy (which cannot leak away fast enough) that the planet is effectively a drop 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. Hmmm. Before reading TFP, that's not looking very liklely. OK, I've done enough thinking on this, it's worth it's own post.
