As submitted ; if posted to front page, I'll modify this to reflect the editing. .
Chatter on the "Minor Planets Mailing List" (an email list for people interested in the "small bodies" of the Solar system) indicate that the Tesla Roadster polluting interplanetary space since being dumped there in 2018 has been spotted again. Telescopes in four countries reported the object. From the object's brightness, it appears to remain attached to the Falcon upper stage.
Initially, the object was misidentified as a minor planet, but once there were sufficient observations to establish it's orbit, it's identity as a "rediscovery" of "2018-017A" was established. Since the object is not natural, it is of no further interest to the astronomers and the last batch of data have been assigned to "artificial object 2018-017A, Falcon Heavy Upper stage with the Tesla roadster". Some people here might be interested though.
"Is it coming back?"
Yes, as it does every 1.525 years. This will be it's 4th return.
"Will it hit us?"
No. This time around, it'll be about 0.1 years behind Earth where it crosses Earth's orbit (4 × 1.525 − 6), which would be about 94 million km away. The closest it'll come back is about 240 thousand km away — about 2/3 of the Earth-Moon distance.
I'm not sure if Elon left the keys in the ignition. Recovering it to Earth would be an amusing trick for Bezos. There should be no legal issues since the object was clearly abandoned by it's owner. Set your diaries for 2065-ish.
If it goes onto the front page, it'll probably be edited. Which is why I've got CSS for "Insert" and "Strikeout".
I think I've mentioned FreeFall - a webcomic here previously. … No, maybe not - it's not in my tag list. Well, it's an SF webcomic that has been running for ... decades now? I think found it because got mentioned for having a use of "on the third hand" which is an obvious reference to Niven & Pournelle's "Moties". Is good. You read. (Don't be upset by the hosting site not doing HTTPS:// properly.)
In discussion of the genetics of one of the species involved ("Bowman's Wolves", below), a "rule of thumb" from ecology was mentioned, which I followed up. Someone called "Franklin" had a rule that for short term survival of a species, you need a population of at least 50 individuals, and for longer terms survival, at least 500.
I followed that logical thread, and Read The Friendly Paper. Below are my contemproaneous notes from RTFP (translated from the original PHPBB markup.
cite="MaverickMopete post_id=840776 time=1735693995 user_id=1060" at least 500 Bowman's Wolves [the gene-engineered organism], according to Franklin's 50/500 Rule.
I don't particularly remember going "what?!" on seeing that the first time (whenever that was). Now I'm going "what?!"
The idea of effective population size (my emphasis) being different for short-term and long term survival sounds vaguely right. But it also flies in the face of the experience of every species that has originated (be that sympatrically or allopatrically), and most extension-of-range developments in mobile species. Living during a period of repeated ice age versus rain age conditions, sweeping across the globe and extinguishing one species making space for another to move in ... that's very challenging. Unless the emphasised effective population size comes into play quite strongly. One wolf making it across 500 km of hostile terrain per generation being enough to couple the isolated pack of a few dozen to a larger gene pool of hundreds or thousands means that the effective population size is thousands, not dozens.
Reference : I. R. Franklin, “Evolutionary Changes in Small Populations,” In: M. E. Soulé and B. M. Wilcox, Eds., Conservation Biology: An Evolutionary-Ecological Perspective, Sinauer, Sunderland, 1980, pp. 135-149.
("Ne" is the effective population size, in contrast to the "census size") :
Before developing this argument in detail, we should ask if evolutionary change is what we want. Do we wish to conserve the elephant, or ensure the survival of its elephant-like descendants?
Speciation is discussed in Chapter 9.
(I spotted that connection immediately - but maybe that's my history of trying to inject brains into Creationists using the soggy end of a ripped-out thigh bone.)
We can distinguish between three modes of selection for quantitative traits. These are: (a) stabilizing selection, or selection against extreme values; (b) directional selection, in which one extreme is at an advantage; and (c) disruptive selection, or selection for extreme values, and against intermediates.
(a) was a big problem for Darwin, when the discrete, "atomic" (sense "undividable", not sense "components of molecules") nature of the "particle of inheritance" wasn't understood. Cue a monk in a garden in Brno. Most of the classic examples of evolution-in-action (and particularly artificial selection) operate in mode (b). Everyone who has tried hard to impress a "potential mate" only to see him/ her/ it/ them go off with "pug-ugly" has seen mode (c) in action.
Someone mentioned "uncanny valley" recently. Mode (c) poised to leap into action.
It is well known that populations which have been through a bottleneck or which have been maintained at a small population size do not show as great a response to artificial selection as do large populations.
This is one of the things that makes me dubious about the regular claims of "Mitochondrial Eve" (an unavoidable statistical event) and a human "population bottleneck" at (various times, around Toba (a major volcanic eruption about 70 kyr BP, or pick-a-number around 100 kyr BP) Both of which were certainly after the dispersal of Homo erectus across Asia, and one is almost certainly after Homo sapiens had reached towards Australia. What actually happened most likely wasn't a single, simple event. Which doesn't make for neat headlines. (Note : this paper is approaching it's 45th birthday.)
Skipping some statistics :
Effective number is decreased by increased variation in progeny number and, conversely, Ne, is maximized when all families contribute equally to the next generation.
That's one to put into your "Practical Starship Genetics" guide book. It also, effectively means making not having children illegal and immoral. "You don't own you genome, you borrow it from your grandchildren, and if they don't exist, you don't. Into the recycling tanks!" Hark, I hear the sound of a rotating Heinlein in his grave. No spreading your genes all over the galaxy!
Crow and Morton (1955) calculated from observed distributions of progeny number in a variety of species that the effective size ranged from 0.6 to 0.85 of the census number.
That gels with what I worked out from census data - in any normal year, between 10 and 15 % of women who reach menopause have had no children (and one infers the proportions are probably similar for males ; just not recorded with confidence until recently). That's using British data from a period when homosexuality was a serious criminal offence most of the time, so it's prevalence wasn't meaningfully recorded.
Unequal numbers of the two sexes. (...) A breeding population in which there are 90 effective females but only 10 effective males has a total effective size of 36, not 100.
The grave of Lazarus Heinlein would like to add the following : [rotating noises, subterranean]. Particularly since Heinlein (through Lazarus and other characters) was a great one for lecturing the readers on the genetic consequences of breeding choices.
Fluctuation in population size. If population size varies from generation to generation, the effective number is the harmonic mean:[snip maths] Suppose, for example, that a population which normally maintains an effective size of 1000 drops for one generation to 50. Then, over a ten generation interval, Ne = 345
WW1 was not that severe, but it's generation of "doomed youth" will probably have effects for generations to come. If you put it into an "American Indian etc" or "Australian Aborigine" context of repeated generations with maybe half the population of the previous generation ... yeah, that's going to be visible for generations to come too.
Immigration of unrelated individuals into an inbred population reduces the level of inbreeding dramatically
The "isolated Swedish wolves" example, or my suggestion for distributing 100 Bowman's Embryos through a slowly growing population seeded from 14 Bowman's Wolves.
Ah, this (p6) is where he gets to the "50" part of his rule of thumb. It's to keep the inbreeding coefficient below about 1% per generation. He doesn't cite any sources for his claim that Animal breeders accept inbreeding coefficients as high as a one percent increase per generation. So someone should really check on that. I don't have a, ehemm, dog in this fight, so over to someone who cares more.
Hence, Wright suggests, the splitting of species into isolated subpopulations promotes evolutionary change
What I referred to as "allopatric speciation" above, from a palaeontological point of view.
The "500" figure for his "long term survival" Ne seems pulled pretty much from thin air with a hand-waving justification that a population that size will have reduced rates of genetic drift.
Ah - next page he gives a little more justification for "500" :
Let us ignore for the present the effects of natural selection and consider only the rates of gain and loss by mutation and drift. In very small populations, the loss of variability by sampling will be greater than the gain by mutation, and there will be a net loss of variation. Conversely, in very large populations, mutation will dominate the process, and we expect a steady gain. For each trait there will be a population size at which the rates of gain and loss are equal, and there will be no net change in the existing level of variability.
He then cites some 1976 numbers for the rate of decrease of variability in a Drosophila population to support his "500" number.
It's an argument.
Considering it involves biology (the "plus or minus 10%" science), it's got about the right number of significant digits (one). It might even be "correct". For some taxa in some environments.
Selection and linkage complicate this simple picture enormously, but I will attempt to show that even strong selection does not result in dramatic reductions of additive variance.
Tease!
Hammond (1973) collected some data which illustrate the effect of small founder populations very well. He established populations of Drosophila from one, 10 and 50 pairs, and then measured the response to selection (..) over 10 generations.
(...) realized heritability (a measure of the observed change) in populations established from 10 pairs differs very little from that in populations established from 50 [pairs]. As expected, populations founded from one pair, but not maintained at this level, showed three quarters of the maximum response
The metaphorical situation of a single pregnant human female landing on a raft on the coast of Australia and thereby founding the Aboriginal population - with the addition of, say, one further genome per generation - becomes far more reasonable than some people hold it.
Finally there is the question of whether to maintain a single large population or to split the species into a number of smaller breeding units. Such decisions will be primarily made on political or ecological grounds, but the latter course seems to have distinct genetical advantages. If a species is maintained in a number of small populations, not only is the danger of accidental extinction (for example, by disease) reduced, but an opportunity for local adaptation exists which may increase the chance of ultimate survival. Genetic drift can be countered by allowing occasional migration.
Which would be assisted, in the Jeanverse [the SF universe in which this takes place] , by the relative difficulty of moving between Petri dishes using the DAVE FTL drive. [Dangerous And Very Expensive ; Faster Than Light drive]
Well that was a very worthwhile read. Sorry for monopolising this part of the thread - I find that papers stick in my head better if I make notes on them as I'm going along.
Somehow, I suspect the Mark [author of the comic] has read this paper through several times, and it has deeply influenced his world-building.
And now that I've copied this self-conversation to my own space, I can edit the original to oblivion if requested.
Is there such a thing as a PHPBB to HTML converter? Maybe.No, not really. Oh well, it wasn't too bad.
It's time to update my data on "MOND" activity. First, the what/ why/ when.
A common plaint on the Internet is that "interesting" theories are being "suppressed" by … someone, rarely specified, for reasons eve more rarely specified. The Illuminati have an interest in suppressing techniques for running your gas-guzzler on water ; Donald Trump doesn't want the kompromat tapes that Vladimir holds to become public, whatever.
A while ago I was sufficiently irritated by this to actually look at one of the genuine scientific controversies, which greatly irks the Wingnut Fraternity - how "Big Physics" ignores alternatives to General Relativity because … no clearly-stated reasons, but it doesn't take long before someone points out that Einstein was a "cultural" Jew, and therefore a prime candidate for High Wizzzard of the Illuminati etc. etc. Which irritated me, so I decided to collect some data.
If theories are being actively suppressed, then you certainly wouldn't see papers on them being published out in, uh, public, where any YT-kook can see them (if they knew how to look, or cared to). Since most physics papers get published on "the Arχiv" before they go into their respective journals-of-publication, that's an ideal place to look. (The habit is spreading too: bioarxiv.org for the biological sciences; eartharxiv.org for the Earth sciences, and probably others in fields I'm not so familiar with.
Last year I collated the last few years of research results for a number of terms related to the ever-contentious problem of gravity &emdash; how does it relate to the structure of the universe (a lot of people don't like the counter-intuitive consequences of modern cosmology &emdash; even those who don't have particular invisible sky-fairies they want to proselytise for). That collection had some problems, which I address below, but showed that the "non-standard" theories do get some attention ; just not a lot of attention. It's almost as if the "suppression of independent thought" is profoundly inefficient, and instead not many physicists find the question (or this particular "solution" to it) to be interesting or productive. The level of interest is not greatly increasing or decreasing compared to the general changes in science publication.
Data - the Kook's enemy.
Annual publication numbers for various cosmological theory terms, in Arχiv abstracts over the years.
Date
Search terms
(year-end)
Mordehai Milgrom
MOND
Non-Newtonian Gravity
MOG
dark matter
Brans-Dicke [gravity]
Date
Mordehai Milgrom
MOND
Non-Newtonian Gravity
MOG
dark matter
Brans-Dicke [gravity]
Total 1991-09-01 to 2001-12-31
22
54
54
0
3137
251
2001-12-31
4
38
46
16
538
18
2002-12-31
2
12
13
2
576
18
2003-12-31
1
22
17
2
691
25
2004-12-31
1
12
20
2
752
30
2005-12-31
2
35
22
2
876
34
2006-12-31
2
35
27
4
895
34
2007-12-31
2
49
24
2
1053
24
2008-12-31
3
61
20
3
1199
34
2009-12-31
4
51
23
6
1443
35
2010-12-31
5
50
38
4
1306
54
2011-12-31
4
60
35
5
1475
51
2012-12-31
5
42
23
6
1543
41
2013-12-31
6
56
33
3
1602
45
2014-12-31
3
58
33
8
1700
32
2015-12-31
3
40
33
5
1864
48
2016-12-31
6
51
32
6
1799
53
2017-12-31
2
55
39
17
1889
39
2018-12-31
3
48
35
16
1993
44
2019-12-31
4
55
34
8
2128
54
2020-12-31
3
51
46
19
2149
52
2021-12-31
2
43
47
9
2180
37
2022-12-31
4
63
44
11
2320
37
2023-12-31
4
85
51
24
2369
31
2024-12-31
1
59
34
11
2582
34
Notes
The term “non-Newtonian gravity” has a problem : it collects a lot of material like “non-Newtonian rheology” where gravity gets a mention ( e.g. . non-Newtonian fluids flowing on slopes). Which is perfectly valid science (Oh, I remember having to do my drilling engineering hydraulic pressure calculations on "non-Newtonian" models, on power-law models and at least one other ; every morning at 04:30 for the 06:00 report.) So, on no better grounds than that I’m going to swap that term for “Brans-Dicke gravity”, which is a term I’ve seen before. It actually pre-dates the "MOND" concept.
The Arχiv search engine has numerous complications, and I didn’t note last year’s search terms closely. Generally I'm searching in "Abstracts" (except for Mordehai Milgrom, an "Author") ; I'm searching in the "Physics(all)" space ; other terms are covered by this search link, and substitute dates and search terms as desired. That should make it repeatable over the years. Search URL : “ https://arxiv.org/search/advanced?advanced=&terms-0-operator=AND&terms-0-term=Brans+Dicke&terms-0-field=abstract&classification-physics=y&classification-physics_archives=all&classification-include_cross_list=include&date-year=&date-filter_by=date_range&date-from_date=2018-01-01&date-to_date=2018-12-31&date-date_type=announced_date_first&abstracts=show&size=50&order=-announced_date_first ” Don't forget to strip the enclosing quotes!
The different (probably) search details this year returned 3429 “dark matter" results last year, but this years searching, on the appropriate date range, returns 2369. That’s not good repeatability. So I have to re-do at least the "dark matter" results. The other terms are numberically insignificant, and I can't be bothered to repeat the search manually. Let's see what it's like next year. Having worked out the components of that search URL, I should be able to write it into a script for … wget or cURL. But how to parse the results?
Brans-Dicke theory has a Wiki page, and has been around longer than MOND. It’s interesting that this was trending slightly upwards until 2010~2014, but has been declining since.
I’ve re-done the “dark matter” queries with this year’s search parameters. The numbers are down &emdash; I was probably getting “dark” and “matter” last time, but now should just be getting “dark matter”. Or something like that. If I was doing a formal literature search, I’d probably investigate further.
Arχiv got started in August 1991, so searches from 1991-09-01 should work.
I need to get those gridlines aligned to year-ends - every 4th year or something like that.
Last year I posted a graph of the results. Same again this year, but with some more details on the axes and header.
Results
Again, "dark matter" is far and away the most popular of these different cosmologies. The figures for "non-Newtonian gravity" remain "flat" (bearing in mind that contains a significant amount of "viscosity" related research too). "MOG" (a variety of "MOdified Gravity" theories) continues to attract a little attention. My fairly-blind choice to look at "Brans-Dicke" gravity (I recognised the name, that's pretty much all!) has turned out to be interesting : until about 2010 to 2014 it was generating more publications, but since then the number has dropped, and the trend line shows that with reasonable accuracy. Those paper numbers are higher than I think could reasonably be explained by one retirement from the field ; maybe several. This is in contrast to the continuing modest rise in publication rates on "MOND".
TLDR; version : "suppression" is ineffective. Or non-existent.
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").
Ah-ha! - the "title behind the content" problem only happens when you've got multiple posts on the page. If you're on a single post, the problem goes away. Which is still undesirable, but I think it shows there's a problem with the template, not with my stuff. I only noticed at god-awful o'clock, when I was collecting data for the annual MOND update.
Oh, the problem of the "mail icon" in the footer getting stretched also happens when there are multiple posts on a page, but not with single posts. That looks like the same problem - and it's Blogger's not mine.
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).
