A recent paper on ArXiv reports a novel idea about the central regions of "our" galaxy.
Remember the hoopla a few years ago about radio-astronomical observations producing an "image" of our central black hole - or rather, an image of the accretion disc around the black hole - long designated by astronomers as "Sagittarius A*" (or SGR-A*)? If you remember the image published then,
one thing should be striking - it's not very symmetrical. If you think about viewing a spinning object, then you'd expect to see something with a "mirror" symmetry plane where we would see the rotation axis (if someone had marked it). If anything, that published image has three bright spots on a fainter ring. And the spots are not even approximately the same brightness.
This paper suggests that the image we see is the result of the light (radio waves) from SGR-A* being "lensed" by another black hole, near (but not quite on) the line of sight between SGR-A* and us.
By various modelling approaches, they then refine this idea to a "best-fit" of a black hole with mass around 1000 times the Sun, orbiting between the distance of the closest-observed star to SGR-A* ("S2" - most imaginative name, ever!), and around 10 times that distance. That's far enough to make a strong interaction with "S2" unlikely within the lifetime of S2 before it's accretion onto SGR-A*.)
The region around SGR-A* is crowded. Within 25 parsecs (~80 light years, the distance to Regulus [in the constellation Leo] or Merak [in the Great Bear]) there is around 4 times more mass in several millions of "normal" stars than in the SGR-A* black hole. Finding a large (not "super massive") black hole in such a concentration of matter shouldn't surprise anyone.
This proposed black hole is larger than anything which has been detected by gravitational waves (yet) ; but not immensely larger - only a factor of 15 or so. (The authors also anticipate the "what about these big black holes spiralling together?" question : quote "and the amplitude of gravitational waves generated by the binary black holes is negligible"
Being so close to SGR-A*, the proposed black hole is likely to be moving rapidly across our line of sight. At the distance of "S2" it's orbital period would be around 26 years (but the "new" black hole is probably further out than than that). Which might be an explanation for some of the variability and "flickering" reported for SGR-A* ever since it's discovery.
As always, more observations are needed. Which, for SGR-A* are frequently being taken, so improving (or ruling out) this explanation should happen fairly quickly. But it's a very interesting, and fun, idea.
EDIT - May : I knew I'd been writing about "Thorne-Żytkow" objects (normal-ish stars which take a meal of a compact object - neutron star, or black hole, and particularly a tiny "primordial" black hole - which as a significant effect on the star's subsequent life.) recently, but I couldn't find the damned stuff when i needed it. So I've modified the titles and labels a bit.
Short-lived repeating fast radio bursts from tidal disruption of white dwarfs by intermediate-mass black holes
FRBs - Fast Radio Bursts - remain problematic. They're at isotropic distances (outside the Galaxy, randomly distributed), very energetic, but from very small source regions (because of their rapid variability). Being a new (first detected 2007), "shiny" phenomenon, they continue to attract warranted attention. Obviously much kudos will accrue to whoever comes up with a workable solution. A big problem to such a solution is that, unlike most energetic events, at least some in this class can repeat - irregularly, and more rarely regularly.
This proposed class of solutions envisages moderately common objects interacting in a moderately unusual way. Using common objects is good for an explanation - little is known about the digestive tracts of rocking-horses, since rocking-horse shit is so rare. Ordinary horseshit on the other hand … The proposal here is to take a fairly normal black hole [an IMBH - "Intermediate-Mass Black Hole" formed by stellar collapse, massing a fistful of solar masses, not a planet mass (Primordial Black Holes, PBH - still theoretical) and not a large portion of a galaxy (SMBH - Super-Massive BLack Holes). Truely a pedestrian object - we've even detected their formation and interaction in recent years, using gravity wave observatories such as LIGO, KAGRA and VIRGO.] and throw a fairly normal White DWarf (WD, wiki link) at it ; as the BH (a few km across) tears chunks off the WD (a few thousand km across) and swallows them, the torn-up remnants may well emit radiation on time scales, frequencies, and with variability consistent with FRBs.
Even better, compact bodies (Neutron Stars, IMBHs, WDs) should fairly naturally gravitate (literally, gravitate) towards similar areas such as the centres of galaxies, globular clusters etc, increasing the likelihood of interactions.
The non-total destruction of a WD in the first encounter provides a natural mechanism for the recurrence of an FRB in a particular system. The figure that describes the model implies that the outputs are sensitively dependent on the details of a particular encounter. If any significant amount of mass transfer takes place, the details of the next encounter (and thus, a repeated FRB) are very unlikely to be identical to the previous encounter.
A particular wrinkle of this model is that the material from the accreting WD should cut across the BH's magnetic field lines, which would lead to pulsations in the accretion - as seen in FRBs. Of course, other compact body mergers would also potentially suffer similar effects, which would make deciding the cause of a particular event a matter of fairly finely balanced observations. But that was probably always going to be the case. Magnetic fields are to be expected on WDs, and NSs … but how much remains "frozen into" a BH after it's mass disappears beyond the event horizon … Good question!
When I stumble across a new word (to me) in English (or any of the other languages I study), I like to learn a bit more about it. Making this sort of note helps to fix things in my memory. It's the same logic as behind my Who Said What collection - to which I have a few new things to add. Haven't touched that since April last year, so that needs a little more fettling.
What is the origin of "kudos"?
Oh, all the way from Ancient Greek κῦδος (kûdos, “praise, renown”). I'm slightly surprised not to have guessed that myself. See also, "nous"
Wasn't kudos a big element in the Illiad? Or didn't they call that "kleios"? Sigh - another one for the re-reading list. Something about Achilles saying rude things about Ancient Greek life from the perspective of being dead. So, Odyssey, not Iliad.
One of the things non-scientists frequently don't get is that scientist are continually testing their theories by looking for things, and not finding them. This is a classic of the (not so common) publication of a negative result. (More often, they negative results are incidental remarks in the "Methods" section of a paper.)
This is perfectly simple : the data from a dozen systems observed by the TESS satellite was examined for short period, high frequency luminosity variations. They didn't find any. Which doesn't mean that these systems don't have planets - any planets could be further out (requiring longer periods of observation ; or the planet's orbital planes could not intersect with Earth ; or the periods of observation could have just been unlucky. Or, indeed, the systems may not have planets.
Negative results are a bedrock of science. They're just not sexy. If your data analysis pipeline always produces a positive result, you don't know if the result is a product of external reality, or an artefact of the processing pipeline. If you get positive results with some targets, and negative results with other targets, there probably is some difference between the two systems.
Ohhh, this sounds like fun! Beats the LHC eating the Earth any day of the week. It'd cure (for certain values of "cure") Anthropogenic Global Warming as something to worry about. And that's just the title.
Where could they be going with this? Astroseismology? Or perhaps (yet another) solution to the Solar neutrino problem? Or just blatant redneck-baiting (I have a sudden image of modifying the DREADCO "buttered toast/cat" perpetual motion machine to run off the inexhaustible indignation of rednecks about things with too-long words. Cynical? Moi?)
So, speculation aside, let's RTFP. Starting with the author list - three long, not an Avi Loeb solo lunacy special (sorry, that's being cruel ; Loeb's lunacy is generally well reasoned.), enough people there to keep somewhere in contact with reality. No names I recognise. Three institutions. None of the strong indicators of the ... fringe.
AbstractThere is probably not a black hole in the center of the sun. Despite this detail, our goal in this work to convince the reader that this question is interesting … Oh, it's one of those papers! OK, let's play!
After introducing the idea of a Hawking star (which has an asteroid-mass black hole 10-16~10-10×M☉ accreting internally in addition to normal nuclear fusion, the authors justify modelling it's evolution in some detail.
The assertion that "Despite the claimed constraints, [primordial black holes ("PBH"s, in the mass range cited above)] remain a compelling dark matter candidate for several reasons" is a bit of a surprise to me. I thought that had been excluded by OGLE, MACHO and the like, but maybe I wasn't paying close enough attention. Meh. Accepting that assertion - because it sounds a real fun idea for testing redneck PM machines - how do these authors think the presence of an accreting PBH would affect the evolution of a solar-mass star?
This sounds somewhat familiar. Did I RTFP, without making notes? Naughty Aidan! Or maybe I read one of the papers they cite - several earlier in 2023. This argument "Stars are unlikely to capture PBHs after formation. A PBH with finite velocity and falling from infinity will be accelerated up above the escape velocity and rapidly transit the star." sounds very much like an argument I made on Slashdot not-long ago. Contrary to the Physics of Star Trek ("many readers", as the authors … politesse it), the accretion of PBHs isn't an all-enveloping maw, but strongly limited by the size of the event horizon. The 10-10 M☉ PBH would have a radius of about 30000 pm while the 10-16 M☉ PBH would have a radius 0.03pm. For comparison, the (Van der Waals) radius of a hydrogen atom is about 120pm. So the number of atoms that will be absorbed at a time is in the order of zero to a few million - in the order of 10-20 kg per position. (That's my estimate. Their models, incorporate compression and gravitational radius to give a (reasonably simple) expression for the luminosity in L☉ (incorporating BH mass accretion rate (M☉/yr) and radiative efficiency (dimensionless).) Their model give accretion rates 10-9 to 10-23 M☉/yr I can't meaningfully assess the plausibility of these numbers, but a rate of 10-9 would have consumed the Sun 3.5 billion years ago. Over those accretion rate ranges, the inferred luminosities due to the BH are well below 1% of Solar luminosity - which would be within the "noise" in nuclear fusion models, given uncertainty about core metallicity and physical conditions. In short, on luminosity grounds, we can't rule out a present-day in-Sun accreting PBH.
As Telly "Kojak" Savalas used to sing, "If a picture paints a thousand data points …", so here's the graphs. Zoom in to read the axes. Their model changes behaviour (convection-limited to radiation-limited) in the middle of the MBH range considered, but still leaves Sol as not-excluded from being a Hawking star.
Section 3 of the paper examines variations on this "toy" model, including how convection pressure or radiation pressure ("Bondi" or "Eddington" domains) throttles accretion onto the BH. Two main points stand out :
The overall luminosity (and evolution over time of luminosity) are not greatly changed by the presence of the BH ;
but, the interior of the star is considerably better stirred by the BH, and this potentially could yield a measurable signal by astroseismography, and the early mixing of the core of accumulated fusion products (for a Solar mass star, essentially helium) into the outer body of the star.
The larger BH mass models cause the end of nuclear fusion at ... well, not far off the Sun's present age. Which is exactly the reason that "Hawking stars" were proposed as a "solution" to the "solar neutrino problem" in the 1970s. (The correct solution is that neutrinos have mass, and so can experience time, and so can oscillate "flavours" during their flight from Sun to neutrino telescopes on Earth. There isn't a "solar neutrino problem" now.)
The "Kippenhahn" diagrams (Figs 2 below and 4) are a nice way of summarising the evolution of stellar structure with time. I'd not met them previously. Wiki doesn't use these, but they do allow one to visualise and compare evolutionary tracks well. I suspect they'll appear at some point.
Note that the radius and luminosity vertical scales are logarithmic. The final size of a solar-mass BH is less than one-millionth of the star's radius for most of it's evolution. (If you wanted to go to longer timescales, you might make the time axix logarithmic, and a lot of Kippenhahn diagrams around the explosion of supernovae do exactly that. But these don't - just a linear time axis.
Figure 4 uses a different time scale to figure 2 : decreasing time to stellar destruction, from billions of years to the last few seconds. Things happen fast at the end.
And despite my warning above about logarithmic scales, I've slipped up above where I said that overall phenomena are not greatly changed by the BH. The authors say Once in its post-main sequence phase the Hawking star becomes fully convective and slowly swells over multiple Gyr to about 10 R☉ and about 10 L☉ causing them to appear as a sub-subgiant star, joining a relatively sparse population on the HR diagram. This phase of stellar evolution is qualitatively insensitive to the initial seed mass, and lasts for multiple Gyr in our simulations.
That's somewhat smaller but longer lasting than the typical solar-mass red giant phase, so you might be able to find Hawking stars in the lower-luminosity "sub-giant" area of the Hertzsprung-Russell diagram. A moderate difference, but it might be enough to perform a pre-cut on candidate Hawking stars. (Proposed TZOs have been reported from exactly this sort of search.)
Getting into the summary, indeed the authors consider astroseismology as a potential way of detecting such stars due to the fully-convective nature of the star. Another good question : Are there X-ray transients associated with stellar destruction that are distinct from other accreting binary systems, and if so, what are the lifetimes of this transient?
It's a fun subject, and it's got lots of potential for ha-ha-but-serious blowing of minds. And Hollywood is absolutely going to love the idea of the Sun being eaten from the inside by a BH. OK, They'll have to invent some pseudo-physics for James Tiberias Hulk and Spock Man to save the universe (well, Earth) with. But fun nonetheless.
This is strongly related to this post I made a few months ago.
Who doesn't love a bit of random destructiveness at a suitably large range? In the other carriageway for a little car bump ; in a different part of the galaxy for slightly bigger bangs, as discussed here ; in a galaxy far, far away for whatever causes Gamma Ray Bursts. This is medium-scale rubber-necking.
The recently published 6-planet system in (I can still remember the "phone number"!) the HD 110067 system (which has also been reported to be a widely-spaced multiple star) is very much the sort of system they're talking about. Though I don't think they mention it by name.
Why does this class (size range) of planets deserve separate treatment (from "rocky" planets, "small bodies", "Jupiters" (hot or not) and bigger bodies? FTFAbstract : For sub-Neptunes, the dominant type of observed exoplanets, the planetary mass is concentrated in a rocky core, but the volume is dominated by a low-density gaseous envelope. For these, using the traditional sticky-sphere assumption is questionable. While they can get mergers (for certain ranges of energy and impact factor), loss of large amounts of atmosphere are also a common outcome (which doesn't really have an analogue in smaller collisions, and complete disruption of both impactors is also common. That latter might suggest that growth of planets rather stalls in this mass-range, leading to the sub-Neptune group being the commonest type of planet discovered. (Though how much of that is a discoverability issue remains open.)
Rather than the more common computational strategy of using an array of different test objects, they only consider one pair of planets (masses m1,2 = 4.51,7.55 M⊕, radii r1,2 = 3.56,3.69 R⊕) around a sun-like star. But they inspect the parameter space by putting the two bodies in an unstable pair of orbits, then letting them evolve. With computational noise, that generates a … realistic (hmmm - questionable?) range of impact conditions for investigation. Unusual strategy, but I can see reasons for using it.
Those "test planets" are 9.99 % and 15.0 % of the Earth's density. I guess those numbers aren't so random as they look. 3:2 ratio of masses too. I wonder if they "select" from the variety of impacts they get : yes, they select on vimpact÷vescape. And high values of vimpact÷vescape lead to complete disruption of both planets - now that shouldn't be a surprise.
Here's another non-surprise. The star would get in the way of studying the interactions of the planets, so We treat the host star as a non-interacting point-mass particle, exerting only gravitational influence over the planets. If a particle approaches within one solar radius of the star, it is accreted into the star, conserving mass and linear momentum. Again, perfectly reasonable, but it's fun to see people saying it. hubris, thy name is throwing planets at each other for a living. Must make for fun dinner parties. Or am I channelling Rick'n'Morty from the telly? (episode: "The ABCs of Beth" - hey, the Krootabulan male has an appropriate three nipples!).
Hmmm, this description of the planets is … not over-detailed : We assume that 15% of the total
planet mass is in the H-He envelope, and the rest is in the iron core and rocky mantle in 30 : 70 ratio. We truncate the planet profile at a negligible density of 0.01g cm−3 and consider this as the planet’s surface. It's not wildly different from "Earth". But using an Equation of State (EOS) for a granite to describe a mantle? Are there no suitable peridotite EOSs?
More hubris in the planet-smashing community : We tackle [problem] by utilizing StarSmasher’s ability to handle unequal mass particles. yes, that is the name of one of their software packages, which they use for smashing stars together. But it's obviously a game's name. Sick! They're sick, I tell you!
OK, I learn something new every day. Today is the use of a CGS pressure unit, the "barye" (symbol "Ba"). Which is 0.1 Pascal (SI), a millionth of a bar (non-SI). That's unhelpfully obscure. I read quite a bit of astronomical work (and specifically, planetary science), and I had to look that up. Not a helpful choice of units - but probably also in "progress one funeral at a time" territory. The pressure and density profiles in Fig 2 are otherwise useful - yes, these are very different planets to Earth ("terrestrial" planets) and Jupiter (gas giants, see for example, the Juno data about Jupiter in Figure 1 of this Icarus paper of 2022). At the limit, these sub-Neptune models start to approach the "dilute core" models for Jupiter, but that theory (and the disk instability formation model underlying it) are moving into the realm of theory, not (Solar system) reality.
All that comment on the work of the paper, and I finally get to the Results. They're not too surprising : they get three types of outcome : "Hit and Run" (the most common ; two planets at the end ; small mass transfer, mostly in the atmosphere component) ; "Merger" (one planet, and some debris) ; and "Catastrophic" (no large fragments of either planet result ; high mutual velocity compared to escape velocity). The boundaries between "Hit and Run" and "Merger" are rather blurred, as different workers seem to use different degrees of mass loss (to the star ; to distribution away from the "inner" planetary system) to classify interactions. "Mergers" can lose up to 40% of the two planet's mass, and "Hit and Runs" can lose up to 25% of the system's mass. Which is not exactly a trivial consequence. "Mergers" that loses 40% of the mass of the planets could largely "stall" planetary growth at the "sub-Neptune stage" without there being a meaningful "reason" for sub-Neptunes to be favoured over (say) Jupiters. Which is rather less significant than the raw observational data might seem to suggest.
On a regular basis one hears assertions that "Big Science suppresses non-standard theories" - often followed up by "Free energy" schemes, Climate change scepticism, Anti-vaccination screeds and the like. It's a feature particularly of Slashdot, but more generally of the Internet. If I "did" Facebook, I'd probably cite them too. Kooks are everywhere and are vocal, and they love a "my voice is being suppressed" narrative.
So, a few months ago, I conducted an (admittedly crude) survey of a "controversial" idea in "non-standard" science using Arχve. It was nothing complex (I searched for various terms ["Mordehai Milgrom", "MOND", "Non-Newtonian Gravity", "MOG", "Dark matter" in Arχve's database (anywhere in article title, abstract, or body text, or figures) from Jan 01 to Dec 31 for each year, recording the counts. And now, it's time to update the numbers. They're not good reading for the conspiracy-of-suppression" theorists (well, is any reading good for them? It's not as if they like actual evidence).
Date of search
Mordehai Milgrom
MOND
Non-Newtonian Gravity
MOG
Dark matter
1991 - 2001-12-31
75
1072
735
180
43348
2001-12-31
4
38
46
16
3404
2002-12-31
2
12
13
2
693
2003-12-31
1
22
17
2
765
2004-12-31
1
12
20
2
885
2005-12-31
2
35
22
2
1005
2006-12-31
2
35
27
4
1068
2007-12-31
2
49
24
2
1179
2008-12-31
3
61
20
3
1329
2009-12-31
4
51
23
6
1635
2010-12-31
5
50
38
4
1586
2011-12-31
4
60
35
5
1643
2012-12-31
5
42
23
6
1765
2013-12-31
6
56
33
3
1802
2014-12-31
3
58
33
8
1986
2015-12-31
3
40
33
5
2123
2016-12-31
6
51
32
6
2150
2017-12-31
2
55
39
17
2239
2018-12-31
3
48
35
16
2231
2019-12-31
4
55
34
8
2419
2020-12-31
3
51
46
19
2525
2021-12-31
2
43
47
9
2651
2022-12-31
4
63
44
11
2836
2023-12-31
4
85
51
24
3429
How long is it since I made a snide comment about conspiracists and their data aversion? Too long. See table above. For those who aren't familiar with the field, "Mordehai Milgrom" is a prominent researcher in "modified gravity" ; "MOND" is a popular theory of "modified gravity" ; "MOG" is a different such theory ; "non-Newtonian Gravity" is more general term for the field ("Newtonian Gravity" being the "Big Science" conventional theory in favour of which all the other theories are being suppressed for (whatever) reason(s) ; "Dark Matter" is just there for a marker of overall theoretical activity in astronomy.
Lots of data. Would a picture help?
Much clearer. Publications in these two particular theories of non-Newtonian gravity have continued to happen at comparable rates to general astronomical activity, though the relative popularity of these two theories varies a little, "MOG" having picked up in the last few years. Mr (Professor? Probably.) Milgrom continues to publish at a fairly consistent rate - which isn't so surprising, since he's been doing so for about 40 years.
That's not the sign of a field of research that is being "suppressed", "forced underground", or even "harmful to researcher's careers". It's a sign of a relatively unpopular topic within a field. Now, "unpopular" may not be a particularly nice state to be in (anthropomorphising "theories"), but it's not a sign of effective suppression. Effective suppression is samizdat publication on midnight press runs, and the occasional publisher's head boiled in tar and spiked over the entry gates to Physics & Astronomy Departments pour encourager les autres (a short-form Voltaire-ism [Candide, ch.xxiii]; the long form is darker than many people realise.)
Having done the leg-work, I'll continue to update the data file yearly (until I get bored). If you think I should be looking at different data, that's what the "Comments" are enabled for.
What caught my attention about this? Well, "influence on Solar System bodies" means something really close, but the HD catalogue is of relatively bright stars. Just from the number, I'd think - that is likely a star about 7th magnitude (to 6th magnitude - naked eye limit - there are about 6000 stars). So ... that's not a normal combination. "Attention grabbing", as a newspaper editor might say (followed by Shome mishtake, shurley? from Lord Gnome).
The abstract is more informative : In the latest Gaia third data release one can find extremely small proper motion components for the star HD 7977. This, together with the radial velocity measurement lead to the conclusion that this star passed very close to the Sun in the recent past. Ohhh, right. That's a fun one. See my choice of title. Next question - does the WWW (Wonderful World of Wiki) know about this? Yes. No significant additions needed there.
This paper is about how much effect the passage of such a star (see 'properties' table) has on Solar system bodies, and particularly Long Period Comets (LPCs, because they're relatively loosly bound to the Sun). It's not immediately obvious that passing a Solar mass through the Solar system would have a big effect - the star is currently 250 LY away making for an average speed of 1 LY every 11,200 years. 1 LY is a reasonable approximation to the outer edge of the Oort cloud of LPCs. (Buried in the paper, they imply their "edge" to the oort cloud is at 0.5 pc, which is 1.6 LY. Meh.) More correctly, I should be talking about the sun's Hill sphere. But that's more complicated (partly because for a small "miss distance", the Hill sphere becomes very small. Guess I'd better RTFP.
My inference of brightness from the low HD-number is fair. SIMBAD has 13 identifiers for it, only 3 from GAIA. It's brightness is (as normal) variable across different colour bands, from 9.63 in the B band to 8.89 in the G band. It is situated in Cassiopeia, so is circumpolar from most of Europe and North America. The record has astrometry as far back as 1840 - pre-photographic - which cannot be ignored. The GAIA data releases have a low uncertainty, but they assume the star is a single body. If it is multiple bodies whose images overlap, differently during different observations, then the positional uncertainty could be much higher than the relatively short time span of GAIA observations can detect. Because of this, and the star's brightness, visual and older photographic data must be considered too. (Table 3) Argelander catalogued the star in 1842 and 1875 - at different declinations, from different locations (Finland and Bonn, when he was compiling the Bonner Durchmusterung where it is catalogued as BD +61 250. Further observations were recorded in 1903 (whose plates were re-measured by the author team),the 1920s, 1930s, 1940s and 1950s, then a hiatus until the 1980s, 1990s, 2000s and then the various satellite data. None of the data shows the star to definitely be a multiple star, but the multiplicity hypothesis cannot be ruled out either (remember - about half of all stars are found in multiple systems, so at least one in three of observed stars are probably multiple. No companion has been located on the sky, but a barely resolvable component remains possible.
All this positional work gives revised, and larger, uncertainties on the star's proper motions (in Right Ascension and in Declination), which project back to how closely the star's path would have intersected with the Sun's position. 5 of their 27 position estimates had to be discarded due to inconsistencies in the resultant dataset - which isn't terrible, but doesn't reduce the final uncertainty in the data. Putting it all together, they get a nominal closest approach between HD 7977 and the Sun to be equal 0.011 pc (∼2,300 au) during its passage 2.47 Myr ago, but with uncertainties on all factors (±0.024 pc in distance and ±0.03 Myr (30,000 yr, about 3 times the transit period of the star through the Oort cloud).
The issues identified here were also applied to the rest of the GAIA set of stars which appeared to have approached within a parsec of the Sun, identifying another two possible encounters. One of these, "P0533" (in the Stellar Potential Perturbers Database - "StePPeD") was quite close (0.223 pc) at 3.19 Myr ago, but weighs only an estimated 0.87 M☉. But the other new discovery (or identification really - it too was catalogued in the 1920s) "P3509" approached to (nominally) 0.402 pc at 3.94 Myr ago, but is estimated to weigh 3.50 M☉. That is much more likely to have had a noticeable effect.
Having established several new potential close-approaches, and some factors to consider in searching for more, the authors then move on to consider the effects of such a close encounter. Far and away most likely is that the star will pass close to a long-period comet, particularly at it's aphelion when it is moving most slowly and so is exposed to the passing star's gravity for the longest period of time. This could lead to ejection from the Soalr system (which we then wouldn't see) or it could deflect the comet to a closer aphelion). To further reduce the dataset, they only considered comets observed with a good orbit (well, obviously) and those with perihelion outside 3.5 AU (keeping them away from interactions with most of the asteroid belt and inner planets, but not avoiding Jupiter). Their interpretation is that close stellar approaches do increase, appreciably (maybe 40%, for the HD7977 close approach, alone). Several of their detailed study comets show major changes in orbital parameters due to interactions with these stars. But to me, the important point is that they're seeing multiple interactions within the period of one orbit - up to 4 or 5 times in one orbit. So, these interactions become the matter of noise in the record, not a cataclysmic single event. And we know form the geological record that - while major impacts do happen, life as a whole can handle them. It's a deal, but not a big deal.
Do these close encounters affect the planet's orbits?
The most likely planet to be affected is Neptune. It's furthes from the Sun, furthest from Jupiter, and (potentially) closest to the perturbing body. And, yes, it can be disrupted, but not very often. And we already know that it hasn't been. So ... what's going on? Is there an error in the analysis, or in interpretation of positional data (and hence closest approaches, resulting from unidentified multiple stars. And that reminds me that we're still not sure that the Sun is a single star.
I've got a headache now. The issues in astrometry are quite clearly explained. The results of the close aproaches are much harder to interpret. But we know - from the geological record - that bad things don't happen often enough to be important. Time for a break.
Totally by coincidence, I'm watching Anthony Hopkins eating people's faces as "Hannibal Lecter". Was the posing of a skinned+gutted cop with Red/White/Blue bunting in a "blood eagle" some way of prodding at American sensibilities? Are they really so sensitive about .. those three colours? The colours of who-knows how many flags around the world? In the words of Marvin (The Paranoid Philosopher Android ; the "clearest thinker I ever knew" (DentArthurDent), "It gives me a headache to think down to that level."
Truely a great comedy - for how it exposes people's irrationality.
So, I'm getting a bit ... ticked off with clicking the "open in new window" option on Blogger's "add link" dialog. So ... I should be able to put ' target="_blank" ' into the CSS style header for my "a" link. No? Need to check on a different page!
OK, well I tried that - at least simplistically with 'a {target:"_blank";}' in the "style" header block . Didn't work ; page opened in the same tag.
Now, why didn't it work?
Table fidding
Do I have unstructures ways to add a comment to a table. Or would a caption do? I've got "caption-side: bottom;" set in the style sheet.
I set up a TFOOT line below the TBODY section, including a TR with COLSPAN set to occupy the whole table.
I need to find a better way to set columns to R-align - better than cell-by-cell, at least. (Stack-Overflow suggests CSS of ... Which looks workable. But it's complicated. It's easier to change the default to , because that's what I'm going to use most often. And it's mucking up updating. Or is the system just broken? This is getting horribly complex - and not working.
One of the consequences of having something repeat is that you start to ask "how often does it repeat?". "is the rate changing", "is the rate not changing?", "is the rate noisy?", "is the rate not noisy?". As I used to say to my trainees, with a datum, you've got a datum ; with two data points, you've got a difference ; but with three data points, you can start to do meaningful sadistics." These authors agree. FTFAbstract :
In this work, we analyze the statistics of waiting time between bursts of three repeating FRBs from four data sets.
So, about the sparsest dataset you can hope to treat the numbers with sadistics and get something meaningful out. One of the most significant discoveries in the study of FRBs is the identification of a repeating FRB known as FRB 121102. Wait a minute - that has been repeatiung for a few years now. So how many events does it's sequence have? Quite a bit more data than the sparse set I just described. Sounds like a job for Wiki! Which gives me the 2012-11-02 first-identified burst, ten more identified from archived radio data in 2015. The next batch report was in December 2016 (one having been received on 13 November 2015, four on 19 November 2015, and one on 8 December 2015) - so that's giving a nice range of intervals already. On 26 August 2017, astronomers using data from the Green Bank Telescope detected 15 additional repeating FRBs coming from FRB 121102 More grist. Active little begger, this one! This also sounds like a well-planned observation campaign, because they wrung a lot more information from the data - polarization, and rotation of polarization. Hundreds more burst in 2018 through 2019, with a noticeable periodicity near 157 days. (This is coming back to me. The process of writing notes helps fix things in long-term memory. As any teacher could tell you.) So the data situation is by no means as dire as the introduction made out. Wiki isn't very good at separating the repeaters from the non-repeaters, and the data pile gets a bit confusing. Let's get back to the paper.
Since the identification of the first FRB in 2007, the tally of discovered FRBs has increased to over 700, with more than 60 shown repeating burst phenomena. Right, so the data situation is, indeed, far less serious than I'd inferred from the introduction. People are debating if all FRBs are repeating, but we don't happen to have the right telescope in the right mode and orientation at the right time. I'm sure some people are incorporating testing that into other observation programmes.
Working into the paper, the total data available is actually quite a lot :
FRB data
Source FRB
Burst (count)
Observed (hrs)
Observing run (d)
121102
1652
59.5
47
20201124A(A)
1863
82
54
20220912A
1076
8.67
55
20201124A(B)
881
~4
4
Totals
5472
154.17
160
Two distinct sequences of events at the location "20201124A" were recorded, designated here 'A' and 'B'. The event "20201124A" occurred on that date, at a location on the sky ; it repeated at other dates and times.
The relative abundance of data, spread across a range of locations, fluences (brightnesses) allows these scientists to pick out a scaling law where short intervals are followed by short intervals, and long intervals are followed by long intervals. This is decidedly different to the behaviour of a Poisson process - where the length of intervals is independent of previous behaviour.
This behaviour isn't unique to FRBs. Clustering of events following similar laws is also seen in earthquakes and solar flares (both events where there is a continuous accumulation of strain (mechanical, magnetic) leading to an event that reduces that strain. Which suggests models for what is happening in an FRB. Contrary to intuitive view, the probability of next burst occurring does not increase with the time t elapsed since the last burst; rather, it decreases and the expected residual time to the next burst ̂λ is also increased. […]Furthermore, the fluence of the subsequent burst does not increase with the waiting time but appears to be independent of it. Now that last part is really contra-intuitive. By no means unique (in thinking about earthquakes, a model of the fault "annealing" and getting stronger with time is often used. Of course, being buried in rock renowned for transparency, it is probably harder to see what is happening in an earthquake fracture zone than in something half-way across the universe (FRBs with high apparent redshift have been detected).
This work is one of the first I've seen (which doesn't say much) that uses a lot of data from the new Chinese Five-hundred-metre Aperture Spherical Telescope (FAST), to which I assume the authors are attached.
This is why I use Iarxiv : Regardless of the sequence that papers were submitted to Arχiv on the day in question, this one got filtered to the top of my pile by Iarxiv, on the basis that I'd followed links to other papers with similar keywords in the past - clearly a topic I'm interested in. Whatever their scoring algorithm, this one came in at a value of 0.65, when few papers make it above 0.4. If I continued to use the daily email (of all papers, in certain categories in Arχiv), then the papers would be ordered in sequence of submission (or acceptance - yes, Arχiv does do some refereeing of it's submissions). I may block most scripts on most sites, and block cross-site scripting to the likes of doubleclick and facebook, and auto-block a large list of advertising sites ; that's because I don't like advertisers distracting me, not because I don't understand what they're doing. If they do something of value to me, I might choose to accept their services. But if they don't provide anything of value to me, why should I provide them with information they can sell. But that's politics, not science. (Mentioning Iarxiv's use of "keywords", I guess I'd better add a few here.)
"Giant Impacts" were a bit of a shock when the concept was spreading in the 1970s. The appaling power of even regular impacts (Meteor/ Barringer Crater ; then Chicxulub - the "dinosaur killer") was disturbing to people who were getting somewhat used to the idea of thermonuclear annihilation (I grew up within cycling distance of a foreign nuclear base on "Aircraft Carrier 1". Imminent death for other people's gain changes your thinking.)
But the concept of a "Giant Impact" (the capitals seem appropriate) is inherent in the model of planet formation by growth of smaller bodies aggregating onto each other. "Aggregation" means either a relatively small body impacting a relatively large body (e.g. Chicxulub, regardless of it's effects of extinguishing ammonites, and some of the dinosaurs), or two nearly-equal size bodies impacting. Which latter is a "Giant Impact". And hence the interest in the "Giant" part of the impact range.
Worse - if you find the idea discomforting - is that most of the growth in size of planetesimals to become planets, comes from the mutual impact of similar-size bodies. If two bodies collide, one ten times the diameter of the other, then their ratio of masses is approximately 1000:1. So, to get the growth effect of a giant impact (with 50% mass loss) on the larger body, you need O(500) ("order of 500" of the smaller impacts? (Yes, the efficiency of accretion is an important factor. At least, if you're in the business of building planets.)
OK, enough general maundering. You can probably get much the same from Wiki (but see my caveat). Let's see what the "Annual Review of Earth and Planetary Sciences" has to say on the matter. This year.
First, RTFAbstract : their first substantive point is that the Giant Impact (hereafter, "GI") that formed the Moon is probably the one we have most information about. We have samples definitely from the resultant debris (a programme called Apollo, IIRC) ; we have more arguable samples from the target body (Earth has active geology ; it's accessible surface is almost certainly different to the surface - and depths - during the GI) ; we even know where the target body and debris are now, probably 4+ Gyr later (though they may have moved, significantly, in that time interval). Contenders for the second best known example might be the Pluto-Charon forming impact, or the (suggested) GI that gave Mars it's hemispheric dichotomy. (My caveat : the Wiki article is about specifically the "Moon"-forming impact, while it's title suggests it's more general application. Somewhere below I'll detail my compilation of data about which Solar system bodies have evidence suggesting a late-stage GI in their formation, but the total is that about 6 of the 11 largest bodies in the Solar system have GI-suggestive features.
Section 1 - Introduction
In the "Introduction" they introduce alternative terminology, and point at an interesting wrinkle : the common monikers are pairwise accretion and similar-sized collisions; aside from gas giants, there is little distinction between the terms similar size and similar mass. The wrinkle is that, because of internal compression, the mass of gas giants is complexly related to their mass. Contrary to intuition, as mass increases through Saturn size to Jupiter size, the radius increases, but somewhere not far above Jupiter mass, internal compression becomes more important and as the mass increases, the radius decreases. This continues (probably, by modelling) until about 80 Jupiter masses, when the core reaches the point of thermonuclear ignition. (What happens with temporary deuterium-powered fusion is an uncertain question.) That's an interesting wrinkle, but not really important to GI. The paper discussed above, about the impact of "sub-Neptunes" on each other is also very relevant in this - as you move from "rocky" planets ("planetesimals", "protoplanets", or even "small bodies") into the realm of "ice-giants" then "gas giants" the changing density profile through the bodies does result in changing impact behaviour.
Figure 1 : Pretty picture. For certain values of "pretty", probably best involving a very good telescope. Credit Andrew Gonzalez
The introduction mentions the important role of the (mutual) impact velocity (and hence kinetic energy and angular momentum) in analysing these particular impacts. And, as anyone who did ball-bearing on ball-bearing calculations at school (or played snooker after school), they're essential in rigid body collisions too. In planetary calculations, the velocities are generally normalised compared to the (mutual) escape velocity of the impacting bodies, vesc.
It is probably worth noting that most computational work in this area (all? possibly ; I can't remember hearing of another technique) is done with "smoothed particle hydrodynamics" (SPH) where the bodies are treated as collections of (relatively small) particles which have their own mass, volume, density, "stickiness", rigidity and gravity and they are thrown about in the computational arena until they either adhere to each other, or go beyond the computational limits of the modle. Mathematically simple (literally, you probably did this at school), but involving millions or billions of calculations per step of the model. Big number crunching like this used to need supercomputers ; modern recreational graphics hardware (GPUs) makes it a much cheaper task. I wonder if someone has tried to farm such work out to BOINC?
Giant impacts can result in many outcomes (see the "sub-Neptunes" paper discussed above), with impact factor (offset from a head-on collision) and collision velocity (comapred to vesc) as major determinants). The impacting bodies can merge almost fully (Venus, Uranus?), merge with debris (Earth-Moon, Pluto-Charon?), or be completely disrupted (myriads of asteroid belt examples?). Part of one body can be lost, and the other either lost or disrupted (Mercury, and it's missing mantle?). And the largest range of outcomes is classified as "hit and run", which results in some loss from both impactors, but both surviving (this is not much help when you're trying to build a larger planet).
Section 1 of the review discusses these ranges of outcomes, and the methematical underpinnings of the analyses. It's a review.
Section 2 - modelling
Section 2 discusses aspects of modelling. One thing that is reported that hasn't been much discussed previously is that if the impact velocity is higher than the speed of sound in the materials, thne the collision is supersonic, and understanding these events demands accurate shock equations of state - which is potentially amenable to laboratory investigation, involving big guns and exciting booms. Figure 4 puts this into context of impactor size and material - collisions involving Earth-size bodies are probably supersonic for forsterite (an olivine mineral, an approximation to mantle materials) but Mars or Mercury-size impactors are probably subsonic for forsterite, but supersonic for solid or liquid water. Asteroid belt size bodies, on the other hand are probably subsonic even for bodies rich in liquid water. That is news (to me).
This last is more relevant as collisions in the early Solar system are likely to have involved bodies that are relatively warm (compared to today) due to the presence (in the early Solar system ; this may not be a common situation) of short-lived radioisotopes such as 26Al from a recent nearby supernova. The isotopic signatures of this can be detected in Solar system specimens, but detecting such evidence remotely would be ... "challenging".
The presence of liquid water and the potential melting of solid water is important because it is relatively effective at converting impact energy to thermal energy. But it doesn't dispose of angular momentum. That makes the modelling of the impacts of particles in "SPH" further from inelastic "ball-bearings" and into the realm of soft, deformable bodies - needing a lot more computational grunt in your simulation. 20 years ago it was a problem that had to be ignored ; these decades, it's a problem that has to be faced - billion-fold.
Section 3 - Consequences
1- Well, duh, that's going to have consequences. Of course.
The contra-implication is that planets didn't form by myriads of "small" accretions. Which is something that you could reasonably argue for one, or a few, planets. But at some point it has to be faced for medium-size planet(-esimals). But, at some point, even if there were a mystical way of avoiding similar-size bodies from interacting, you'd end up with some "similar-size" bodies interacting. The issue can't be avoided.
Giant impacts in pebble accretion theory. Yes, certainly "pebbles" will interact, and accrete. The effects of within-particle cohesion and viscosity will lead to larger particles, eventually resulting in the similar-size interactions which are the subject.
Frankly, "pebble accretion" isn't a problem.
The unavoidably stochastic nature of "hierarchical growth" also, naturally, leads to a considerable diversity of outcomes from each collision, and each chain of collisions.
It may be disturbing to some that seemingly simple interactions following well-understood laws of physics can lead to uncertain outcomes. But that is the case. The word "seemingly" is important in that description.
Section 4 - Conclusions
Giant impacts are ubiquitous. As planetary systems evolve, the proportion of protoplanetary embryos (considered as approximately Moon-mass bodies, grown by pebble accretion or some other process, including smaller-scale GI) rapidly decreases until effectively no non-GI bodies are left. Bodies that are the products of a chain of ten, twenty or more GI are intrinsically possible. Reduction of numbers of planetary bodies is the only thing that stops this process.
In this context a "fractionally large moon" is one, like Earth's Moon, which is a significant fraction of the planet's size (3474.2 vs 12742 km diameter, 0.272 or 1/3.66 ratio ; 0.0202 oe 1/49 in volume).
THey start with an assertion I've always treated with considerable suspicion : that The Moon stabilizes the Earth’s spin axis at least by several degrees and contributes to Earth’s stable climate.Well, since Mars - without that "stabilisation" has obliquity (rotation axis to orbital plane angle) rate of change which can reach a degree per 10 kyr - which is should be within the capability of life to evolve (or migrate) around. As for how "necessary" it is ... well both Venus and Mercury are thought to be stabilised by interaction with the Sun. So how "necessary" is the Moon to life on Earth? (While checking my prejudices on this, I notice that significant Earth-obliquity: Moon resonances may occur in the next few Gyr, which also challenges just how important a "large Moon" is to life on Earth. (reference : Ward, W.R. (1982). "Comments on the Long-Term Stability of the Earth's Obliquity". Icarus. 50: 444 - 448 doi:10.1016/0019-1035(82)90134-8. ; It's open access, so go get it.)
Sorry, but I'm used to SF authors asserting that "The Moon is necessary for life to have evolved on Earth" or even that a "freakishly large Moon is essential to the development of life anywhere". Well, that may be good enough for an SF author, but I am far from convinced that it's a securely-founded opinion. Sorry - pet rant.
The gist of this work is that vapour rich planets involved in a giant impact (GI, see previous discussion) will produce a vapour-rich debris disk, within which many of the debris fragments from the collision will experience gas drag and re-accrete to the primary rather than forming a "fractionally large" satelite. To get a "fractionally large" satellite, you need a relatively large impact energy or low-Vapour Mass Fraction (VMF) impactors.
Which is well enough. There probably isn't enough information to say exactly what happened in the formation of the Solar system - but we do know that (1) it happened, and (2) models that can describe it happening are reasonably easy to construct.
Bloody hell, pushing 3 months since I touched this. Got to get back into this. 6 weeks visiting Dad didn't help, but I've got to get back into the habit.
So, what other things are in today's (well, yesterday's) list from Arχiv ?
Another MOND publication. An interesting topic, but primarily because the Internet Kook Department loves a conspiracy theory, and the (bullshit) "suppression of heterodox opinion" by the Illuminati, the Physics Orthodoxy, and Uncle Tom Cobbley is high on the list of popular idiocies. I've been tracking this for a while, mostly to piss-off the conspiracy wingnuts (TL;DR version - the field remains a moderate, but minor part of science publication). But in a random pick from Arχiv, there it is. [Distant sound of deflating Internet wind-bag. Or maybe not.]
Ultrashort Recurrence Time Nova M31N 2017-01e "Recurrent novae" are rare beasts. So it shouldn't be a great surprise to see that at least one has been spotted in the Andromeda Galaxy ("Messier 31", "M31" in the object's designation) because we can see most of the disc of that galaxy and half of the core, compared to under 1/3 of our galaxy. Which should remind me to check the status of the famous "T" variable in Corona Borealis ("T Cr B"), which has been observed to erupt twice, and which was predicted - with good clear reasoning - to erupt in May 2024 ± 6 months. Which prediction period we're getting to the end of. And it hasn't "gone" yet. Regarding the pattern-matching which constituted that "good, clear reasoning", it looks as if there is another cycle of the binary star's orbit to go before it goes "bang". That's the difficulty of making predictions, particularly regarding the future. It'll almost certainly go bang ; but when? That's the problem of dealing with small data sets - in this case a single recurrence after the original nova. What is this paper about? Prior to this report, the star had 4 known eruptions (discovery in 2017-01 ; a pre-covery in 2012-01, and subsequent observations in 2019-09 and 2022-03 ; see previous comment about datasets of 1) ; with an additional two eruptions the estimated timing has improved to 924 ± 7 days. Which is oddly consistent for a process that should have a significant random component to it. A 900-day recurrence time implies a very high accretion rate of material onto the (inferred) white dwarf. So, a potentially important system.
Narrowing down the Hubble tension to the first two rungs of distance ladders. OK, I'm not going to introduce the "Hubble Tension" here. But I bet @Dr_Becky covers this on her YouTube channel of "Night Sky News this week. Which reminds me of something else to do tonight. Long story short - because they had a large (and increasing) data set, they could divide the data into smaller groups where the derivation of distance had been done by different methods. And they found that the values of H0 derived with different distance estimate techniques show a discontinuity where there is a change from stage 2 (Cepheids-bearing host galaxies for SNe, z <e; 0.03) to stage 3 (using SNe as standard candles, 0.02 <e; z <e; 2.3) of the "cosmic distance ladder". Which suggests a systematic problem in one or other of stage 2 or 3. Which is pretty much what most people had been hoping to find, to resolve the "Hubble tension". The problem isn't solved - yet - but this is a pretty big step forward. What does Dr_Becky have to say? Well, she's back from holiday. Ah, bollocks - I forgot that youTube had started a new round of whack-a-mole against video downloaders. But since it's a Thursday paper, when she produces her videos, it hasn't made it into this week's NSN.
"Limits on planetary-mass primordial black holes from the OGLE high-cadence survey of the Magellanic Clouds" Pretty much does what it says on the tin. Almost any discussion of astrophysics or astronomy, even accompanying a well-based repoting set-up such as @Dr_Becky's (above) will almost inevitably have someone chiming in in the comments section, "What if Planet 9 were a black hole?" or "What if a runaway black hole were to come into the Solar system tomorrow?" While they're perfectly fair questions, the askers generally don't seem to know that we've been taking a census of such non-incandescent material in the Milky Way (and the part of it's halo towards the Magellanic Clouds), and (this is what upsets them) there's not a lot of it about. Not enough to solve Vera Rubin's early-1970s discovery of "flat" galactic rotation curves. Not enough to have a credible chance of ex-President Trump being head-shot by a primordial black hole. Such non-glowing conventional matter is present - but not in sufficient quantities to make long standing cosmological problems go away. Worse - we've known this since the first reports from such occultation programmes in the mid-1980s (I personally remember reading the reports in between lectures, over a cup of tea in the Student's Union.) They're a nice idea to solve various problems - but there are not enough of them about, and several whole (academic) generations of astronomers have known they're an insufficient solution to observational problems. Sorry, guys!
In-situ crystallographic mapping constrains sulfate deposition and timing in Jezero crater, Mars. That's a very geological one. Ca-sulphate minerals (they're careful to not say "gypsum" nor "anhydrite", so they plainly mean something else) have been reported from Mars for a while. Studying the crystallinity of these materials reveals some veins/ deposits were deposited more than 80m below then-current surface (so ... 80+m of erosion since then, to breing them to the present surface), while other veins were deposited much closer to the surface. Both types of rock sample are already cached for sample-return. Fun stuff, but it doesn't make Mars any the more habitable.
Anything from the oldest collection that I haven't thrown away yet? All the way back to June 30th.
An ancient Indian Solar eclipse recorded in myth. The Rig Veda (hindu holy book ; one of several) records an eclipse "vanquished" by Invisible Sky Fairies (&TM;). Based on "the eclipse [...] having occurred when the Vernal Equinox was in Orion, and three days prior to the Autumnal Equinox [... the authors] identify ‘Atri’s eclipse’ as the one that occurred on 22 October 4202 BC or on 19 October 3811 BC." There are considerable uncertainties when looking back this far (6000-odd years), not least of which is that the tidal friction of the Moon (well, the sub-lunar ocean bulge) starts adding up to thousands of seconds, or hours of Earth rotation, which is a substantial fraction of the sub-solar point's travel through the regions of Central Asia where the ancestors of the Hindu aristocracy were inhabiting in the time interval. The several centuries of time uncertainty also allow for up to 30°ree; of longitude variation between eclipses that would have been visible near the Iranian-Kazakh border (today), or sites as far east as the modern Afghan- Pakistan-China border.
What's this, Lassie? From the Aug 5 collection, "On Interstellar Quantum Communication and the Fermi Paradox"- sounds fun! Well, it does sound fun. Someone (the author) obviously thought "what sort of apparatus would be needed to transmit (and to receive) quantised data structures called "QuBits". Which, yes, fair enough question. Maybe the old stand-by of throwing "quantum" at a problem, like the Fermi Paradox ("where is everyone?") could result in a solution, sweetness, light and the odd Nobel gong for the lucky thinker. Tough luck : between Earth and Proxima Centauri, you'd need telescopes around 100km in diameter. Not going to happen soon ; may never happen. But worth feeding the guy while he scratches symbols on the blackboard.
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.
