2023-03-01
2023-03 March readings
Well, trying to get back into the habits. I've got some hangovers from December to February, but cna I fight down the backlog?
| Planetary Science - Results of a new asteroid surface survey. |
| Cosmology - early galaxies |
| Cosmology - even earlier galaxies |
| Cosmology - A nearby dark galaxy. |
| Planetary Science - Jupiter’s interior and core |
| Planetary Science - Habitability of planets around white dwarfs. |
| Cosmology - The very first stars. |
| Planetary Science - A nearby exoplanet at 22pc |
| Cosmology - Does the speed of light vary through space. |
| Cosmology - The Radio to GeV Afterglow of GRB 221009A |
| End of document |
2023 March science readings.
"NEOROCKS project: surface properties of small near-Earth asteroids"
https://arxiv.org/pdf/2302.01165.pdfThis paper reports new initial spectroscopic analysis of 42 asteroid surfaces. The main result for space enthusiasts is that there is not one "M" class asteroid (metal-rich) surface in the collection.
The imagery that (many) people grow up with from Hollywood and TV "science" "documentaries" is that the Solar system is full of asteroids which are made of metal ready for mining to produce solid ingots of precious metals, with which the metals markets of Earth are likely to be crashed. That's Hollywood (perhaps somewhat influenced by a number of PR companies indulging in metals market manipulation), not reality. This result is about what you'd expect from the proportion of metallic asteroids - about 0.5%.
Some other pointers : Nearly 40% of the observed NEOs (16 out of 42) are classified as PHAs.
PHAs are Potentially Hazardous Asteroids. It's not terribly surprising - all asteroid surveys are going to be biased towards the bright ones - which means those that get relatively close to Earth (well … until we have significant observatory capability at (say) Earth-Sun L2 and L3). It sounds a frightening statistic, but it's not something that's going to keep me awake at night.
The asteroid mining fraternity dream of taking apart an M-type asteroid like Psyche, which is a fair enough dream. But they are relatively rare asteroids. A realistic "ISRU" (In-Situ Resource Utilisation) plans is going to have to expect to digest around 200 silicate mineral (and clay ("phyllosilicate"), and ice) asteroids for every metallic one they digest.
I suppose I should mention that 9 of the 42 bodies fall into the broader "X" classification, which can contain "M" class asteroids with less distinctive spectroscopic results - such as asteroids with only a small amount of metal on the surface. Given the size of the set considered in this work, up to one quarter of one of the bodies observed might be metallic. Which is still not terribly good news for the asteroid miners. In reality, almost all asteroid mining is going to find (and need to use) is silicates, and probably a fair amount of "ices" which could feed a "plastics" processsing plant. If you have inherited a vision from SF of massive foundries smelting whole asteroids into "hull metal", best leave that image in Hollywood.
The NEORocks program's home page is here. One of their main aims is to focus on extremely high standards in data dissemination
.
Regular Rotation and low Turbulence in a diverse sample of z~4.5 galaxies observed with ALMA
https://arxiv.org/pdf/2302.03049.pdfThe context is that we have models of how galaxies developed from primordial gas clouds (with or without the first generation of stars contaminating the gas clouds with (astrophysical) "metals") ... but as we're improving our IR and radio astronomy (JWST, ALMA ...) , those models are not agreeing with reality. Which Feynman had a blunt response to. This is a moderate part of that "tension" - the observed galaxies have better developed discs, reduced turbulence and more ordered structures than were expected. Not a huge amount earlier, but eyebrow raising. Another paper in the pile (next section, here) discusses observations at z ~8 which are much more challenging for the star formation and galaxy formation models.
This is a "moderate" tension result. But what grabbed me is that I tested my "Redshift Calculator" on it and got an "Age of Universe" figure for z~4.5 of 1.3 Gyr - the paper says "more than 1.5Gyr ago", which I take as "agreement", since they've got a sample of five galaxies. The corresponding age figure for observations at z~8 is 0.6 Gyr - which puts a lot more stress on the question of "how to build a galaxy, fast?"
I note that the rotation curves produced for the galaxies in this set show (figure 6) the "flat" profile of velocities rather than a simple Keplerian drop-off. As Vera Rubin deduced in the 1970s (and Fritz Zwicky saw hints at in the late 1930s), this implies that the visible galaxy is embedded in a considerably bigger, but less concentrated, disc of gravitating matter - the original "dark matter" observation.
A massive interacting galaxy 525 million years after the Big Bang
https://arxiv.org/pdf/2303.00306.pdfWell, if the previous section discussed a … tension in astrophysics, of the form "it is awkward for our models of galaxy development to produce a well-structured galaxy in less than 1.5 Gyr", then how much more inconvenient to find evidence of a "massive interacting …" (see paper title)? That's a much worse tension. Almost any revision of models that accommodates this observation is going to make the previous section pretty much "mainstream". Which is the significance of the paper.
Abstract (highlights)
JWST observations confirmed the existence of galaxies as early as 300 million years and with a higher number density than what was expected based on galaxy formation models and Hubble Space Telescope observations.
New data, old models were wrong. Film at 11.
a high-resolution spectroscopic and spatially resolved study of a rare bright galaxy at a redshift z = 9.3127 ± 0.0002 (525 million years after the Big Bang) with an estimated stellar mass of (2.5 +0.7 −0.5) × 109 Msol
Thats broadly the mass of the Milky way. And again, my redshift-to-distance-time converter is in agrement. Worth the effort invested.
The star formation rate, however is considerably higher than for the Milky Way. Which makes sense for a "young" galaxy. Similarly for the metallicity - about a tenth of that locally. Also sensible. So, the modelling tension is in the big-scale end of galaxy formation, rather than at the small end of star formation and evolution.
The system has a morphology typically associated to two interacting galaxies, with a two-component main clump of very young stars (age less than 10 million years) surrounded by an extended stellar population (130 ± 20 million years old […]) and an elongated clumpy tidal tail.
Uhhh ... well the universe was smaller then (that's what redshift means, after all) So, interactions would be expected. Tidal tails, we see "today", so that's not breaking any hearts.
Our observations provide evidence of rapid and efficient built up of mass and metals in the immediate aftermath of the Big Bang through mergers, demonstrating that massive galaxies with several billion stars are present at earlier times than expected.
My Discussion
The big contribution of JWST to previous (Hubble, Spitzer) observations this far back, is that JWST can do sufficient spectroscopy to identify "metals", and their approximate quantities. "suggesting that [we] are missing key physical processes connected to the formation of first galaxies
". No doubt the popular science press will present this as "astronomers baffled" by "revolutionary data" ; the actual position and reaction is a bit less dramatic.
The remaining 50-odd pages of the paper are the technical details of how the observations were turned into astronomical parameters. I'm not qualified to comment on those details, but that's what the "peer" in "peer review" stands for.
Discovery of an isolated dark dwarf galaxy in the nearby universe
https://arxiv.org/pdf/2302.02646.pdfThis is the first substantive discovery I've seen reported from the Chinese "Five-hundred-meter Aperture Spherical radio Telescope" (FAST) - whose comissioning phase started (approximately) at the same time as the damage (then collapse) of the "thousand foot" (300-odd m) radio telescope at Arecibo, Puerto Rico after ... I've forgotten the name of the hurricane. But it was a hurricane that did it, possibly exacerbated by some botched US government responses.
The radio telescope detected a patch of hydrogen gas emission with a pattern of frequency variation consistent with it being a rotating mass (some areas rotating towards us, some rotating away). Checking against optical images of the region, the area didn't have a large amount of starlight (less than 100,000 Sun-like stars worth) while the rotation data suggested a mass of hydrogen about a thousand time larger. The redshift for the body is 0.0083, suggesting a distance of about 36.8 Mpc (Planck best-estimate cosmology ; 120 million light years).
As noted in the previous two readings, the understanding of how physics gets from the Cosmic Microwave Background to building galaxies is not well understood. We have models, but they're clearly not in good agreement with reality, so the models need to be changed. That's more in the range of changing a few parameters in a large equation than substituting four elephants on the back of a cosmic turtle as a model of the universe. But someone is going to take it as meaning that.
Someone is going to object to 120 million light years away being described as "nearby". But I'm OK with that because if they had an arbitrarily good telescope, they'd be able to see Terrestrial mammals - that's recent!
"Jupiter’s interior from Juno: Equation-of-state uncertainties and dilute core extent"
https://arxiv.org/pdf/2302.09082.pdfThe second biggest event in the formation of the Solar system (after the Sun starting to fuse hydrogen in it's core) was the formation of the core of Jupiter, rapidly followed by it accumulating most of it's mass from the gas-rich disc of material surrounding the (heating up) sun. This must have happened quite quickly, because what we see around modern very young stars is that the "lighting up" of the central star rapidly drives away the remaining parts of the molecular cloud from which it grew.
The orbit of the probe "Juno" was designed to investigate this question. While basic Newtonian theory says that a spherical mass has a very simple gravitational field, if we model Jupiter as a core of an Earth-like density surrounded by a shell of gaseous (if compressed) hydrogen, we'd get a slightly different gravitational field, particularly when the spacecraft is relatively close to the core. Which means, flying from a long way from the planet to as close as possible to the "cloud tops". The spacecraft will accelerate slightly differently in this "dive" if the core is large compared to if it is small (or non-existent). Which is part of the reason for Juno's trajectory to have been designed as long loops away from the planet, with much shorter high speed "dives" past the cloud tops. Intermediate parts of the flight path make close approaches to the various satellites.
So, how big is Jupiter's core, and how sure are we about that?
Frankly, we still don't know. Past work has suggested a core of around 20% of Jupiters mass, with possibly a diffuse upper margin. This work doesn't contradict that, but also can't confirm it, because our knowledge of the "Equation of State" (EoS, relating pressure and density) for a mixture of hydrogen, helium and some "metals" (beryllium upwards on the periodic table) isn't well enough known to confidently get an internal model from the experimental data. So, it's time to dig out the diamond anvil presses, line up the heating and measuring lasers, and get back to trying to measure those EoSs to try to wring more data from the spacecraft's observed motions.
That's the Carnegie Geophysics lab (with nearly a century of experience in such experiments ; other Geophysical labs are available), doing space science on machines designed to probe the interior of the Earth. There's something I like about that. Unfortunately, it's not a storywith a clear conclusion. Yet.
The Influence of Tidal Heating on the Habitability of Planets Orbiting White Dwarfs
ArXiv 2303.02217Abstract
[..]we revisit the prospects for habitability around these post-main-sequence star systems. In addition to the typically considered radiative input luminosity, potentially habitable planets around white dwarfs are also subjected to significant tidal heating. The combination of these two heating sources can, for a narrow range of planetary properties and orbital parameters, continuously maintain surface temperatures amenable for habitability for planets around white dwarfs over time scales up to 10 Gyr.
That's not exactly surprising - since the first discovery of extra-solar planets (around a pulsar!) people have wondered what could happen on them. The cooling history of the white dwarfs (and pulsars) is extended, so if you can have planets form there, you might have a geological history and potentially a biological history. Adding a second, also long-lived, heat source to the planets could make that a more long-lasting situation too. Certainly worth invvestigating.
What sort of planets could survive their parent star going red giant - or even supernova? For "rocky" planets outside the actual radius of the red giant, that's not a major problem - even Earth is anticipated to survive the Sun's RG phase, unles it is actually enveloped (which is a "definite maybe". Whether the gas giants (Jupiter in particular) survive the Sun's RG phase ... and with how much mass, is an open question. One of the "plusar planets" mentioned above is thought to be a gas giant core which has been stripped of it's atmosphere leaving a carbon-rich core which might be mostly the diamond allotrope of carbon.
The presence of an outer "gas giant" (or it's core) would potentially enhance the production of tidal interactions and heating. That's my 0.10€ worth.
With regard to "pulsar planets" there's another constraint - to form a pulsar needs a fairly large star, which means a short lifetime. Estimates for the time to form a Jupiter are Order(10Myr), so any star of more than about 12.5 solar masses would go through it's catastrophic final development phases while it's planets are still forming. That's very challenging - particularly for a gas giant. Not only does the planet need to survive the heat flux from the supernova, but it is still radiating it's "heat of accretion". Very challenging for a planet to survive a supernova. Less challenging for a planet to form after a supernova in an accretion disc around a pulsar.
Time to RTFP, to see if the authors worked on it too.
Observations have demonstrated that an estimated 25 – 50% of white dwarfs have spectroscopic evidence for pollution that implies accretion of planetary material.
Well, that's a surprise to me. If that is anything like correct, then it means that the distribution of planets around WDs is pretty similar to that around stars in general. Or, equivalently, the RG phase of stellar evolution is not terribly destructive to the existence of planets in orbit around the star
The basic problem of habitability of planets around white dwarfs is written in the "cooling curves" for white dwarfs of different sizes. That's an almost pure physics problem - a "spherical cow" cooling in a vacuum, where the cow really is spherical. The calculated habitability zone decreases from around 1AU at 10 Myr afteer the origin of the white dwarf, to about 0.01AU 10Gyr after white dwarf formation. That's not considering tidal heating.
Tidal heating requires non-zero orbital eccentricity or non-synchronous rotation to operate.
Well, yes. On the other hand, most orbiting bodies do have non-zero eccentricity, and maintaining synchronous rotation through the orbital changes needed to stay in a "habitable zone" is going to be challenging too. It's probably safe to say that most white dwarf planets would need tidal heating to be considered in their budgets, even if it's only a minor effect. The authors also consider that for a planet to migrate from outside the area cleared by the red giant phase into the area of potential habitability, they're most likely to have done that by tidal migration, which requires significant eccentricity.
Drawing on work from the 1960s, 70s and 90s, the authors then develop some expressions for estimating the surface temperatures of planets, when including tidal heating. The addition of tidal heating can extend the duration of "habitability" by a factor of up to 10 for more moderate degrees of orbital evolution of the planet. Over a wider range of planetary parameters the duration of habitability can be increased from 1-3 Gyr to 6 to 10Gyr - which is the predicted duration of habitability on Earth. While the specifics of the calculation depend on the physical properties of the planet, we have demonstrated that tidal heating may play a critical role in the habitability of planets around white dwarfs.
Caveats
No account is taken of the atmospheric properties of the planet. It's sure to have an effect, but generally that would be to broaden the habitable zone rather than narrow it.
It is unlikely that these planets would exist in isolation. The spectroscopy shows that "planetary" material is being accreted onto the surface of the white dwarfs, so there must be a regular flow. That means, unavoidably, impacts on the planets under consideration. Whether that's a big deal or not ... nobody knows. Earth probably survived a "late heavy bombardment" during the period that life first developed (though the peak intensity and duration are in considerable doubt).
Discussion
This is a quite interesting finding telling us that we can't exclude white dwarfs from consideration as potential places to search for biosignatures (or even, "ET"). Which is OK.
The most massive Population III stars
https://arxiv.org/pdf/2302.09763.pdf" ; really early stars, possibly visible with JWST ; when did they form, and what does that reveal?
Background : several generations ago (1926 to 1944), astronomers messed up. They noticed that some areas of galaxies had relatively blue stars and called them "Population I" (letter "capital i", not digit "one"), while more yellowish stars dominated the cores of galaxies and globular clusters, and were called "Population II" stars. That was a purely descriptive category - they could as well have been called "John", "Paul", "George" or "Ringo" - but it turned out to be age-related, with Population I stars having a higher "metallicity" than Population II stars (when spectroscopy improved through the 1950s and 60s, to measure the metal content of stars with sufficient accuracy. ("Metal" in the astrophysical sense of "any atom that isn't hydrogen or helium".) Unfortunately, the chosen labels were opposite to the direction of growth, and nobody bit the bullet of changing the terminology. So when a (then-hypothetical) class of really early stars, with extremely low (almost zero) class of stars was proposed in the late 1970s, they were called "Population III", and the terminology misfit was cemented in place. So, "Population III" stars are some of the first stars that formed in the universe. Some (low mass) ones are probably stil present today (spectroscopic surveys are in work to identify them, nearby ; to be 12+ Gyr old, they must have a mass lower than about 0.96 the mass of the Sun, so luminosity less than 0.8 that of the Sun), but this paper is about the other end of the mass spectrum.
Those high-mass stars had short lives, and contaminated the "primordial" material of the universe with it's first doses of "metals", which changed the absorbtion properties of that material so they can't easily form really big stars. But those "really big stars" also have really big deaths - supernovae, or "hyper novae" which produced (it is thought) gamma ray bursts (GRBs), maybe groups of interacting neutron stars and black holes which themselves produce gravitational wave events from their mergers, and a whole plethora of other interesting events.
Which is the context behind the paper.
As a side effect, these extreme-mass Population III stars probably seeded the super-massive black holes (SMBHs) at the centres of galaxies. SMBHs as a side-effect - that's some serious shade being thrown.
The actual paper is a development of a new method for estimating the efficiency of early-universe star formation, out of which masses of plausible Population III stars emerge failry naturally (well the authors say so, and got it past peer review ; the maths are beyond me). At red shifts of 10~20 (so dates of 180~470 Myr after the big bang) there should be Order(1,000~10,000) of these hypermassive Population III stars visible to the JWST. Which is justification enough to plan an observing programme. Whether it gets observing time in competition with the other calls on the observatory's time.
An Earth-sized Planet around an M5 Dwarf Star at 22 pc
https://arxiv.org/pdf/2302.00699.pdf22pc (parsecs) is pretty close ; our closest star (other than the Sun) is Proxima Centauri at 1.3pc (4.24ly) away. An "M5 dwarf" is one of the commonest types of star in the Milky Way galaxy, and this report ... well the title of the paper says most of what needs to be said.
Obviously, being close-by (22pc, 71.7ly) this straight-off goes high in the schedules of telescope time to confirm (or deny) the existence of the planet, to try to find more planets, and to seek spectroscopic evidence of it's atmospheric composition (if it has an atmosphere.
With a stellar mass of about 0.16 of the Sun's mass, this system has the potential to exist for a long time. About a thousand billion years (compared to the Sun's current 4.5 billion year (Gyr) age and the universe's age of 13.27 Gyr. The planet's mass isn't well-constrained (yet - telescope time will be being booked) at 3.0±2.7 Earth masses it's not a planet with an analogue in the Solar system, but these "super-Earth" or "sub-Neptune" planets are a common find in other planetary systems. (The mass is fairly uncertain, so the plausible composition could be anything from almost pure iron to a rock-ice mixture.) That lack of an analogue is going to be a challenge to planetary scientists to interpret it's atmospheric characteristics, which in turn will greatly affect the degree of global warming the planet undergoes and therefore it's surface (and atmospheric) temperatures. The planets "year" of 4.01 days is short by our standards, but not remarkably short by the cohort of characterised exoplanets. The estimated surface temperatures (ignoring any global arming atmospheric effects is in the range 377~412 K (104~139°C) but could be within the liquid water range if the albedo (reflectivity) was high, such as a heavily clouded planet. That will give SF writers somewhere to re-settle all their stories originally set in a 1950s "Jungles of Venus" environment.
It's a nice planet, and potentially encouraging for exploration. At 22pc, it may be within reach of technologies like the "Breakthrough Starshot" programme. Since that programme would construct considerable propulsion equipment on Earth, then once the first "swarm" of fly-by projectiles is en route to it's target, there would be 20-plus years between the end of the launch programme and the first arrivals at Proxima Centauri. It would not be rational to leave those assets to rust in those intervening decades.
Do current cosmological observations hint at the speed of light variability?
https://arxiv.org/pdf/2302.00867.pdfVarying speed of light is a popular straw for the Star Trek wannabees and the God-squad to clutch at. The bad news from this, which used the most recent data is, no significant evidence for speed of light variability (but some statistically insignificant evidence in the more distant measures, where the noise is highest.
There is a common trope that "scientists don't think outside the box". This is the sort of report that gives the lie to that claim. Scientists do look at paradigm-breaking ideas like "c can vary with time or space". But they typically find that the paradigm-breaking version of the idea doesn't actually conform with the evidence. And as everyone's favourite Nobel laureate says, "if it disagrees with experiment, it [your beautiful idea] is wrong."
Another popular "paradigm breaking" idea is that Newton's gravitational concept is significantly wrong (we know already that it's wrong in detail - that's Einstein's General Relativity ; but that collapses back to Newtonian results at low speeds, masses and fields). If it's such a "suppressed" (another common accusation) subject, how come a search of ArXiv paper abstracts for "MOND" (MOdified Newtonian Dynamics - probably the best developed alternative to Newtonian-Einstinian gravitational theory) yeilds 16 papers on the subject since the start of 2023 (as I write in mid-March). That's hardly "supression".
The Radio to GeV Afterglow of GRB 221009A
https://arxiv.org/pdf/2302.04388.pdfThis paper is probably too esoteric for Slashdot itself, but I'd not noticed GRB221009A previously. It's a helluva beast. [Wiki]
- lasted for more than ten hours since detection,
- could briefly be observed by amateur astronomers.
- This is also one of the closest gamma-ray bursts and is among the most energetic and luminous bursts.
Redshift is given as z= 0.151 … which my calculator (something is broken on that page) gives as 1.95 Gyr look-back time, and 644.3 Mpc (2101.1 Mly) which is close enough to the Wikipedia values (they're probably using a different spacetime model to me. See the redshift discussion linked to above.
Anyway, it's a beast, and I missed it. Only 5 months ago, so the flush of results should be turning up now.
Slashdot submission
Necessary, because the editors frequently muck about with the submission, contrary to the general opinion that they do nothing.
A recent paper on ArXiv describes a Gamma Ray Burst (GRB) whose light arrived late last year as one of the strongest ever observed. GRB 221009A was detected on October 9 last year (yes, that number is a date), so 5 and a bit months from event to papers published is remarkably quick, and I anticipate that there will be a lot more papers on it in the future.
Stand-out points are :
- - it lasted for more than ten hours after detection (a space x-ray telescope had time to orbit out of the Earth's shadow and observe it)
- - it could (briefly) be observed by amateur astronomers.
- - it is also one of the closest gamma-ray bursts seen and is among the most energetic and luminous bursts.
It's redshift is given as z= 0.151, which Wikipedia translates as occurring 1.9 billion years ago, at a distance of 2.4 billion light-years from Earth.
Observations have been made of the burst in radio telescopes (many sites, continuing), optical (1 site ; analysis of HST imaging is still in work), ultraviolet (1 space telescope), x-ray (2 space telescopes) and gamma ray (1 sapce telescope) - over a range of 1,000,000,000,000,000-fold (10^15) in wavelength. It's brightness is such that radio observatories are expected to continue to detect it for "years to come".
The model of the source is of several (3~10) Earth-masses of material ejected from (whatever, probably a compact body (neutron star or black dwarf) merger) and impacting the interstellar medium at relativistic speeds (Lorentz factor >sim;9, velocity >99.2% of c). The absolute brightness of the burst is high (about 10^43 J) and it is made to seem brighter by being close, and also by the energy being emitted in a narrow jet ("beamed"), which we happen to be near the axis of.
General news sites are starting to notice the reports, including the hilarious acronym of "BOAT - Brightest Of All Time". Obviously, with observations having only occurred for about 50 years. we're likely to see something else as bright within the next 50 years.
The brightness of the x-rays from this GRB is such that the x-rays scattered from dust in our galaxy creates halos around the source - which are bright enough to see, and to tell us things about the dust in our galaxy (which is generally very hard to see). Those images are more photogenic than the normal imagery for GRBs - which is nothing - so you'll see them a lot.
This got posted to the front page by "EditorDavid" on 2023-04-01 21:34 (Sat April 1st, oops - I should have anticipated that ; "oh dear, what a pity, never mind"), so it's probably a good time to close this page out and start April's page.
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Labels: Arxiv, Science, Slashdot
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