Dark Star

[Recusant]

After a site search, and specifically the Science board, it seems that the term dark star is practically absent here. The term itself has been around since at least the 1800s though I imagine it was probably used in astrology or in a metaphorical sense at that time. In pop culture, off the top of my head I note that it's the title of a somewhat bleak science fiction film, and a Grateful Dead song. I haven't heard it in science before that I can recall.

This item could go in the cosmology thread, but right now it seems more like a specific bit of science exotica. I don't know how recently scientists started speculating about a star at least partially composed of dark matter, but it's something I hadn't considered. Dr. Ilie, quoted in the article, appears to be pretty certain they exist.

"JWST May Have The Best Evidence Yet of a Bizarre 'Dark Star'" | Science Alert

JWST might have spotted the 'smoking gun' of a hypothetical object called a dark star in the distant Universe. If confirmed, this discovery could solve several mysteries of physics.

A dark star may sound like an oxymoron, but it would still emit light and energy. It wouldn't be powered by nuclear fusion like a garden-variety star, however – it would be running on a core of interacting dark matter particles.

"Supermassive dark stars are extremely bright, giant, yet puffy clouds made primarily out of hydrogen and helium, which are supported against gravitational collapse by the minute amounts of self-annihilating dark matter inside them," says Cosmin Ilie, an astrophysicist at Colgate University in the US.

Now, researchers have found the best evidence so far for the existence of dark stars. While studying four of the most distant objects ever observed, the team found that all are consistent with a dark star explanation.

Most intriguingly, though, one of the objects showed a particular light absorption feature at the wavelength of 1,640 Angstrom. This is considered a sure sign of dark stars, which arises from singly ionized helium in their atmospheres.

"While the signal-to-noise ratio of this feature is relatively low, it is the first time we found a potential smoking gun signature of a dark star. Which, in itself, is remarkable," says Ilie [University of Texas press release].

Soon after JWST fired up in 2021 and began peering farther back in space and time than humans ever had before, it caught some unexpected sights. Near the dawn of time sat what looked like huge galaxies at a moment when there shouldn't have been enough time (literally) for them to have grown so big.

Astrophysicists quickly came up with a possible explanation for some of these: Dark stars, which could contain as much as a million Suns-worth of mass, would look similar to galaxies from this distance.

[Continues . . .]

The paper is open access:

"Spectroscopic Supermassive Dark Star candidates" | Proceedings of the National Academy of Sciences

Abstract:

Dark Stars (DSs), i.e., early stars composed almost entirely of hydrogen and helium but powered by Dark Matter (DM), could form in zero metallicity clouds located close to the center of high redshift DM halos. In 2023, three of us identified (in a PNAS work) the first three photometric DS candidates: JADES-GS-z11-0, JADES-GS-z12-0, and JADES-GS-z13-0.

We report here our results of a follow-up analysis based on available NIRSpec JWST data. We find that JADES-GS-z11-0 and JADES-GS-z13-0 are spectroscopically consistent with a DS interpretation. Moreover, we find two additional spectroscopic DS candidates: JADES-GS-z14-0 and JADES-GS-z14-1, with the former being the second most distant luminous object ever observed.

We furthermore identify, in the spectrum of JADES-GS-z14-0, a tentative feature (S/N ~ 2) indicative of the smoking gun signature of DSs: the He II 1640 absorption line. In view of ALMA's recent identification of a probable O III nebular emission line in the spectrum of JADES-GS-z14-0, the simple interpretation of this object as an isolated DS is unlikely.

If both spectral features survive follow-up observations, it would imply a DS embedded in a metal rich environment, requiring theoretical refinements of the formation of evolution of DSs, which in previous studies were assumed to form in isolation, without any companions.

[Dark Lightning]

That's wild stuff!

[The Magic Pudding..]

I like the CSNY Darkstar, it used to be on the end of 45/90 minute tape.
If an album didn't fill up a side a good song from a weak album often got added.

[Recusant]

Yeah that's a fine track. A well-played Rhodes piano is something I always enjoy. 

 


This seems as good a dark matter thread as any for this item.

"Mysterious Glow Detected in Space Could Be Dark Matter Destroying Itself" | Science Alert

A strange gamma-ray glow emanating from the heart of the Milky Way could be the long-sought fingerprint of dark matter particles annihilating each other, evidence suggests.

A new research effort involving simulations of Milky-Way-like galaxies shows that the mysterious, unexplained extra gamma radiation emanating from the region is equally likely to be due to dark matter annihilation as to millisecond pulsars – and the dark matter hypothesis might even have a slight edge.

"Dark matter dominates the Universe and holds galaxies together. It's extremely consequential and we're desperately thinking all the time of ideas as to how we could detect it," says astrophysicist Joseph Silk of Johns Hopkins University.

"Gamma rays, and specifically the excess light we're observing at the center of our galaxy, could be our first clue."

This gamma-ray glow, known as the Galactic Center GeV Excess (GCE), has puzzled astronomers since its discovery in 2009 in data from NASA's Fermi Gamma-ray Space Telescope. Something in the galactic center is producing a glow in the highest-energy form of light in the Universe, but whatever that something is, astronomers have yet to pin it down.

There are two leading candidates. One of those is dark matter, the mysterious source of extra gravity hanging around the Universe that can't be explained by the normal matter that makes up everything we can directly detect.

[. . .]

The other candidate is millisecond pulsars. These are neutron stars at the very end of their life cycle, formed from the collapsed core of a massive star that has ejected most of its material in a supernova explosion. What makes a neutron star a pulsar is its extremely rapid spin. As it spins, it emits beams of radio waves, particles, and radiation, including X-rays and gamma rays. As these beams sweep around, the pulsar appears to, well, pulse.

Astronomers have yet to detect the population of pulsars that could be responsible for the GCE, but there are ways to narrow down the possibilities. The population of old stars that should include pulsars in the galactic bulge – the central, bubble-shaped region of the Milky Way – seems to form an X-shape, while previous research suggests the Milky Way's dark matter halo is spherical.

[Continues . . .]

The paper is behind a paywall, but I found a preprint version:

"Fermi-LAT Galactic Center Excess morphology of dark matter in simulations of the Milky Way galaxy" | arXiv

Abstract (as published):

The strongest experimental evidence for dark matter is the Galactic Center gamma-ray excess observed by the Fermi telescope and even predicted prior to discovery as a potential dark matter signature via weakly interacting massive particle dark matter self-annihilations. However, an equally compelling explanation of the excess gamma-ray flux refers to a population of old millisecond pulsars that also accounts for the observed boxy morphology inferred from the bulge old star population.

We employ a set of Milky Way-like galaxies found in the hestia constrained simulations of the local universe to explore the rich morphology of the central dark matter distribution, motivated by the GAIA discovery of a vigorous early merging history of the Milky Way galaxy. We predict a significantly nonspherical gamma-ray morphology from the weakly interacting massive particle interpretation. Future experiments, such as the Cherenkov Telescope Array, that extend to higher energies, should distinguish between the competing interpretations.

[Recusant]

I've been enjoying the abundance of items having to do with dark matter and its nature, not to mention places where it could be. In this instance, an exploration of the possibility that Sagittarius A* (Sgr A*) the supermassive black hole at the center of our galaxy, is actually a dense region of dark matter. Speculate away! I find it gratifying that people are willing to explore ideas about the Universe by looking at the same. This in contrast to the supposed divinely bestowed knowledge contained in collections of old books of mythology.

Just for a larf, indulging my curiosity I checked in with the Christians to find what they have to say about dark matter. You have to be in the right mood but if you are, there are some amusing items. I admit I can be a sucker for desperate tap-dancing. 


"Something Far Darker Than a Black Hole Could Hide in The Heart of The Milky Way" | ScienceAlert

There's no denying that something massive lurks at the heart of the Milky Way galaxy, but a new study asks whether a supermassive black hole is the only possible explanation.

All measurements taken of the galactic center to date are consistent with a highly dense object around 4 million times as massive as the Sun. According to the new paper, though, if you squint just a little, all that evidence can also apply to a giant, compact blob of fermionic dark matter, without an event horizon.

We currently don't have the observational precision to tell the difference between these two models. However, a dark matter composition of the galactic nucleus would give astronomers a new tool for interpreting the dark matter structure of the entire galaxy.

"We are not just replacing the black hole with a dark object; we are proposing that the supermassive central object and the galaxy's dark matter halo are two manifestations of the same, continuous substance," explains astrophysicist Carlos Argüelles of the Institute of Astrophysics La Plata in Argentina.

[Continues . . .]

The paper is open access:

"The dynamics of S-stars and G-sources orbiting a supermassive compact object made of fermionic dark matter" | Monthly Notices of the Royal Astronomical Society

Abstract:

Surrounding Sgr A*, a cluster of young and massive stars coexist with a population of dust-enshrouded objects, whose astrometric data can be used to scrutinize the nature of Sgr A*. An alternative to the black hole (BH) scenario has been recently proposed in terms of a supermassive compact object composed of self-gravitating fermionic dark matter (DM). Such horizon-less configurations can reproduce the relativistic effects measured for S2 orbit, while being part of a single continuous configuration whose extended halo reproduces the latest GAIA-DR3 rotation curve.

In this work, we statistically compare different fermionic DM configurations aimed to fit the astrometric data of S2, and five G-sources, and compare with the BH potential when appropriate. We sample the parameter spaces via Markov Chain Monte Carlo statistics and perform a quantitative comparison estimating Bayes factors for models that share the same likelihood function.

We extend previous results of the S2 and G2 orbital fits for 56 keV fermions (low core-compactness) and show the results for 300 keV fermions (high core-compactness). For the selected S2 data set, the former model is slightly favoured over the latter. However, more precise S2 data sets, as obtained by the GRAVITY instrument, remain to be analysed in light of the fermionic models.

For the G-objects, no conclusive preference emerges between models. For all stellar objects tested, the BH and fermionic models predict orbital parameters that differ by less than 1 per cent. More accurate data, particularly from stars closer to Sgr A*, is necessary to statistically distinguish between the models considered.

[Dark Lightning]

Astrophysics is one of those areas where a lot of latitude is still available. What I studied 45 years ago looks Copernican by comparison. 

[Recusant]

Agreed. The Universe has plenty of curiosities and more unveiled as we build more powerful instruments. Early days yet for the Webb telescope and it's already shown us some amazing things. The Hubble is still excellent too--was used to help create the image behind the observation described below. Noting the usual headline editor's tendency to overstate things, creating certainty out of possibility.                         



"Dark star" you say? Well how about a dark galaxy?

Deep, man.     

"Hubble and Euclid Team Up To Identify A Dark Matter Galaxy" | Universe Today

Everybody knows that galaxies are large structures made of stars. That's a simple definition, and ignores the fact that galaxies also contain gas, dust, planets, moons, comets, asteroids, etc., and of course, dark matter. But one type of galaxy is mostly made of dark matter, and they're difficult to detect.

They're called dark galaxies, and they contain no stars, or only very few stars. Scientists have long theorized about their existence, which has remained hypothetical; they've found galaxies with low surface brightness, and they've found dark galaxy candidates. But new research has found the strongest candidate yet.

[. . .]

The candidate galaxy has been dubbed CDG-2, for Candidate Dark Galaxy 2. (CDG-1 is explained here.) CDG-2 is in the Perseus galaxy cluster about 300 million light-years away. The obvious question is, if it's so dark how was it detected?

It comes down to globular clusters (GC). Most galaxies have GCs. They're spherical groups of stars that are bound together gravitationally and can contain millions of stars. Around spiral galaxies like ours, they're mostly found in the galactic halo. Their origins are unclear, as is the role they play in the evolution of galaxies.

In this work, the researchers used the Hubble, the ESA's Euclid space telescope, and Japan's Subaru telescope. They searched for tight groupings of GCs that could indicate the presence of a galaxy. The Hubble found four closely-connected GCs in the Perseus cluster. The researchers then applied advanced statistical methods on data from the three telescopes that revealed a faint glow around the GCs. This glow is a strong indication that there's an underlying galaxy whose individual stars are too dim to resolve.

"This is the first galaxy detected solely through its globular cluster population," lead author Li said in a press release. "Under conservative assumptions, the four clusters represent the entire globular cluster population of CDG-2."

[Continues . . .]

The paper is open access:

"Candidate Dark Galaxy-2: Validation and Analysis of an Almost Dark Galaxy in the Perseus Cluster" | The Astrophysical Journal Letters

Abstract:

Candidate Dark Galaxy-2 (CDG-2) is a potential dark galaxy consisting of four globular clusters (GCs) in the Perseus cluster, first identified in D. Li et al. through a sophisticated statistical method. The method searched for overdensities of GCs from a Hubble Space Telescope (HST) survey targeting Perseus.

Using the same HST images and new imaging data from the Euclid survey, we report the detection of extremely faint but significant diffuse emission around the four GCs of CDG-2. We thus have exceptionally strong evidence that CDG-2 is a galaxy.

This is the first galaxy detected purely through its GC population. Under the conservative assumption that the four GCs make up the entire GC population, preliminary analysis shows that CDG-2 has a total luminosity of L_V,gal = 6.2 ± 3.0 × 106 L⊙ and a minimum GC luminosity of L_V,GC = 1.03 ± 0.2 × 106 L⊙.

Our results indicate that CDG-2 is one of the faintest galaxies having associated GCs, while at least ∼16.6% of its light is contained in its GC population. This ratio is likely to be much higher (∼33%) if CDG-2 has a canonical GC luminosity function (GCLF). In addition, if the previously observed GC-to-halo mass relations apply to CDG-2, it would have a minimum dark matter halo mass fraction of 99.94% to 99.98%. If it has a canonical GCLF, then the dark matter halo mass fraction is ≳99.99%. Therefore, CDG-2 may be the most GC dominated galaxy and potentially one of the most dark matter dominated galaxies ever discovered.