RE: https://mastodon.social/@vicgrinberg/116177790478706357

Featuring #PrimordialBlackHoles near the end!

Curious gravitational wave may be hint at primordial black holes - or just noise

It’s a long shot, but scientists may have spotted exotic primordial black holes formed just after the Big Bang. Astronomers approach unusual observation with caution and excitement.

https://www.science.org/content/article/curious-gravitational-wave-may-be-hint-primordial-black-holes-or-just-noise

#Physics #GravitationalWaves #BlackHoles #PrimordialBlackHoles #science #news #astrophysics #astrodon #Cosmology

Weekly Update from the Open Journal of Astrophysics – 08/11/2025

It’s Saturday again, so it’s time for the usual update of the week’s new papers at the Open Journal of Astrophysics. Since the last update we have published another five papers, which brings the number in Volume 8 (2025) up to 168, and the total so far published by OJAp up to 403.

The first paper this week is “Maximizing Ariel’s Survey Leverage for Population-Level Studies of Exoplanets” by Nicolas B. Cowan and Ben Coull-Neveu (McGill University, Canada). This article was published in the folder Earth and Planetary Astrophysics on Tuesday 4th November 2025; it discusses various different schemes to select the mission reference sample for a notional three year transit spectroscopy survey with the European Space Agency’s Ariel mission

The overlay is here:

You can find the officially accepted version on arXiv here.

The Fediverse announcement is here:

Open Journal of Astrophysics

@[email protected]

New Publication at the Open Journal of Astrophysics: "Maximizing Ariel’s Survey Leverage for Population-Level Studies of Exoplanets" by Nicolas B. Cowan and Ben Coull-Neveu (McGill University, Canada)

https://doi.org/10.33232/001c.146656

The second paper of the week is “A substellar flyby that shaped the orbits of the giant planets” by Garett Brown (U. Toronto at Scarborough, Canada), Renu Malhotra (U. Arizona, USA) and Hanno Rein (U. Toronto at Scarborough, Canada). This article was published on Wednesday 5th November 2025, also in the folder Earth and Planetary Astrophysics. It argues that an ancient close encounter with a substellar object offers a plausible explanation for the origin of the moderate eccentricities and inclinations of the giant planets.

The overlay is here:

You can find the official version of this one on arXiv here. The federated announcement on Mastodon is here:

Open Journal of Astrophysics

@[email protected]

New Publication at the Open Journal of Astrophysics: "A substellar flyby that shaped the orbits of the giant planets" by Garett Brown (U. Toronto at Scarborough, Canada), Renu Malhotra (U. Arizona, USA) and Hanno Rein (U. Toronto at Scarborough, Canada)

https://doi.org/10.33232/001c.146688

Next one up is “The Potential Impact of Primordial Black Holes on Exoplanet Systems” by Garett Brown (U. Toronto at Scarborough), Linda He (Harvard U., USA),  and James Unwin (U. Illinois Chicago, USA). This one was also published on Wednesday 5th November 2025, but in the folder Astrophysics of Galaxies. This one is an exploration of the possibility that primordial black holes (PBHs) in our Galaxy, might impact the orbits of exoplanets. The overlay is here:

You can find the official accepted version on arXiv here. The fediverse announcement is here:

Open Journal of Astrophysics

@[email protected]

New Publication at the Open Journal of Astrophysics: "The Potential Impact of Primordial Black Holes on Exoplanet Systems" by Garett Brown (U. Toronto at Scarborough), Linda He (Harvard U., USA), James Unwin (U. Illinois Chicago, USA)

https://doi.org/10.33232/001c.146689

The fourth paper to report is “The Unhurried Universe: A Continued Search for Long Term Variability in ASAS-SN” by Sydney Petz, C. S. Kochanek & K. Z. Stanek (Ohio State U., USA), Benjamin J. Shappee (U. Hawaii, USA), Subo Dong (Peking University, China), J. L. Prieto (Universidad Diego Portales, Chile) and Todd A. Thompson (Ohio State U., USA). This one was also published on Wednesday November 5th 2025, but in the folder Solar and Stellar Astrophysics.  It describes the discovery and investigation of slowly-varying sources in the All Sky Automated Survey for SuperNovae (ASAS-AN) leading to the identification of 200 new variable stars. The overlay is here:

You can find the official published version on arXiv here. The Fediverse announcement follows:

Open Journal of Astrophysics

@[email protected]

New Publication at the Open Journal of Astrophysics: "The Unhurried Universe: A Continued Search for Long Term Variability in ASAS-SN" by Sydney Petz, C. S. Kochanek & K. Z. Stanek (Ohio State U., USA), Benjamin J. Shappee (U. Hawaii, USA), Subo Dong (Peking University, China), J. L. Prieto (Universidad Diego Portales, Chile) and Todd A. Thompson (Ohio State U., USA)

https://doi.org/10.33232/001c.146690

The fifth and final paper for this week is “Measuring the splashback feature: Dependence on halo properties and history” by Qiaorong S. Yu (Oxford U., UK) and 9 others based in the UK and USA. This was published on Friday 7th November 2025 in the folder Cosmology and Nongalactic Astrophysics. It discusses how the properties of “splashback” features in halo profiles relate to the halo’s assembly history (e.g. mass accretion rate and most recent merger time). The overlay is here:

The officially accepted version can be found on arXiv here. The Fediverse announcement is here:

Open Journal of Astrophysics

@[email protected]

New Publication at the Open Journal of Astrophysics: "Measuring the splashback feature: Dependence on halo properties and history" by Qiaorong S. Yu (Oxford U., UK) and 9 others based in the UK and USA.

https://doi.org/10.33232/001c.146824

That’s all the papers for this week. I’ll do another report next Saturday.

#Ariel #arXiv241204583v2 #arXiv250606429v2 #arXiv250705389v3 #arXiv250707174v2 #arXiv250722102v2 #CosmologyAndNonGalacticAstrophysics #DarkMatterHaloes #DiamondOpenAccess #DiamondOpenAccessPublishing #EarthAndPlanetaryAstrophysics #eccentricity #EuropeanSpaceAgency #exoplanets #ExtrrasolarPlanets #galaxyFormation #galaxyHaloes #GiantPlanets #OpenAccess #OpenJournalOfAstrophysics #primordialBlackHoles #Splashback #TheOpenJournalOfAstrophysics

A Primordial Black Hole?

There’s a recent paper on arXiv with the title A direct black hole mass measurement in a Little Red Dot at the Epoch of Reionizationon by Juodžbalis et al. that is causing a lot of interest. The paper is here and the abstract is:

There is a discussion of this in the Grauniad here and in several other places on the interwebs. It comes hard on the heels of the theoretical paper announced here.

I only saw this paper yesterday and, now that I’ve read it, it isn’t really all that clear to me what this object is. No doubt there’ll be considerable follow-up. One possibility – and it is just a possibility – is that we are seeing evidence of a primordial black hole, called a PBH for short. These are black holes formed by direct collapse in the early Universe rather than by merging of stellar black holes. Note the use of the word “naked” is rather misleading. It does not mean a naked singularity, in the sense of a singularity without an event horizon around it. In this case it just means that it appears not to be surrounded by accreting material or even a host galaxy.

A PBH of mass M would form at a particular cosmic time t if a region of radiius ~ct (the cosmological horizon scale) collapses into a black hole. Obviously this would require a large fluctuation in density on that scale but if a PBH does form then its mass will be roughly the mass contained within the horizon, i.e. M ~ ρ(t) (ct)3 (ignoring dimensionless factors). The sort of mass required (~106 M☉) corresponds to a time when the Universe was radiation-dominated and before matter and radiation decoupled. What would be inside such a black hole is therefore predominantly trapped radiation, which is Quite Interesting, but as far as the outside universe is considered it’s just a massive black hole.

Anyway, during radiation domination, the mass-energy density of the Universe ρ(t) ∝ t-2, so the horizon mass increases linearly with t. According to the standard cosmology, the epoch of radiation domination lasts for approximately 50,000 years after the Big Bang, i.e. of order 1012 seconds, and at the end of it the horizon mass is of order 1014 M☉. Assuming that the universe is completely radiation-dominated before that the time at which a PBH of mass 106 M☉ would form is about 104 seconds, i.e. getting on for 3 hours after the Big Bang. This is after the end of cosmological nucleosynthesis, but not by much. Primordial black holes of lower mass than this would form earlier, with a stellar mass PBH having to collapse around the time of the quark-hadron transition. Lighter PBHs would form even earlier.

The numbers I’ve quoted are very approximate, back-of-the-envelope, ballpark guesstimates. For one thing not all of the horizon mass will end up in a PBH: energy may well be released during the collapse. Moreover, some PBHs on one scale will subsequently be subsumed within objects of larger mass. Also I’ve ignored quite a lot of numerical factors. All this will have to be worked out properly, but there are potential constraints on any physical processes that might give rise to PBHs on the relevant scale if they involve a release of significant amount of energy as there may not be time for this excess to be thermalized by scattering or they may intefere with the element abundances predicted by nucleosynthesis.

That is all assuming it is a primordial black hole in the first place…

#arXiv250821748 #Cosmology #galaxyFormation #matterRadiationEquivalence #PBHs #primordialBlackHoles

Weekly Update from the Open Journal of Astrophysics – 30/08/2025

Once again it’s time for a summary of the week’s new papers at the Open Journal of Astrophysics. Since the last update we have published three new papers, which brings the number in Volume 8 (2025) up to 125, and the total so far published by OJAp up to 360.

The first paper to report this week is “Large-scale surveys of the quasar proximity effect” by Rupert Croft, Patrick Shaw & Ann-Marsha Alexis (Carnegie Mellon University; CMU), Nianyi Chen (Princeton), Yihao Zhou & Tiziana Di Matteo (CMU), Simeon Bird (UC Riverside), Patrick Lachance (CMU), and Yueying Ni (Harvard). This paper was published on Monday 25th August in the folder Cosmology and NonGalactic Astrophysics. It presents a CDM-based halo model of the quasar proximity effect, tested on quasar Lyman-alpha spectra from the ASTRID cosmological simulation, including self-consistent formation of quasar black holes and the intergalactic medium.

The overlay is here:

You can make this larger by clicking on it, as you can with all the overlays below. The officially accepted version of this paper can be found on the arXiv here.

The second paper this week, also published on Monday 25th August, but in the folder Astrophysics of Galaxies, is “Redshift evolution of Lyman continuum escape fraction after JWST” by Andrea Ferrara (Pisa), M. Giavalisco (UMass Amherst), L. Pentericci (Rome), E. Vanzella (Bologna), A. Calabrò (Rome) and M. Llerena (Rome). This paper is about the Attenuation-Free Model (AFM) for galaxies, in which radiation-driven outflows develop once the galaxy specific star formation rate exceeds a certain level, which is tested on data with positive results. The overlay is here:

You can find the officially accepted version on arXiv here.

The third and final paper this week is “Primordial black holes in cosmological simulations: growth prospects for supermassive black holes” by Lewis R Prole, John A Regan, Daxal Mehta & Peter Coles (National University of Ireland, Maynooth) and Pratika Dayal (Groningen, NL). This one was published in Astrophysics of Galaxies folder on Thursday 28th August 2025. You can read more about this paper here: basically it studies the growth of primordial black holes in the early Universe using numerical simulations, with implications for the subsequent formation of massive black holes.

The overlay is here:

You can find the officially accepted version of this one on arXiv here.

And that’s all the papers for this week. It’s still a bit slow as we emerge from the summer vacations, but I expect things will start to pick up from now on.

#arXiv250403848v2 #arXiv250510619v2 #arXiv250611233v2 #AstrophysicsOfGalaxies #AttenuationFreeModel #CosmologyAndNonGalacticAstrophysics #DiamondOpenAccess #DiamondOpenAccessPublishing #JWST #LymanContinuum #massiveBlackHoles #OpenJournalOfAstrophysics #primordialBlackHoles #ProximityEffect #quasars #TheOpenJournalOfAstrophysics