Further to my earlier post, I refer you to this much more detailed article by someone actually involved in the LIGO experiment, former Cardiff colleague Bernard Schutz..
Archive for the The Universe and Stuff Category
More on the 10th Anniversary of Gravitational Waves
Posted in The Universe and Stuff with tags Advanced LIGO, Bernard Schutz, Black hole merger, gravitational waves, GW Astronomy, GW150914 on September 14, 2025 by telescoperA Decade of Gravitational Waves
Posted in Biographical, The Universe and Stuff with tags Advanced LIGO, arXiv:2508.18082, Black hole merger, black holes, gravitational waves, GW150914, inspiral on September 14, 2025 by telescoperThis is just a quick post to mark the fact that it is now ten years to the day since the first detection of gravitational waves by Advanced LIGO. The acronym LIGO stands for Laser Interferometer Gravitational-wave Observatory, by the way. It wasn’t until February 11th 2016 that the result was announced at a press conference (which I blogged about here), but the signal itself arrived on 14th September 2015, exactly a decade ago; the name given to the event was GW150914.
Here are the plots for that first one:
That first signal corresponded to the coalescence of two black holes, of masses 29 and 36 times the mass of the Sun and produced a large response in the detectors very soon after Advanced LIGO was switched on. There’s synchronicity for you! The LIGO collaboration have done wondrous things getting their sensitivity down to such a level that they can measure such a tiny effect, but there still has to be an event producing a signal to measure. Collisions of two such massive black holes are probably extremely rare so it’s a bit of good fortune that one happened just at the right time. Actually it was during an engineering test.
There have been many subsequent detections and even more candidates waiting to be confirmed- here’s a full list. The official LIGO site states there are 90 confirmed detections, the 4th observational run (O4) (which is due to end in November 2025) has already found 200 candidates. The latest compilation of gravitational-wave transient sources can be found here.
Most of the detections have been binary black hole mergers, but I particularly remember the excitement in 2017 surrounding the first merger of a neutron star with a black hole. It was fun that rumours started to spread via this blog as people outside the LIGO/transient source community used a comments thread here to share information of what various telescopes were looking at. That was in August 2017, just over 8 years ago.
Anyway, here’s to the next decade. Assuming NSF does not follow Trump’s plan to slash the LIGO budget.
Weekly Update from the Open Journal of Astrophysics – 13/09/2025
Posted in OJAp Papers, Open Access, The Universe and Stuff with tags arXiv:2309.03270v3, arXiv:2407.08718v2, arXiv:2504.06174v3, arXiv:2505.13145v2, arXiv:2506.13716v2, arXiv:2507.11801v2, arXiv:2507.21268v2, Atacama Large Aperture Submillimeter Telescope, AtLAST, Correlation Functions, Cosmology and NonGalactic Astrophysics, Diamond Open Access, Focused Transport Equation, galaxy clusters, Instrumentation and Methods for Astrophysics, Microwave Spectroscopy, Open Journal of Astrophysics, Protoplanetary Disk, protoplanetary disks, Solar and Stellar Astrophysics, solar observations, Spin-2 fields, Statistical methods, strong gravitational lensing, Superluminous Supernovae, SWIFT, The Open Journal of Astrophysics, weak gravitational lensing on September 13, 2025 by telescoperIt’s Saturday again, so it’s time for another summary of the week’s new papers at the Open Journal of Astrophysics. Since the last update we have published seven new papers, which brings the number in Volume 8 (2025) up to 134, and the total so far published by OJAp up to 369. We seem to be emerging for the slight late-summer hiatus we have experienced over the last few weeks.
Anyway, the first paper to report this week is “Observing the Sun with the Atacama Large Aperture Submillimeter Telescope (AtLAST): Forecasting Full-disk Observations” by Mats Kirkaune & Sven Wedemeyer (U. Oslo, Norway), Joshiwa van Marrewijk (Leiden U., Netherlands), Tony Mroczkowski (ESO, Garching, Germany) and Thomas W. Morris (Yale, USA). This paper discusses possible strategies and parameters for full-disk observations of the Sun using the proposed Atacama Large Aperture Submillimeter Telescope (AtLAST). It was published on Tuesday 9th September 2025 in the folder Solar and Stellar Astrophysics.
The overlay is here:
You can make this larger by clicking on it. The officially accepted version of this paper can be found on the arXiv here.
The second paper this week, published on Wednesday 10th September in the folder Cosmology and NonGalactic Astrophysics, is “The exact non-Gaussian weak lensing likelihood: A framework to calculate analytic likelihoods for correlation functions on masked Gaussian random fields” by Veronika Oehl and Tilman Tröster (ETH Zurich, Switzerland). This paper shows how to calculate likelihoods for the correlation functions of spin-2 Gaussian random fields defined on the sphere in the presence of a mask with applications to weak gravitational lensing.
The overlay is here:
and you can find the final accepted version on arXiv here.
Next one up, the third paper this week, is “Subspace Approximation to the Focused Transport Equation. II. The Modified Form” by B. Klippenstein and Andreas Shalchi (U. Manitoba, Canada). This was also published on 10th September 2025 in the folder Solar and Stellar Astrophysics. It is about solving the focused transport equation analytically and numerically using the subspace method in two or more dimensions.
You can find the final accepted version on arXiv here.
The fourth paper of this week was also published on Wednesday 10th September. It is “Mass models of galaxy clusters from a non-parametric weak-lensing reconstruction” by Tobias Mistele (Case Western Reserve U., USA), Federico Lelli (INAF, Firenze, Italy), Stacy McGaugh (Case Western), James Schombert (U. Oregon, USA) and Benoit Famaey (Université de Strasbourg, France). Published in the folder Cosmology and NonGalactic Astrophysics, it presents new, non-parametric deprojection method for weak gravitational lensing applied to a sample of galaxy clusters. The overlay is here:
You can find the officially accepted version on arXiv here.
The fifth paper of the week is “A Swift Fix II: Physical Parameters of Type I Superluminous Supernovae” by Jason T. Hinkle & Benjamin J. Shappee (U. Hawaii, USA) and Michael A. Tucke (Ohio State, USA). This one was published on Thursday 11th September 2025 in the folder High-Energy Astrophysical Phenomena. The paper uses recalibrated Swift photometry to recompute peak luminosities and other properties of a sample of superluminous Type I supernovae. The overlay is here:
You can find the official accepted version on arXiv here.
Paper No. 6 for this week is “Detailed Microwave Continuum Spectra from Bright Protoplanetary Disks in Taurus” by Caleb Painter (Harvard, USA) and 11 others, too numerous to mention by name, based in the USA, Germany, Mexico and Taiwan. This one was published in the folder marked Solar and Stellar Astrophysics on September 11th 2025. It presents new observations sampling the microwave (4-360 GHz) continuum spectra from eight young stellar systems in the Taurus region. The overlay is here:
The final version can be found on arXiv here.
The last paper for this update is “On Soft Clustering For Correlation Estimators” by Edward Berman (Northeastern University, USA) and 13 others based in the USA, France, Denmark and Finland and Cosmos-Web:The JWST Cosmic Origins Survey. This was published on Friday 12th September 2025 in the folder Instrumentation and Methods for Astrophysics. It presents an algorithm for estimating correlations that clusters objects in a probabilistic fashion, enabling the uncertainty caused by clustering to be quantified simply through model inference. The overlay is here:
You can find the final version on arXiv here.
And that’s all the papers for this week. I’ve noticed a significant recent increase in the number of papers in Solar and Stellar Astrophysics, which means we’re broadening our impact across the community. Which is nice.
P.S. I found out last week that, according to NASA/ADS, papers in OJAp have now accumulated over 5000 citations.
Einstein’s First Lecture in Britain
Posted in Biographical, History, The Universe and Stuff with tags Albert Einstein, University of Manchester on September 12, 2025 by telescoperTidying a few things up ahead of the start of term I discovered this old clipping, yellowed with age, and decided to scan it before it disintegrates entirely:
It is from the (then) Manchester Guardian which is now known as the Grauniad. The article is dated 1st October 1921, which implies that the talk must have been on the afternoon of Friday 30th September 1921. However, the University of Manchester website states that the talk was on June 9th 1921. During his visit, Einstein was awarded an Honorary Doctorate of Science by the University of Manchester, which is recorded here as having been presented on June 8th, so it appears the Guardian piece was published some time after the event. As usual, Einstein gave his lecture – to a packed house – entirely in German, as he did when he lectured in Nottingham almost a decade later.
Einstein was already famous by 1921 – largely thanks to the 1919 Eclipse results (see, e.g., here) – but it was still before he won his Nobel Prize (in 1922).
Anyway, the text down the right-hand side of the Guardian piece can be found here; it’s well worth reading!
Weekly Update from the Open Journal of Astrophysics – 06/09/2025
Posted in OJAp Papers, Open Access, The Universe and Stuff with tags arXiv:2411.17682v2, arXiv:2509.01545v1, Be Star, Black Hole Binary, Cosmology and NonGalactic Astrophysics, Diamond Open Access, Diamond Open Access Publishing, Dispersion Measures, fast radio bursts, Open Journal of Astrophysics, Solar and Stellar Astrophysics, The Open Journal of Astrophysics on September 6, 2025 by telescoperIt’s Saturday again, so 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 two new papers, which brings the number in Volume 8 (2025) up to 127, and the total so far published by OJAp up to 362. It’s been another relatively slow week, not least because of the Labor (sic) Day holiday in the USA on Monday which, among other things, meant there was no arXiv update on Tuesday.
Anyway, the first paper to report this week is “An analytical model for the dispersion measure of Fast Radio Burst host galaxies” by Robert Reischke, Michael Kovač & Andrina Nicola (U. Bonn, Germany), Steffen Hagstotz (Ludwig-Maximilians Universität München) and Aurel Schneider (U. Zurich, Switzlerland). This is a theoretical study of the dispersion measures (DMs) intrinsic to host galaxies of Fast Radio Burst (FRB) sources to enable separation of that from the line-of-sight DM. This one was published on Monday 1st September 2025 in the folder Cosmology and NonGalactic Astrophysics.
The overlay is here:
You can make this larger by clicking on it. The officially accepted version of this paper can be found on the arXiv here.
The second paper this week, published on Wednesday 3rd Sepember in the folder Solar and Stellar Astrophysics, is “Complex spectral variability and hints of a luminous companion in the Be star + black hole binary candidate ALS 8814” by Kareem El-Badry (Caltech, USA), Matthias Fabry (Villanova U., USA), Hugues Sana (KU Leuven, Belgium), Tomer Shenar (Tel Aviv U., Israel) and Rhys Seeburger (MPA Heidelberg, Germany).
The overlay for this one is here:
You can find the officially accepted version 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, we have a lot of papers in the pipeline that I expect to emerge pretty soon.
A Hitchhiker’s Guide to the Swampland
Posted in Maynooth, The Universe and Stuff with tags arXiv:2509.02632, Cosmology, Kay Lehnert, Maynooth University, Swampland, swampland conjectures on September 5, 2025 by telescoperA very comprehensive review article has appeared on arXiv with the title Hitchhiker’s Guide to the Swampland: The Cosmologist’s Handbook to the string-theoretical Swampland Programme by Kay Lehnert (who just happens to be my PhD student). The paper is 170 pages long and contains over 1,800 references, which gives some idea of what a large field this is and how much work Kay has put into writing it!
The abstract reads
String theory has strong implications for cosmology: it tells us that we cannot have a cosmological constant, that single-field slow-roll inflation is ruled out, and that black holes decay. We elucidate the origin of these statements within the string-theoretical swampland programme. The swampland programme is generating a growing body of insights that have yet to be incorporated into cosmological models. Taking a cosmologist’s perspective, we highlight the relevance of swampland conjectures to black holes, dark matter, dark energy, and inflation, including their implications for scalar fields such as quintessence and axions. Our goal is to inspire cosmological model builders to examine the compatibility of effective field theories with quantum gravitational UV completions and to address outstanding cosmological tensions such as the Hubble tension. This comprehensive literature review presents clear definitions, cosmological implications, and the current status – including evidence and counterexamples – of the following swampland conjectures: the anti-de Sitter distance conjecture (AdSDC), the completeness conjecture (CC), the cobordism conjecture, the de Sitter conjecture (dSC), the swampland distance conjecture (SDC), the emergence proposal (EP), the Festina Lente Bound (FLB), the finite number of massless fields conjecture (or finite flux vacua conjecture (FFV)), the no global symmetries conjecture, the no non-supersymmetric theories conjecture, the non-negative null energy condition conjecture, the positive Gauss-Bonnet term conjecture, the species scale conjecture, the gravitino swampland conjecture (GSC), the tadpole conjecture, the tameness conjecture, the trans-Planckian censorship conjecture (tPCC/TCC), the unique geodesic conjecture, and the weak gravity conjecture (WGC), including the repulsive force conjecture (RFC).
This is essentially the literature review part of Kay’s thesis; the aim of his research is to study the implications of the string-theoretical swampland programme for cosmology. He’s particularly interested in the predictions string theory makes regarding inflation, dark energy, and dark matter, and the impact this has on the Hubble tension. The point of writing this review was to suggest projects that might be undertaken to bring string theory into the realm of testability, thus suppling material for the rest of Kay’s thesis, but I think it is also a very good guide for cosmologists of all types to what the swampland conjectures are and what they do and do not say about the Universe we actually live in.
A Primordial Black Hole?
Posted in The Universe and Stuff with tags arXiv:2508.21748, Cosmology, galaxy formation, matter-radiation equivalence, PBHs, primordial black holes on September 3, 2025 by telescoperThere’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…
Galaxies and Black Holes in the First Billion Years
Posted in Biographical, The Universe and Stuff with tags arXiv:2508.16948, black holes, Cosmology, galaxy formation, JWST, Richard Ellis on September 1, 2025 by telescoperTrying to catch up on recent developments in galaxy formation? I can heartily recommend an excellent review article on the subject by Richard Ellis which you can find on the arXiv here. The abstract reads:
I present written notes from three lectures given at the 54th Saas-Fee Advanced Course of the Swiss Society of Astrophysics and Astronomy in January 2025 entitled “Galaxies and Black Holes in the First Billion Years as seen by the JWST”. I focused my lectures on progress in studies of cosmic reionisation, the properties of galaxies in the reionisation era, topics related to the redshift frontier and the search for Population III stars. The lectures were given to graduate students in astrophysics and cover both pedagogical material as well as observational results from the first two and half years of JWST science operations. The pace of discovery with JWST is, of course, rapid and so my lectures discuss long-term goals, analysis methods and their assumptions and limitations in the hope that the underlying material will retain value in the near future. In this written version, the visual material is that presented at Saas-Fee in January 2025 but I have provided updates on progress from the literature up to August 2025. The material is aimed at early career researchers and should not be considered as a scholarly review of the entire JWST literature on high redshift galaxies.
It’s quite a long article (65 pages) but nicely written and well worth reading, as it is full of information about recent advances as well as historical insights. Talking of which, there’s a picture on page 41 taken at a meeting in Durham in 1988 called The Epoch of Galaxy Formation that I attended while I was still a graduate student:
Richard Ellis himself is in the front row, left of centre with light-coloured trousers, checked shirt and hands in pockets. I’m in the picture too, but I’ll leave it up to you to find me!
A poll was held among the delegates at that meeting about various questions to do with galaxy formation. The majority opinions revealed by these votes nearly all turned out to be utterly wrong! That’s progress, I guess…
Weekly Update from the Open Journal of Astrophysics – 30/08/2025
Posted in OJAp Papers, Open Access, The Universe and Stuff with tags arXiv:2504.03848v2, arXiv:2505.10619v2, arXiv:2506.11233v2, Astrophysics of Galaxies, Attenuation Free Model, Cosmology and NonGalactic Astrophysics, Diamond Open Access, Diamond Open Access Publishing, JWST, Lyman Continuum, massive black holes, Open Journal of Astrophysics, primordial black holes, Proximity effect, quasars, The Open Journal of Astrophysics on August 30, 2025 by telescoperOnce 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.
Primordial Black Holes in Cosmological Simulations – Update
Posted in Maynooth, The Universe and Stuff with tags arXiv:2506.11233, black holes, primordial black holes on August 28, 2025 by telescoperJust time for a quick update about a paper that I posted about at the start of the summer, when it appeared on arXiv. At that time it had already gained a bit of traction in the media, e.g. here. Well, the paper is now published in the Open Journal of Astrophysics. Obviously, as an author I was conflicted so not involved in the editorial process.
Here is the overlay:
For those of you not in the field, there is currently a big mystery about how galaxies we have found at high redshift with JWST managed to acquire massive black holes so early in the Universe’s evolution. Black holes can grow quickly in a dense environment by accreting mass onto an initial seed, but what are the seeds? In this paper we investigate the possibility that they were primordial black holes. These form directly from fluctuations in the early Universe, as opposed to astrophysical black holes which form from stellar collapse. We don’t know exactly what mass primordial black holes would have nor how numerous they would be, but this paper uses high-resolution numerical experiments to investigate their effects if they do exist.
Here’s a pretty picture which is a zoom into 200 pc of the full simulation. I think 10pc counts as high resolution for a cosmological simulation! The blue circle shows the most massive PBH in the simulation, the green circle shows its nearest neighbour. The colour scale represents the number-density of dark matter particles.
For more details, read the paper!
In the Dark 