It’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.
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 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!
This is Figure 3 from Kays paper. If you would like to know more of what it is about, turn to page 50…
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.
Yesterday the official Presidential Election Order was tabled which means that an election for the office of President of Ireland (Uachtarán na hÉireann) will be held in the Republic on Friday 24th October 2025. The incumbent Michael D. Higgins will have served his second 7-year term by November and since by the Constitution nobody can hold the office more than twice, we will have a new President of the Republic.
The Irish media have been trying to make news about the presidential election all summer, which has been pointless and tedious to put up as no candidates had even been nominated then. Actually nobody has yet either, as nominations don’t officially open until tomorrow; they close on September 25th. Still, at least the process has started.
In order to progress to the election, a candidate has to receive the support of at least 20 members of the Oireachtas or at least 4 local authorities (i.e. councils). Former or retiring Presidents can nominate themselves but this is not relevant here.
The way the election works is that voters rank all candidates. In the first round of counting, first preference votes are totted up and if one candidate has more than 50% he/she is elected. If not an Instant Runoff method is used, with votes of lower-ranked being reallocated until there’s a winner (ie until one candidate gains a majority).
I just checked the online electoral register to confirm my status:
I will wait to see who has acually been nominated before deciding who to vote for. In the last Presidential Election (2018), five candidates opposed the re-election of Michael D. Higgins, three of them businessmen best known for having appeared on the Irish version of the TV show Dragon’s Den. There’s ample evidence from elsewhere that the products of reality TV shows do not make good presidents. Neither do rapists, so let’s hope Conor McGregor does not get nominated. It is likely that there will be more than six candidates this time and the election will be more closely contested that last time. In 2018 the turnout was very low, no noubt because many people assumed – correctly – that Higgins would win. In the event he got over 56% of the first-preference vote so the transfers were irrelevant. That might not be the case this time.
The Presidency of Ireland is a ceremonial rather than an executive office, and it has little actual power associated with it. It is nevertheless important in that the President is the guardian of the Constitution as well as representing the Irish Nation as a kind of ambassador and as patron of many good causes. Surprisingly, some of the people who want to put themselves forward don’t seem to know anything about what the job entails. Hopefully, the more obvious fruitcakes who put themselves forward will fail to get nominated. I think Michael D. Higgns has carried out his duties in a very dignified and diligent way over the years, and will be a very hard act to follow. I’ve been proud to have him as my President.
It’s hard to believe that seven whole years have passed since the last election. There’s another reminder of that coming up on Friday September 12th when I will be going to the National Concert Hall for a performance by the National Symphony Orchestra that marks the opening of the 2025/6 season. On September 15th 2018 I went to the season opener for that year. That was also my first ever visit to the National Concert Hall. To mark the occasion we were in the presence of the man himself , Michael D Higgins, and his wife Sabena. The President attended as Patron of the National Symphony Orchestra. I don’t know whether he will attend on Friday 12th September, but if he does I’m sure he will get a good ovation. As well as many other things Michael D. Higgins has been a very strong advocate for the Arts in Ireland. I’m not sure his successor will live up to the standard he set.
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 Grauniadhere 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 (~106M☉) 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.
Graphic by European Space Agency showing how structure formation might be affected by PBH formation
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 1014M☉. Assuming that the universe is completely radiation-dominated before that the time at which a PBH of mass 106M☉ 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…
Your love and pity doth the impression fill Which vulgar scandal stamp’d upon my brow; For what care I who calls me well or ill, So you o’er-green my bad, my good allow? You are my all the world, and I must strive To know my shames and praises from your tongue; None else to me, nor I to none alive, That my steel’d sense or changes right or wrong. In so profound abysm I throw all care Of others’ voices, that my adder’s sense To critic and to flatterer stopped are. Mark how with my neglect I do dispense: You are so strongly in my purpose bred That all the world besides methinks are dead.
I find myself returning once again to Shakespeare’s sonnets, especially to the sequence of 126 poems that the poet addressed to a “Fair Youth“. This one is written in quite difficult language (for me) with some obscure words and phrases such as “adder’s sense”, “o’er-green” and “steel’d sense”. It’s almost as if parts of it are written in code. Nevertheless the overall meaning of the poem is clear: it revolves around the beautiful “You are my all the world” in line 5, shining out through the thickets, with “all the world” repeated in the last line for extra effect. The poet is saying that nobody’s opinion of him matters at all except that of his beloved. Know the feeling?
Trying 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…
I’ve been seeing the phrase vibe coding bandied about quite a lot these days and it always makes me think of Lionel Hampton. Since it’s now September and it’s raining outside, today it made me think of this recording of Lionel Hampton playing September in the Rain. How’s that for a link?
This track was recorded in Paris in 1953, an LP of which was released in 1956. I have a later issue of it. It features members of Hamp’s band, which was ona European tour at the time, alongside a number of local musicians. For a long time it puzzled me that among the musicians present was clarinettist Mezz Mezzrow whose style didn’t seem to fit. Eventually it was explained to me that Mezzy was the man who could be relied upon to supply appropriate smoking materials. This number however is chiefly Hamp on his own, on vibes (naturally), and frequently accompanying himself on vocals (sort of).
Close Up of Highlighting Specific Word Research in a Dictionary
While I remember, and before I get caught up in start-of-term things, I thought I would pass on news that two calls administered by Research Ireland will open on September 11th. These are the Government of Ireland Postgraduate Scholarships and the Government of Ireland Postdoctoral Fellowships. These are open to applications from candidates anywhere in the world.
You can find information about the Postgraduate Scholarships here and the Postdoctoral Fellowships here. The postdoctoral positions are for one or two years; postgraduate positions are for 2 years (Research Masters) or 4 years (PhD).
The application deadline is 23rd October 2025 and positions of both types are to start on 1st September 2026. You will need to contact possible supervisors at your planned host institute in advance of application so there isn’t much time.
Anyone interested in applying to hold one of these positions in Maynooth is welcome to contact me privately for advice or assistance. Given my rapidly approaching retirement, however, I am not able to act as nominated supervisor for postgraduate positions. I would happily support an applicant for a postdoctoral fellowship in the area of cosmology. There are of course many other potential supervisors both at Maynooth and elsewhere.
Today is the last day of August, which, according to my calculations, means that tomorrow is the first day of September. Last week the kids started to go back to school and some of course started for the first time. I think the schools vary in the timetable for new arrivals and returning students, but they’re basically all operating fully from tomorrow, Monday 1st September.
Universities start back a little later, though this also varies. In Maynooth, Orientation Week (for new students) begins on September 15th, and lectures commence for all years on September 22nd, which happens to be the day of the Autumnal Equinox. My first lecture of the new academic year is on that day. I don’t know how many students I’ll have in my class yet. It’s a 4th-year class, and those students don’t register for modules until Friday 12th September, at the end of a week that begins with new students starting to enrol on Monday 8th September.
The first week of September will therefore be a bit quieter in the University than in the local schools. Next week sees a number of conferring ceremonies at which students who completed their studies with the examinations in May will receive their degrees. That includes a number of Physics students, who will graduate on Wednesday 3rd September. Unfortunately, when I tried to register to attend the ceremony, a few weeks ago, I was unable to because it was booked up so I’ll have to send my congratulations virtually. In any case, Conferring ceremonies at Maynooth are not what they used to be. Instead of the atmospheric surroundings of the Aula Maxima, they are now held in the soulless environnment of a lecture theatre. Instead of a nice buffet reception afterwards the graduates used to get, they now get a cup of tea in a paper cup and (if they’re lucky) a very small Danish pastry. It’s quite embarrassing actually. I wouldn’t be surprised if, in future, graduands were told to being their own sandwiches and a thermos flask. Anyway, a PhD student of mine will attend a conferring ceremony at the end of October. I’ll have to ensure I register on time for that one as I will be reading out the title of her thesis. Our first cohort of MSc students will graduate then too.
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.
The views presented here are personal and not necessarily those of my employer (or anyone else for that matter).
Feel free to comment on any of the posts on this blog but comments may be moderated; anonymous comments and any considered by me to be vexatious and/or abusive and/or defamatory will not be accepted. I do not necessarily endorse, support, sanction, encourage, verify or agree with the opinions or statements of any information or other content in the comments on this site and do not in any way guarantee their accuracy or reliability.
In the Dark 