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R.I.P. Jayant Narlikar (1938-2025)

Posted in Biographical, R.I.P., The Universe and Stuff with tags , , , , , , on May 20, 2025 by telescoper
Professor Jayant Vishnu Narlikar (1938-2025)

I heard this morning of the death at the age of 86 of renowned Indian cosmologist Jayant Vishnu Narlikar. I understand he died peacefully in his sleep in Pune after a brief illness.

Scientifically, Jayant Narlikar is probably best known for his work with Fred Hoyle on a conformal gravity theory and as an advocate of the Steady State theory of cosmology. In India however his fame extended far beyond the world of research, as an educator and science popularist, as well as Founder-Director of the Inter-University Centre for Astronomy and Astrophysics (IUCAA) in Pune. Those who met him – as I was lucky enough to do – will also remember him as a kind and gracious man, and a self-effacing inspirer of young scientists. During my visit I gave a talk there, which Narlikar attended, and we had a very nice conversation afterwards from which I learnt a huge amount.

The Directorship at IUCAA came with a house which had a very nice lawn, on which I remember playing croquet with Donald Lynden-Bell and others, but that’s another story. Another random thing I remember is that I remember is that Narlikar’s username on the IUCAA email system was “jvn” and he was often referred to informally by that name.

Although he never really abandoned the Steady State cosmology, despite the weight of evidence in favour if the Big Bang, it is to Narlikar’s great credit that he didn’t try to impose his own scientific ideas on those working at IUCAA. In fact he assembled an excellent group of cosmologists and astrophysicists and encourage them to do whatever they liked.

I first visited IUCAA in 1994 to work with Varun Sahni. In those days Westerners mainly went to Pune to visit an ashram (usually the one run by the guru Rajneesh). I remember when I arrived on the train from Mumbai and tried to get a taxi to the IUCAA campus, the driver asked me “which ashram?” I had long hair and a beard at that time, so I looked a potential hippy. I said, “No ashram. Professor Narlikar”. He knew exactly where to take me; “Narlikar” was a household name in India, where the newspapers are awash with tributes today (e.g. here) and where his loss will be keenly felt.

Rest in peace Jayant Narlikar (1938-2025)

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A galaxy at redshift z=14.44?

Posted in OJAp Papers, The Universe and Stuff with tags , , , , , on May 19, 2025 by telescoper

This morning’s arXiv mailing presented me with a distraction from examination marking in the form of a paper by Naidu et al. with this abstract:

This paper has been submitted to the Open Journal of Astrophysics. In the relatively recent past, papers like this about record-breaking galaxies would normally be submitted to Nature so perhaps we’re at last starting to see a change of culture?

I usually feel a bit conflicted in situations when a paper has been submitted for editorial review there. In this case I am posting it here for two reasons: one is that I am not the Editor responsible for this paper; the other is that the arXiv submission specifically says

Submitted to the Open Journal of Astrophysics. Comments greatly appreciated and warmly welcomed!

In order to generate flagging it here to encourage people to comment, either through the box below or by contacting the authors.

For reference, here is the key plot showing the spectrum from which the redshift is determined. It is rather noisy, but the Lyman break seems reasonably convincing and there are some emission lines that appear to offer corroborative evidence:

You might want to read this article (another OJAp paper) which contains this plot showing how galaxies at redshift z>10 challenge the standard model:

Please read the paper and comment if you wish!

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Weekly Update from the Open Journal of Astrophysics – 17/05/2025

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , , , , , , , on May 17, 2025 by telescoper

It’s a lovely Saturday morning in May, and it’s time for the weekly  update of papers published at the Open Journal of Astrophysics. Since the last update we have published four new papers, which brings the number in Volume 8 (2025) up to 59 and the total so far published by OJAp up to 294.

In chronological order of publication, the four papers published this week, with their overlays, are as follows. You can click on the images of the overlays to make them larger should you wish to do so.

The first paper to report is: “Multi-Phase Thermal Structure & The Origin of the Broad-Line Region, Torus, and Corona in Magnetically-Dominated Accretion Disks” by Philip F. Hopkins (Caltech, USA). This was published on Monday May 12th in the folder Astrophysics of Galaxies. It presents simple accretion disk model that predicts the properties of many features including the dusty torus, broad-line region, continuum emission and coronal gas.

The overlay is here:

You can find the officially accepted version on arXiv here.

Second one up is “Sparsity covariance: a source of uncertainty when estimating correlation functions with a discrete sample of observations in the sky” by Pierre Fleury (U. Montpellier, France). This one was published on Tuesday 13th May 2025 in the folder Cosmology and NonGalactic Astrophysics.  This paper presents a discussion of the uncertainty in cosmological observables caused by discrete sampling and a method to compute the covariances resulting from this.

The overlay is here:

You can find the officially-accepted version of the paper on arXiv here.

The third paper of the week, published on Wednesday May 14th 2025,  is “Dark Matter Particle Flux in a Dynamically Self-consistent Milky Way Model” by Lucijana Stanic, Mark Eberlein, Stanislav Linchakovskyy, Christopher Magnoli, Maryna Mesiura, Luca Morf, Prasenjit Saha (University of Zurich, Switzerland) and Eugene Vasiliev (University of Surrey, UK). This one presents a study of the behaviour of dark matter in an anisotropic model for the Milky Way halo with implications for particle detection rates. It is in the folder Astrophysics of Galaxies.

Here is the overlay:

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

The last paper published this week is “Too fast to be single: Tidal evolution and photometric identification of stellar and planetary companions” by Ilay Kamai and Hagai B. Perets (Technion, Haifa, Israel). This one was published on Friday 16th May 2025 in the folder Solar and Stellar Astrophysics. It presents an analysis of the rotation of stars observed in the Kepler field to identify non-single systems with high spin rates resulting from tidal effects.

Here is the overlay:

The official published version can be found on the arXiv here.

That’s all the papers for this week. I’ll post another update next week.

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The CosmoVerse: The White Paper

Posted in The Universe and Stuff with tags , , , on May 16, 2025 by telescoper

Newly announced on arXiv there is a review article with the title The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics. The abridged form of the abstract reads:

The standard model of cosmology has provided a good phenomenological description of a wide range of observations both at astrophysical and cosmological scales for several decades. This concordance model is constructed by a universal cosmological constant and supported by a matter sector described by the standard model of particle physics and a cold dark matter contribution, as well as very early-time inflationary physics, and underpinned by gravitation through general relativity. There have always been open questions about the soundness of the foundations of the standard model. However, recent years have shown that there may also be questions from the observational sector with the emergence of differences between certain cosmological probes. In this White Paper, we identify the key objectives that need to be addressed over the coming decade together with the core science projects that aim to meet these challenges. These discordances primarily rest on the divergence in the measurement of core cosmological parameters with varying levels of statistical confidence. These possible statistical tensions may be partially accounted for by systematics in various measurements or cosmological probes but there is also a growing indication of potential new physics beyond the standard model. After reviewing the principal probes used in the measurement of cosmological parameters, as well as potential systematics, we discuss the most promising array of potential new physics that may be observable in upcoming surveys. We also discuss the growing set of novel data analysis approaches that go beyond traditional methods to test physical models.

arXiv:2504.01669v2

Here’s a plot demonstrating one of the tensions discussed in this paper, and widely on this blog, the Hubble Tension:


This is a very comprehensive review article consisting of over 400 pages and having over 400 authors. I expect all of you to read it over the weekend. There will be a test on Monday.

*One of whom happens to be a PhD student of mine.

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After Lectures and before Examinations

Posted in Education, Maynooth, The Universe and Stuff with tags , , on May 15, 2025 by telescoper

This morning I did my last teaching session of the Academic Year 2024-5, a revision lecture/tutorial on Computational Physics. It was optional, as this is officially a study break, and was at 9am, but I had about 30% attendance which wasn’t bad in the circumstances. As is often the case with optional sessions, I think the students who came were the keenest and probably therefore those who least needed last-minute tips for the examination, but that’s always the way.

The Examination Period starts tomorrow morning, but most of the students who turned up this morning have their first examination on Monday 19th May which happens to be Computational Physics.

Anyway, now that my teaching is over I thought I’d take the opportunity to wish all students the best for their examinations:

You shouldn’t really be relying on luck of course, so here are some tips (especially for physics students, but applicable elsewhere).

  1. Try to get a good night’s sleep before the examination and arrive in plenty of time before the start. Spending all night cramming is unlikely to help you do well.
  2. Prepare well in advance so you’re relaxed when the time comes.
  3. Read the entire paper before starting to answer any questions. In particular, make sure you are aware of any supplementary information, formulae, etc, given in the rubric or at the end.
  4. Start off by tackling the question you are most confident about answering, even if it’s not Question 1. This will help settle any nerves. You’re under no obligation to answer the questions in the order they are asked.
  5. Don’t rush! Students often lose marks by making careless errors. In particular, check all your working out, including numerical results obtained your calculator, at least twice
  6. Please remember the units!
  7. Don’t panic! You’re not expected to answer everything perfectly. A first-class mark is anything over 70%, so don’t worry if there are bits you can’t do. If you get stuck on a part of a question, don’t waste too much time on it (especially if it’s just a few marks). Just leave it and move on. You can always come back to it later.

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Last Remarks

Posted in Biographical, Education, Euclid, Maynooth, The Universe and Stuff, Uncategorized with tags , , on May 11, 2025 by telescoper

On Friday (9th May), the last day of undergraduate teaching at Maynooth, I gave the last lecture in my module on Particle Physics. I actually finished the syllabus on Tuesday (6th) so the final one was more a revision class than a lecture. I used it to go through some past examination questions and (try to) answer some general points raised by the class.

What surprised me about this lecture was that, as has usually been the case, there was more-or-less a full attendance. Examinations in Maynooth start on Friday (May 16th), but the Particle Physics examination is not until May 27th, near the end of the examination period. I therefore expected that many students would be concentrating on their revision for their other modules, which have exams earlier in the season or finishing their projects (which are due in before the exams start). There were one or two absences, but most came anyway. In fact there was even an extra student, one of our MSc students. When I saw him at the back of the lecture hall I asked, jokingly, why he had come. He replied “I haven’t got anything better to do”. I wasn’t sure how to interpret that!

That lecture was at 11am. Later that day, at 3pm, I gave a Departmental colloquium (which had quite a big audience). The title was Euclid: The Story So Far and the abstract was

The European Space Agency’s Euclid satellite was launched on 1st July 2023 and, after instrument calibration and performance verification, the main cosmological survey is now well under way. In this talk I will explain the main science goals of Euclid, give a brief summary of progress so far, showcase some of the science results already obtained, and set out the time line for future developments, including the main data releases and cosmological analysis.

The audience for these talks is very mixed: experimental and theoretical physics staff, postgraduates and even some undergraduate students (including some who were in my lecture earlier) so it was quite a general talk rather than one I might give to an specialist astrophysics audience. If you’re interested you can find the slides here.

Having a quick cup of tea after the end of the talk and before I headed off to catch the train, I talked briefly with a student who is taking his final examinations at Maynooth this year. He told me that I had actually given the first lecture he attended when he had just started his first year and the colloquium was the last talk he would attend at Maynooth. That would be the case for quite a few students in the audience, I suppose, but it won’t be true for any in future: I am no longer teaching any modules taken by first year students, and I’ll be retired when the current first year students graduate…

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Weekly Update from the Open Journal of Astrophysics – 10/05/2025

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , on May 10, 2025 by telescoper

It’s time for another update Saturday morning update of activity at the Open Journal of Astrophysics. After the record-breaking stats described in the last update , this week has been on the slow side with just one paper published. This brings the number in Volume 8 (2025) up to 55 and the total so far published by OJAp up to 290.

The paper to report is “Late-time growth weakly affects the significance of high-redshift massive galaxies” by Qianran Xia & Dragan Huterer (U. Michigan, USA) and Nhat-Minh Nguyen (U. Tokyo, Japan). This paper, which was published on Wednesday 7th May 2025,  is published in the folder Cosmology and NonGalactic Astrophysics. It presents an argument that changes in the growth rate of perturbations at low redshift do not have much effect on predictions of the abundance of lassive galaxies at high redshift.

The overlay is here:

 

You can find the officially accepted version on arXiv here.

That’s all for now. I’ll do another update next week.

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Weekly Update from the Open Journal of Astrophysics – 03/05/2025

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , , , , , , , , , , , , , , on May 3, 2025 by telescoper

Saturday morning once again, and time for another update of papers published at the Open Journal of Astrophysics. It’s been a recording-breaking week: since the last update we have published no fewer than ten papers, which brings the number in Volume 8 (2025) up to 54 and the total so far published by OJAp up to 289.

The first paper to report is “Subspace Approximations to the Focused Transport Equation of Energetic Particles, I. The Standard Form” by B. Kippenstein & A. Shalchi (U. Manitoba, Canada). This paper, which was published on Monday 28th April 2025, presents a hybrid analytical-numerical method to solve the Fokker-Planck equation for the transport of energetic particles. It is published in the folder Solar and Stellar Astrophysics.

The overlay is here:

You can find the officially accepted version on arXiv here.

Next is “The Importance of Subtleties in the Scaling of the ‘Terminal Momentum’ For Galaxy Formation Simulations” by Philip F. Hopkins (Caltech, USA). This presents a technical discussion of issues surrounding the proper modelling of supernova blast waves and their effects in numerical simulations of galaxy formation. It was published on Tuesday 29th April 2025 in the folder Astrophysics of Galaxies. The overlay is here:

The final version can be found on arXic here.

Next one up is “Local variations of the radial metallicity gradient in a simulated NIHAO-UHD Milky Way analogue and their implications for (extra-)galactic studies” by Sven Buder (ANU, Australia), Tobias Buck (U. Heidelberg, Germany), Qian-Hui Chen (ANU) and Kathryn Grasha (ANU). This one was also published on Tuesday 29th April 2025 in the folder Astrophysics of Galaxies. It describes a numerical study of the variation of chemical abundance with radial position in galaxies and the implications of this for galaxy formation. Here is the overlay:

and you can find the final accepted version on arXiv here.

The fourth paper this week is “Zooming In On The Multi-Phase Structure of Magnetically-Dominated Quasar Disks: Radiation From Torus to ISCO Across Accretion Rates” by Philip F. Hopkins (Caltech, USA) and 14 others based in the USA and Canada. This was also published on Tuesday 29th April 2025 in the folder Astrophysics of Galaxies. It presents very detailed numerical study of the structure of magnetized quasar accretion disks. The overlay is here:

You can find the official final version on arXiv here.

Next is “Tomographic halo model of the unWISE-Blue galaxies using cross-correlations with BOSS CMASS galaxies” by Alex Krolewski, Jensen Lawrence, and Will J. Percival (U. Waterloo, Canada). This one was also published on 29th April 2025, which was a busy day(!), but in the folder Cosmology and NonGalactic Astrophysics.  This paper describes using the halo model to create mock samples unWISE-Blue galaxies, applicable to other tomographic cross-correlations between photometric samples and narrowly-binned spectroscopic samples. The overlay is here:

The final version of this one can be found on the arXiv here.

Number six for this week is “StratLearn-z: Improved photo-estimation from spectroscopic data subject to selection effects” by Chiara Moretti (SISSA, Trieste, Italy), Maximilian Autenrieth (Imperial College, UK), Riccardo Serra (SISSA), Roberto Trotta (SISSA), David A. van Dyk (Imperial) and Andrei Mesinger (SNS Pisa, Italy). This was published on Thursday 1st May 2025 in the folder Cosmology and NonGalactic Astrophysics. This one is about estimating photometric redshifts using an approach that relies on splitting the source and target datasets into strata based on estimated propensity score. The overlay is here:

 

The official version can be found on arXiv here.

Next is “The Impact of Galaxy-halo Size Relations on Galaxy Clustering Signals” by Joshua B. Hill and Yao-Yuan Mao (U. Utah, USA). This one was also published on May 2nd 2025 and is in the folder Astrophysics of Galaxies. It discusses the challenge of identifying a specific galaxy halo property that controls galaxy sizes through constraints from galaxy clustering alone. The overlay is here:

You can find the official version of the paper on arXiv here.

The next paper is “Detection of Thermal Emission at Millimeter Wavelengths from Low-Earth Orbit Satellites” by Allen Foster (Princeton, USA) and an international cast of 90 others, which is too many to list individually. This one was also published on Thursday May 1st but is in the folder Instrumentation and Methods for Astrophysics.  The paper discusses the experimental detection of thermal emission from satellites and a discussion of the implications for astrophysical observations, especially time-domain astronomy. The overlay is here:

You can find the final version of the paper on arXiv here.

The penultimate paper of this week is “Pseudo-Cls for spin-s fields with component-wise weighting” by David Alonso (U. Oxford, UK). This one was published yesterday (Friday 2nd May 2025).  The paper presents an approach to power spectrum estimation appropriate for data with anisotropic noise properties or for which complicated masks are required.  It can be found in the folder Cosmology and NonGalactic Astrophysics. The overlay is here:

 

The final version of this paper is on arXiv here.

The last paper this week is “The past, present and future of observations of externally irradiated disks” by Planet formation environments collaboration: Megan Allen (U. Sheffield, UK) and 52 others. This paper was published on Friday 2nd May in the folder Solar and Stellar Astrophysics.  It presents a review of research on the effects of the ultraviolet radiation environment on protoplanetary disc evolution and planet formation. The overlay is here:

You can find the final version on arXiv here.

That’s all the papers for this week. I’ll just add that there were quite a few gremlins at Crossref this week, particularly yesterday. I usually do the publishing first thing in the morning but yesterday’s papers were held in a queue for most of the day pending registration. Usually it just takes a few minutes, but for these I had to wait several hours but we got there in the end. Although ten papers is more than we have ever published in a week, we still haven’t had a week in which we’ve published on every working day!

Anyway, that’s all for this week. I’ll post another update next Saturday.

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Euclid on Sky

Posted in Euclid, The Universe and Stuff with tags , , , on May 2, 2025 by telescoper

I haven’t posted much recently about the European Space Agency’s Euclid Mission but I’ve got an excuse to remedy that today as I’ve just seen that the Special Issue of Astronomy & Astrophysics called Euclid on Sky has at last been published (with a date of 30th April 2025). This contains the main mission and instrument overview papers as well as scientific papers relating to the Early Release Observations. All the individual papers have been on arXiv for some time already.

You can access the Special Issue here.

The main mission overview paper has 1139 authors (including yours truly); that’s definitely the longest author list I’ve ever been on! The arXiv version has been available for almost a year and has already got 254 citations. Here is the abstract:

The current standard model of cosmology successfully describes a variety of measurements, but the nature of its main ingredients, dark matter and dark energy, remains unknown. Euclid is a medium-class mission in the Cosmic Vision 2015-2025 programme of the European Space Agency (ESA) that will provide high-resolution optical imaging, as well as near-infrared imaging and spectroscopy, over about 14,000 deg^2 of extragalactic sky. In addition to accurate weak lensing and clustering measurements that probe structure formation over half of the age of the Universe, its primary probes for cosmology, these exquisite data will enable a wide range of science. This paper provides a high-level overview of the mission, summarising the survey characteristics, the various data-processing steps, and data products. We also highlight the main science objectives and expected performance.

Here’s Figure 1.

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Weekly Update from the Open Journal of Astrophysics – 26/04/2025

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , , , , , , on April 26, 2025 by telescoper

It’s Satuday morning once again, and time for another update of papers published at the Open Journal of Astrophysics. Since the last update we have published two papers, which brings the number in Volume 8 (2025) up to 44 and the total so far published by OJAp up to 279.

The first paper to report is “Approximating non-Gaussian Bayesian partitions with normalising flows: statistics, inference and application to cosmology” by Tobias Röspel, Adrian Schlosser & Björn Malte Schäfer (Universität Heidelberg, Germany) which was published on April 23rd 2025 in the folder Cosmology and NonGalactic Astrophysics. It is an introduction to normalizing flows – a machine learning technique for transforming distributions – and its application to the extraction of cosmological parameters from supernova data.

The overlay is here:

You can find the officially accepted version on arXiv here.

The other paper this week is “Dwarf Galaxies in the TNG50 Field: connecting their Star-formation Rates with their Environments” by Joy Bhattacharyya & Annika H.G. Peter (Ohio State University, USA) and Alexie Leauthaud (UC Santa Cruz, USA).  This one was published on 24th April 2025 in the older Astrophysics of Galaxies and it studies dwarf galaxies with properties similar to the Large and Small Magellanic Clouds that form in different environments in the TNG50 simulation of the IllustrisTNG project.

The overlay is here:

 

and you can find the final accepted version on arXiv here.

 

That’s all for this week. I’ll have another update next Saturday.

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