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Weekly Update from the Open Journal of Astrophysics – 21/02/2026

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags AM Canum Venaticorum, AM CVn binary stars, arXiv:2506.09533v2, arXiv:2508.13296v4, arXiv:2509.22779v4, arXiv:2509.23278v2, arXiv:2601.00945v2, arXiv:2601.08524v2, astrophysical jets, Astrophysics of Galaxies, binary stars, Cosmic Dawn, Cosmic Velocities, Cosmology, Cosmology and NonGalactic Astrophysics, Diamond Open Access, Diamond Open Access Publishing, DIPLODOCUS, galaxy formation, galaxy haloes, gamma-ray burst, GRB 250702B, Great Attractor, High-Energy Astrophysical Phenomena, Instrumentation and Methods for Astrophysics, large-scale structure of the Universe, Open Access, Open Access Publishing., Open Journal of Astrophysics, Solar and Stellar Astrophysics, Square Kilometre Array, Square Kilometre Array Observatory, Ultra-long Gamma-ray burst on February 21, 2026 by telescoper

It’s Saturday once more so time for another update of activity at the Open Journal of Astrophysics. Since the last update we have published a further six papers, bringing the number in Volume 9 (2026) to 36 and the total so far published by OJAp up to 484.

I will continue to include the posts made on our Mastodon account (on Fediscience) to encourage you to visit it. Mastodon is a really excellent service, and a more than adequate replacement for X/Twitter (which nobody should be using); these announcements also show the DOI for each paper.

The first paper to report this week is “SKA-Low simulations for a cosmic dawn/epoch of reionisation deep field” by Anna Bonaldi, Philippa Hartley, Simon Purser & Omkar Bait (SKAO, UK), Eunseong Lee (U. Manchester, UK), Robert Braun (SKAO), Florent Mertens (Sorbonne Université, France), Andrea Bracco (Osservatorio Astrofisico di Arcetri, IT), Wendy Williams (SKAO) and Cath Trott (Curtin U., Australia). This paper presents a simulation of an SKA-Low cosmic dawn/epoch of reionisation observation to advance foreground-mitigation approaches: the simulation includes various sky components and modelled errors, allowing for efficacy assessment. It was published on Monday 16th February in the folder Cosmology and Nongalactic Astrophysics.

The overlay is here:

You can find the officially accepted version on arXiv here and the announcement on Fediverse here:

The second paper is “V717 Andromedae: An Active Low Mass Ratio Contact Binary” by Surjit S. Wadhwa (Western Sydney U. Australia), Marko Grozdanovic (Astronomical Observatory Belgrade, Serbia), and Nicholas F.H Tothill, Miroslav D. Filipovic, Ain Y. De Horta (Western Sydney U.). This was also published on Monday 1th February, but in the folder Solar and Stellar Astrophysics. The article discusses the contact binary V717 Andromedae, an extreme low mass ratio system with high inclination and moderate contact, showing signs of chromospheric activity but stable and not a merger candidate

The overlay for this one is here:

The official version of the paper can be found on arXiv here and the Fediverse announcement here:

Next, published on Tuesday 17th February in the folder High-Energy Astrophysical Phenomena, is “DIPLODOCUS II: Implementation of transport equations and test cases relevant to micro-scale physics of jetted astrophysical sources” by Christopher N Everett (Oxford U., UK), Marc Klinger-Plaisier (U. Amsterdam, NL) and Garret Cotter (Oxford). This one discusses further applications of DIPLODOCUS, which is a framework developed for particle distribution transport, with its numerical implementation detailed in Diplodocus.jl. It uses a new sampling technique and is tested on micro-scale physical effects. The first paper in the series can be found here.

The overlay is here:

The official version can be found on arXiv here and the Fediverse announcement is here:

The fourth paper this week, also published on Tuesday 17th February, but in the folder Cosmology and Nongalactic Astrophysics is “Revisiting the Great Attractor: The Local Group’s streamline trajectory, cosmic velocity and dynamical fate” by Richard Stiskalek (Oxford U., UK), Harry Desmond (U. Portsmouth, UK), Stuart McAlpine (Stockholm, SE), Guilhem Lavaux (Sorbonne Université, FR), Jens Jasche (Stockholm) and Michael J. Hudson (U. Waterloo, Canada). This paper revisits the so-called “Great Attractor” concept, finding that it doesn’t dominate the Local Group’s cosmic velocity; multiple structures contribute to the motion, with no single attractor accounting for the flow.

Here is the overlay:

The official version can be found on arXiv here and the Fediverse announcement is here:

The fifth paper this week, is “JWST observations of three long-period AM CVn binaries: detection of the donors and hints of magnetically truncated disks” by Kareem El-Badry (Caltech), Antonio C. Rodriguez (CfA Harvard), Matthew J. Green (U. Oklahoma) & Kevin B. Burdge (MIT); all based in the USA. The article was published on Thursday 19th February 2026 in the folder Solar and Stellar Astrophysics. The paper describes high-cadence infrared spectroscopy used to analyze three long-period, eclipsing AM CVn (AM Canum Venaticorum) binaries; findings suggest the presence of magnetized white dwarf accretors, with surface magnetic fields of 30-100 kG.

The overlay is here:

The accepted version can be found on arXiv here, and the fediverse announcement is here:

Finally for this week we have “Ultra-long Gamma-ray Bursts from Micro-Tidal Disruption Events: The Case of GRB 250702B” by Paz Beniamini (Open University, IL), Hagai B. Perets (Technion, IL) and Jonathan Granot (Open University, IL); all based in Israel. The paper was published on Friday 18th February 2026 in the folder High-Energy Astrophysical Phenomena.

The overlay is here:

You can find the officially accepted version on arXiv here and the Mastodon announcement is here:

And that concludes this week’s update. I will do another next Saturday, by which time I expect we will have published a similar number of papers to this week.

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Weekly Update from the Open Journal of Astrophysics – 14/02/2026

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags arXiv:2507.20190v2, arXiv:2508.00611v3, arXiv:2509.02316v4, arXiv:2510.00440v3, arXiv:2511.01506v2, arXiv:2511.14912v2, Astrophysics of Galaxies, cosmological inference, Cosmology, Cosmology and NonGalactic Astrophysics, Diamond Open Access, Diamond Open Access Publishing, entropy, Faraday Depolarization, Forbush decreases, Fractal Markers, galaxy formation, galaxy haloes, Instrumentation and Methods for Astrophysics, Interstellar Medium, large-scale structure of the Universe, LOFAR, Nebular Emission, Open Access, Open Access Publishing., Open Journal of Astrophysics, Power spectrum, self-interacting dark matter, stellar accretion, supermassive black holes, The Open Journal of Astrophysics on February 14, 2026 by telescoper

It’s Saturday once more so time for another update of activity at the Open Journal of Astrophysics. Since the last update we have published a further six papers, bringing the number in Volume 9 (2026) to 30 and the total so far published by OJAp up to 478.

The first paper to report this week is “Faraday Depolarization Study of a Radio Galaxy Using LOFAR Two-metre Sky Survey: Data Release 2” by Samantha Sneha Paul and Abhik Ghosh (Banwarilal Bhalotia College, India). This was published on Tuesday February 10th in the folder Cosmology and Nongalactic Astrophysics. The paper analyzes the depolarization of radio galaxy ILTJ012215.21+254334.8 using LOFAR’s Sky Survey data, revealing a preferred three-component model and highlighting turbulence in the magneto-ionic medium.

The overlay is here:

You can find the officially accepted version on arXiv here and the announcement on Fediverse here:

The second paper is “Rapid cosmological inference with the two-loop matter power spectrum” by Thomas Bakx (Utrecht U., NL), Henrique Rubira (Ludwig-Maximilians-Universität, DE), Nora Elisa Chisari (Utrecht) and Zvonimir Vlah (Ruđer Bošković Institute, Croatia). This was also published on Tuesday February 10th in the folder Cosmology and Nongalactic Astrophysics. This paper uses the COBRA method to compute the two-loop effective field theory power spectrum of dark matter density fluctuations, providing more precise cosmological constraints than the one-loop EFT.

The overlay for this one is here:

The official version of the paper can be found on arXiv here and the Fediverse announcement here:

Next, published on Wednesday 11th February in the folder Astrophysics of Galaxies, is “Interpreting nebular emission lines in the high-redshift Universe” by Aswin P. Vijayan (U. Sussex, UK) and 9 others based in the UK, Taiwan, China and The Netherlands. This article examines the reliability of diagnostics used to estimate star formation rate and gas-phase oxygen abundance in high-redshift galaxies. It finds that variations in stellar populations and star-dust geometry. The overlay is here:

The official version can be found on arXiv here and the Fediverse announcement is here:

The fourth paper this week, also published on Wednesday 11th February, but in the folder Instrumentation and Methods for Astrophysics is “Derivative-Aligned Anticipation of Forbush Decreases from Entropy and Fractal Markers” by Juan D. Perez-Navarro & David Sierra Porta (Universidad Tecnológica de Bolívar, Colombia). The paper presents a feature-based framework for predicting Forbush decreases, i.e. rapid, temporary drops in galactic cosmic ray (GCR) intensity (up to tens of percent) caused by solar wind disturbances, typically Coronal Mass Ejections (CMEs) or high-speed streams from coronal holes, in neutron-monitor records using various computational methods. The approach is reproducible, operates on native station units, and is stable.

Here is the overlay:

The official version can be found on arXiv here and the Fediverse announcement is here:

The fifth paper, the penultimate for this week, is “Supermassive black hole growth from stellar binary encounters” by Aubrey L Jones and Benjamin C Bromley (University of Utah, USA). This paper explores the growth of supermassive black holes (SMBHs) through stellar accretion via the Hill’s mechanism, predicting capture rates and identifying potential growth drivers in 91 galaxies. It was published on Thursday 11th February 2026 in the folder Astrophysics of Galaxies.

The overlay is here:

The accepted version can be found on arXiv here, and the fediverse announcement is here:

Finally for this week we have “Dynamics in the Cores of Self-Interacting Dark Matter Halos: Reduced Stalling and Accelerated Core Collapse” by Frank C. van den Bosch and Shashank Dattathri (Yale University, USA). This study uses simulations to explore core dynamics in self-interacting dark matter (SIDM) halos. Findings suggest strong self-interactions prevent core stalling and buoyancy, leading to accelerated core collapse. This was published yesterday, on Friday 13th February 2026, in the folder Astrophysics of Galaxies.

The overlay is here:

You can find the published version of the article here, and the Mastodon announcement is here:

And that concludes this week’s update. I will do another next Saturday.

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Probabilistic inference in very large universes

Posted in The Universe and Stuff with tags arXiv:2602.02667, Bayesian probability, Cosmology, large universe, probability on February 10, 2026 by telescoper

I came across a recent article on the arXiv with the title Probabilistic inference in very large universes by Feraz Azhar, Alan H. Guth, Mohammad Hossein Namjoo.

The paper discusses a conceptually challenging issue in cosmology, which I’ll put simply as follows. Suppose we have two cosmological theories: A, which describes a very large universe in only a tiny part of which low-energy physics turns out like ours; and B in which we have a possibly much smaller universe in which low-energy physics is like ours with a high probability. Can we determine whether A or B is the “better” theory, and if so how?

The abstract of the paper is below:

Some cosmological theories propose that the observable universe is a small part of a much larger universe in which parameters describing the low-energy laws of physics vary from region to region. How can we reasonably assess a theory that describes such a mostly unobservable universe? We propose a Bayesian method based on theory-generated probability distributions for our observations. We focus on basic principles, leaving aside concerns about practicality. (We also leave aside the measure problem, to discuss other issues.) We argue that cosmological theories can be tested by standard Bayesian updating, but we need to use theoretical predictions for “first-person” probabilities — i.e., probabilities for our observations, accounting for all relevant selection effects. These selection effects can depend on the observer, and on time, so in principle first-person probabilities are defined for each observer-instant — an observer at an instant of time. First-person probabilities should take into account everything the observer believes about herself and her surroundings — i.e., her “subjective state”. We advocate a “Principle of Self-Locating Indifference” (PSLI), asserting that any real observer should make predictions as if she were chosen randomly from the theoretically predicted observer-instants that share her subjective state. We believe the PSLI is intuitively very reasonable, but also argue that it maximizes the expected fraction of observers who will make correct predictions. Cosmological theories will in general predict a set of possible universes, each with a probability. To calculate first-person probabilities, we argue that each possible universe should be weighted by the number of observer-instants in the specified subjective state that it contains. We also discuss Boltzmann brains, the humans/Jovians parable of Hartle and Srednicki, and the use of “old evidence”.

arXiv:2602.02667

I haven’t had time to read the paper in detail yet, and I don’t think I’m going to agree with all of it when I do, but I found it sufficiently stimulating to share here in the hope that others will find it interesting.

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A Cosmic Miracle?

Posted in OJAp Papers, The Universe and Stuff with tags arXiv:2505.11263v2, Cosmology, galaxy formation, high-redshift galaxy, Lyman Break, z=14.44 on January 30, 2026 by telescoper

A while ago (last May, in fact) I posted an article about a galaxy with an apparent spectroscopic redshift of 14.44. The paper to which that post related had been submitted to the Open Journal of Astrophysics and I haven’t mentioned that paper again until now as the paper was then, so to speak, sub judice. Well, as of today, the paper is now published and will feature in tomorrow’s traditional Saturday roundup of publications at the journal.

This paper was in fact accepted for publication before Christmas, but it took until this morning for the final accepted article to reach the arXiv. Rather awkwardly, the Space Telescope Science Institute issued a press release about this paper on 28th January 2026 stating that the paper was published in the Open Journal of Astrophysics, when that statement was not accurate. As Editor-in Chief of the Open Journal of Astrophysics, I was subsequently contacted by a number of journalists asking where they could find the paper on the OJAp platform. Since it hadn’t been published then I had to say they couldn’t, so a number of pieces (including, for example, this one in Scientific American) have appeared based on the STSCi press release without links to the final version of the paper. It would have been far better, in my opinion, to have delayed the press release until the paper was actually published. It’s better to wait until the ball is in the back of the net before you start celebrating!

Anyway, thanks to me getting up at 6am today, it’s now published so there’s no real harm done.

The fediscience announcement is here:

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

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Dark Energy Survey Year Y6 Results Day!

Posted in The Universe and Stuff with tags Cosmology, Dark Energy, Dark Energy Spectroscopic Instrument, Dark Energy Survey, DES, DES Year 6, DESI on January 22, 2026 by telescoper

This morning’s arXiv announcement contained a number of papers related to the Dark Energy Survey Y6 analysis. There is also a Zoom webinar later today at 10.30 Central Time (16.30 GMT; 13.30 in Greenland). Details can be found here.

You can find links to and abstracts of all the papers here, but I thought it would be useful to provide arXiv links to the latest batch here.

arXiv:2601.14559 Dark Energy Survey Year 6 Results: Cosmological Constraints from Galaxy Clustering and Weak Lensing – this is the key summary paper.
arXiv:2601.14484 Dark Energy Survey Year 6 Results: MagLim++ Lens Sample Selection and Measurements of Galaxy Clustering
arXiv:2601.14864 Dark Energy Survey: DESI-Independent Angular BAO Measurement
arXiv:2601.15175 Dark Energy Survey Year 6 Results: Galaxy-galaxy lensing
arXiv:2601.14833 Dark Energy Survey Year 6 Results: Magnification modeling and its impact on galaxy clustering and galaxy-galaxy lensing cosmology
arXiv:2601.14859 Dark Energy Survey Year 6 Results: Weak Lensing and Galaxy Clustering Cosmological Analysis Framework

A number of DES Y6 papers already published – including several in the Open Journal of Astrophysics – are listed here.

I’ll just highlight a couple of points from the first paper listed above, which uses the now standard “3x2pt” analysis, which combines three complementary two-point correlation functions: cosmic shear; galaxy-galaxy lensing and galaxy clustering. The abstract of this paper is as follows:

A notable result is contained in the last sentence. The simplest interpretation of dark energy is that it is a cosmological constant (usually called Λ) which – as explained here – corresponds to a perfect fluid with an equation-of-state p=wρc² with w=-1. In this case the effective mass density ρ of the dark energy remains constant as the universe expands. To parametrise departures from this constant behaviour, cosmologists have replaced this form with the form w(a)=w₀+w_a(1-a) where a(t) is the cosmic scale factor. A cosmological constant Λ would correspond to a point (w₀=-1, w_a=0) in the plane defined by these parameters, but the only requirement for dark energy to result in cosmic acceleration is that w<-1/3, not that w=-1. Results last year from DESI suggested values of w₀ ≠-1 and w_a≠0 , but the current DES results are consistent with w=-1; they do not constrain w₀ and w_a jointly.

For reference on the left you can find the (w₀, w_a) plane from DESI.

I thought I’d add one of the other cosmological contraint plots:

The results look qualitatively similar to previous plots but the contours have shifted a bit.

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Weekly Update from the Open Journal of Astrophysics – 27/12/2025

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags arXiv:2505.00062v2, arXiv:2507.04987v2, arXiv:2508.10843v2, arXiv:2510.05956v2, Circinus X-1, core-collapse supernovae, Cosmology, Cosmology and NonGalactic Astrophysics, Diamond Open Access, Diamond Open Access Publishing, Earth and Planetary Astrophysics, Fermi Paradox, High-Energy Astrophysical Phenomena, Open Access, Open Journal of Astrophysics, SETI, Solar System, Stability, The Open Journal of Astrophysics, Transverse Velocities on December 27, 2025 by telescoper

I wasn’t planning to do another update this week but I thought it would be best to complete the publications for 2025 at the Open Journal of Astrophysics, so that I don’t have to do a bigger update in the new year, and I have a bit of time this morning, so here we go.

Since the last update we have published four papers which brings the number in Volume 8 (2025) up to 201. Adding the 12 papers in the Supplement, this brings the final total for the year up to 213, and the total so far published by OJAp up to 448. In 2023 we published just 50 papers, so we have more than quadrupled in two years.

The first paper this week is “Transverse Velocities in Real-Time Cosmology: Position Drift in Relativistic N-Body Simulations” by Alexander Oestreicher (University of Southern Denmark), Chris Clarkson (QMUL, UK), Julian Adamek (Universität Zürich, CH) and Sofie Marie Koksbang (U. Southern Denmark). This study uses a general relativistic N-body simulation code to explore how cosmological structures affect position drift measurements, a new method for studying cosmic structure formation and velocity fields. This was published on Tuesday 23rd December 2025 in the folder Cosmology and Nongalactic Astrophysics.

The overlay is here:

You can find the officially accepted version on arXiv here and this is the announcement on Mastodon (Fediscience):

Open Journal of Astrophysics

@OJ_Astro@fediscience.org

New Publication at the Open Journal of Astrophysics: "Transverse Velocities in Real-Time Cosmology: Position Drift in Relativistic N-Body Simulations" by Alexander Oestreicher (University of Southern Denmark), Chris Clarkson (QMUL, UK), Julian Adamek (Universität Zürich, CH) and Sofie Marie Koksbang (U. Southern Denmark)

https://doi.org/10.33232/001c.154744

December 23, 2025, 9:33 am 1 boosts 0 favorites

The second paper of the week is “On the statistical convergence of N-body simulations of the Solar System” by Hanno Rein, Garett Brown and Mei Kanda (U. Toronto, Canada). This study presents numerical experiments to determine the minimum timestep for long-term simulations of the Solar System, finding that timesteps up to 32 days yield physical results. It was published on Tuesday December 23rd in the folder Earth and Planetary Astrophysics.

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

@OJ_Astro@fediscience.org

New Publication at the Open Journal of Astrophysics: "On the statistical convergence of N-body simulations of the Solar System" by Hanno Rein, Garett Brown and Mei Kanda (U. Toronto, Canada)

https://doi.org/10.33232/001c.154745

December 23, 2025, 9:50 am 6 boosts 9 favorites

Next, published on 24th December 2025 in the folder High-Energy Astrophysical Phenomena, we have “The explosion jets of the core-collapse supernova remnant Circinus X-1” by Noam Soker and Muhammad Akashi (Technion, Haifa, Israel). This paper suggests that the rings in the Circinus X-1 supernova remnant resulted from jet-driven explosions, supporting the jittering-jets explosion mechanism theory for core collapse supernovae.

The overlay is here:

The officially accepted paper can be found on arXiv here and the announcement on Mastodon is here

Open Journal of Astrophysics

@OJ_Astro@fediscience.org

New Publication at the Open Journal of Astrophysics: "The explosion jets of the core-collapse supernova remnant Circinus X-1" by Noam Soker and Muhammad Akashi (Technion, Haifa, Israel)

https://doi.org/10.33232/001c.154770

December 24, 2025, 9:15 am 2 boosts 1 favorites

Finally for 2025 we have “Quantifying the Fermi paradox via passive SETI: a general framework” by Matthew Civiletti (City University of New York, USA). This was published on Wednesday 24th December in the folder Instrumentation and Methods for Astrophysics. The author uses SETI observations and the Drake Equation to calculate the probability of detecting at least one extraterrestrial signal, highlighting the model’s limitations and potential improvements. The overlay is here:

The officially accepted version can be found on arXiv here and the Mastodon announcement here:

Open Journal of Astrophysics

@OJ_Astro@fediscience.org

New Publication at the Open Journal of Astrophysics: "Quantifying the Fermi paradox via passive SETI: a general framework" by Matthew Civiletti (City University of New York, USA)

https://doi.org/10.33232/001c.154771

December 24, 2025, 9:27 am 1 boosts 1 favorites

And that concludes the updates for 2025. I’ll be back in a week with the first update of 2026, which will include the first paper(s) of Volume 9.

I’d like to thank everyone who has supported the Open Journal of Astrophysics this year – Editors, Reviewers, Authors and the excellent Library staff at Maynooth – and who have made it such a bumper year. In 2023 we published just 50 papers, so we have more than quadrupled in two years. How many will we publish in 2026?

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R.I.P. Yannick Mellier (1958-2025)

Posted in Euclid, R.I.P., The Universe and Stuff with tags Cosmology, Euclid, Euclid Consortium, Gravitational Lensing, Yannick Mellier on December 21, 2025 by telescoper

Last night I received a message via the Euclid Consortium conveying the very sad news of the death, at the age of 67, of the French astrophysicist and cosmologist Yannick Mellier (pictured left). Among many other things, Yannick was the Euclid Consortium Lead in which role he took on enormous responsibility for getting the project started and, with his team, keeping everything running. His loss is incalculable.

Yannick’s research work focussed on cosmology and the search for dark matter using gravitational lensing. Back in 1987 he was part of the observational team that discovered the first giant arc produced by strong gravitational lensing. He also did pioneering work in the field of weaking gravitational lensing with the Canada-France Hawaii Telescope in that regard starting back in 2000.

For well over a decade now Yannick had been involved with the European Space Agency’s Euclid mission. He was a major force right from the beginning, making the proposal, and after it was accepted leading the Consortium assembled to bring the project into being, preparing for launch, and dealing with the first data. The Euclid Consortium is a huge collaboration and it is impossible to overestimate the scale of the task facing the Lead. The first full data release (DR1) from Euclid will take place towards the end of next year (2026). It is sad beyong words that he did not live to see this.

During the period when I was Chair of the Euclid Consortium Diversity Committee I had a number of interactions with Yannick, sometimes dealing with difficult and confidential matters. I found him to be a man of great wisdom and sensitivity. Despite having many other things to deal with, including a long-term illness, he was unfailingly supportive and his advice was always sound.

The following is an excerpt from the message sent out yesterday:

Yannick’s death leaves a huge void within the consortium and our community. Those of us who have been here the longest know how hard he worked to make the Euclid project a success. He became its embodiment, working tirelessly to ensure its success; we owe him an immense debt of gratitude, and we will surely have the opportunity to reflect in detail on all that we owe him.

Indeed. I hope the Euclid Consortium – and the international cosmological community generally – will, at some stage, organize an appropriate tribute to Yannick.

Rest in Peace, Yannick Mellier (1958-2025)

Ar dheis Dé go raibh a anam

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How magnetism might make galaxies…

Posted in Biographical, The Universe and Stuff with tags Cosmology, galaxy formation, primordial magnetic fields on December 16, 2025 by telescoper

I saw mention of paper recently published in Nature Astronomy by Karsten Jedamzik, Levon Pogosian and Tom Abel with the title Hints of primordial magnetic fields at recombination and implications for the Hubble tension. It’s behind a paywall but there is a version available on the arXiv here. The abstract of the Nature Astronomy version looks like this:

This paper reminded me of a paper I wrote a long time ago (in 1991, when I was at Queen Mary) about primordial magnetic fields and galaxy formation. It had its origins in a lunchtime talk I gave which was based on an old paper from the 1970s by Ira Wasserman. All I did was go through the paper and add a few small comments to update it, including some more recent observational constraints and mentions of dark non-baryonic matter; the Wasserman paper was framed in a model in which all the matter in the Universe was baryonic.

Anyway, the talk went down quite well and I was encouraged to write it up. I did so, and submitted it to a journal (MNRAS). Not unreasonably, it was rejected on the grounds that it didn’t have sufficient original content. I therefore expanded the discussion and submitted it as a review article to Comments on Astrophysics. That journal is now defunct, but the paper can be found on NASA/ADS here. It’s even got some citations!

Here’s the title and abstract:

You can find the whole paper here:

1992ComAp Download

You will see I was advocating a larger magnetic field than in the recent one, with a view to affecting galaxy formation directly rather than larger scale features of the Universe. An important point is that primordial magnetic fields can have a large effect soon after recombination, so they might play a role in the formation of galaxies at high redshift which we are struggling to explain. At least – unlike some of the more exotic explanations that have been proposed – we know that magnetic fields actually exist…

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Everything is a Simple Harmonic Oscillator

Posted in mathematics, The Universe and Stuff with tags cosmic scale factor, Cosmology, Friedman equations, Simple Harmonic Oscillator on December 13, 2025 by telescoper

Anyone who has studied theoretical physics for any time will be familiar with the simple harmonic oscillator, which I will call the SHO for short. This is a system that can be solved exactly and its solutions can be applied in a wide range of situations where it holds approximately, e.g. when looking at small oscillations around equilibrium. I’ve often remarked in lectures that we spend much of our lives solving the SHO problem in various guises, often pretending that the difficult system we have in front of us can, if looked at in the right way, and with sufficient optimism, be approximated by the much simpler SHO. Cue the old joke that if all you have is a hammer, everything looks like nail…

That rambling prelude occurred to me when I found this little problem in some old notes. It is a cute mathematical result that shows that the Friedman equations that underpin our standard cosmological model can in fact be written in the same form as those describing a Simple Harmonic Oscillator. In what follows we take the cosmological constant term to be zero.

The resulting equation is the SHO equation if k>0. I’m not sure whether this result is very useful for anything, but it is cute. It also goes to to show that, if looked at in the right way, the whole Universe is a Simple Harmonic Oscillator!

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Weekly Update from the Open Journal of Astrophysics – 29/11/2025

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags arXiv:2507.01095v3, arXiv:2507.14572v2, arXiv:2507.16707v2, arXiv:2508.06232v2, Astrophysics of Galaxies, chemical abundances, cosmography, Cosmology, Cosmology and NonGalactic Astrophysics, Diamond Open Access, Diamond Open Access Publishing, Fermi-LAT, galaxy mergers, gamma ray, High-Energy Astrophysical Phenomena, Lyman-Alpha Emitters, metallicity, Open Access, Open Access Publishing, Open Journal of Astrophysics, The Open Journal of Astrophysics on November 29, 2025 by telescoper

It’s Saturday again, so it’s time for the usual update of the week’s new papers at the Open Journal of Astrophysics. Publishing this week was interrupted by the Thanksgiving holiday in the United States, which meant there were no arXiv announcements yesterday. Nevertheless, since the last update we have published another four papers, which brings the number in Volume 8 (2025) up to 184, and the total so far published by OJAp up to 419.

The first paper this week is “A theoretical prediction for the dipole in nearby distances using cosmography” by Hayley J. Macpherson (U. Chicago, USA) and Asta Heinesen (Niels Bohr Institute, Denmark). This was published on Monday 24th November 2025 in the folder Cosmology and Nongalactic Astrophysics. It presents a method to predict the dipole in luminosity distances that arises due to nearby inhomogeneities to leading-order correction to the standard isotropic distance-redshift law. Incidentally, I wrote about a talk by one of the authors here.

The overlay is here:

You can find the officially accepted version on arXiv here and the Fediverse announcement is here:

Open Journal of Astrophysics

@OJ_Astro@fediscience.org

New Publication at the Open Journal of Astrophysics: "A theoretical prediction for the dipole in nearby distances using cosmography" by Hayley J Macpherson (U. Chicago, USA) and Asta Heinesen (Niels Bohr Institute, Denmark)

https://doi.org/10.33232/001c.150319

November 24, 2025, 8:25 am 2 boosts 1 favorites

The second paper of the week is “A Targeted Gamma-Ray Search of Five Prominent Galaxy Merger Systems with 17 years of Fermi-LAT Data” by Siddhant Manna and Shantanu Desai (IIT Hyderabad Kandi, India). This one was published on Tuesday November 25th 2025 in the folder marked High-Energy Astrophysical Phenomena. It describes a search for gamma-ray emission in Fermi-LAT data from five merging galaxy systems with marginal detections for two of them

The overlay is here:

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

Next one up is “Metallicity fluctuation statistics in the interstellar medium and young stars – II. Elemental cross-correlations and the structure of chemical abundance space” by Mark R. Krumholz (ANU, Australia), Yuan-Sen Ting (Ohio State U., USA), Zefeng Li (Durham U., UK), Chuhan Zhang (ANU), Jennifer Mead (Columbia U., USA) and Melissa K. Ness (ANU). This was published in the folder Astrophysics of Galaxies on Wednesday November 26th. It presents an extended stochastically-forced diffusion model for the chemical evolution of galaxies, making quantitative predictions for the degree of correlation in abundance patterns in both gas and young stars.

The overlay is here:

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

Open Journal of Astrophysics

@OJ_Astro@fediscience.org

New Publication at the Open Journal of Astrophysics: "Metallicity fluctuation statistics in the interstellar medium and young stars – II. Elemental cross-correlations and the structure of chemical abundance space" by Mark R. Krumholz (ANU, Australia), Yuan-Sen Ting (Ohio State U., USA), Zefeng Li (Durham U., UK), Chuhan Zhang (ANU), Jennifer Mead (Columbia U., USA) and Melissa K. Ness (ANU)

https://doi.org/10.33232/001c.150356

November 26, 2025, 8:34 am 1 boosts 1 favorites

The fourth and final paper of the week is “Simulating realistic Lyman-alpha emitting galaxies including the effect of radiative transfer” by Hasti Khoraminezhad & Shun Saito (Missouri Institute of Science & Technology, USA), Max Gronke (U. Heidelberg, Germany) and Chris Byrohl (MPA Garching, Germany). An empirical model for Lyman-alpha emitters (LAEs) which provides predictions for the halo occupation distributions and relationship between luminosity and halo mass, including the distribution of satellite LAEs. It was published on Thursday November 27th 2025 in the folder Astrophysics of Galaxies.

The overlay is here:

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

Open Journal of Astrophysics

@OJ_Astro@fediscience.org

New Publication at the Open Journal of Astrophysics: "Simulating realistic Lyman-alpha emitting galaxies including the effect of radiative transfer" by Hasti Khoraminezhad & Shun Saito (Missouri Institute of Science & Technology, USA), Max Gronke (U. Heidelberg, Germany) and Chris Byrohl (MPA Garching, Germany)

https://doi.org/10.33232/001c.151254

November 27, 2025, 9:20 am 1 boosts 1 favorites

And that concludes the update for this week. I will do another next Saturday.

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