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Two New Publications at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , , , , , , , on August 31, 2024 by telescoper

I am back in circulation after my little break and, since it’s Saturday, I will resume blogging with another report on activity at the  Open Journal of Astrophysics.  Since the last update we have published two more papers, taking  the count in Volume 7 (2024) up to 71 and the total published by OJAp up to 186.  We’ve still got a few in the pipeline waiting for the final versions to appear on arXiv so I expect we’ll reach the 200 mark fairly soon.

The first paper of the most recent pair, published on August 26th 2024,  is “Impact of lensing of gravitational waves on the observed distribution of neutron star masses”  by Sofia Canevarolo, Loek van Vonderen and Nora Elisa Chisari, all of Utrecht University in the Netherlands. This article presents a discussion of the bias in neutron star mass determinations caused by gravitational lensing of the gravitational waves they produceThe paper is in the folder marked Cosmology and NonGalactic Astrophysics.

Here is a screen grab of the overlay which includes the abstract:

 

You can click on the image of the overlay to make it larger should you wish to do so. You can find the officially accepted version of the paper on the arXiv here.

The second paper has the title “FORGE’d in FIRE III: The IMF in Quasar Accretion Disks from STARFORGE” and was published (in the early hours of the morning) on 29th August 2024. The authors, all based in the USA, are Philip F. Hopkins (Caltech), Michael Y. Grudic (Carnegie Observatories), Kyle Kremer (Caltech), Stella S. R. Offner (UT Austin), David Guszejnov (UT Austin) and Anna L. Rosen (UCSD). This paper, which is in the folder marked Astrophysics of Galaxies, presents a numerical study of star formation and the initial mass function in quasar accretion disks. The previous two papers in this series have also been published in the OJAp: you can find them here and here; images and movies related to this project can be found here.

Here is a screen grab of the overlay which includes the abstract:

 

You can click on the image of the overlay to make it larger should you wish to do so. You can find the officially accepted version of the paper on the arXiv here.

That concludes this week’s update. We still have quite a few papers in the pipeline after the summer lull so I expect I’ll have a larger update for you next week!

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Coming of Age in a Low-Density Universe

Posted in Biographical, Open Access, The Universe and Stuff with tags , , , , on August 25, 2024 by telescoper

I was reminded just now that 30 years ago today, on 25th August 1994, this review article by myself and George Ellis was published in Nature (volume 370, pp. 609–615).

Sorry for the somewhat scrappy scanned copy. The article is still behind a paywall. No open access for the open Universe!

Can this really have been 30 years ago?

Anyway, that was the day I officially became labelled a “crank”, by some, although others thought we were pushing at an open door. We were arguing against the then-standard cosmological model (based on the Einstein – de Sitter model), but the weight of evidence was already starting to shift. Although we didn’t predict the arrival of dark energy, the arguments we presented about the density of matter did turn out to be correct. A lot has changed since 1994, but we continue to live in a Universe with a density of matter much lower than the critical density and our best estimate of what that density is was spot on.

Looking back on this, I think valuable lessons would be learned if someone had the time and energy to go through precisely why so many papers at that time were consistent with a higher-density Universe that we have now settled on. Confirmation bias undoubtedly played a role, and who is to say that it isn’t relevant to this day?

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New Publication at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , on August 24, 2024 by telescoper

It’s Saturday morning so it’s time for the usual weekly update of publications at the Open Journal of Astrophysics. Once again this week’s report will be short because there is only one paper to report this week, being  the 69th paper in Volume 7 (2024)  and the 184th  altogether. It was published on Wednesday 21st August 2024.

This week has been a bit strange, actually. We have actually accepted four papers that I was expecting to publish this week but only one has been published because the authors of the others have not yet put the final versions on arXiv. I suppose this is due to ongoing holidays and they’ll appear in due course. The other thing that happened was that when I published the paper below I discovered that the Crossref system was down for a scheduled upgrade that took a whole day to complete. Although I published the paper on 21st August I couldn’t register the metadata, etc, until 22nd August. Just as well I didn’t have more to do really!

Anyway, the title of the latest paper is is The compact circumstellar material of SN 2024ggi: another supernova with a pre-explosion effervescent zone and jet-driven explosion and it  is in the folder marked High-Energy Astrophysical Phenomena. The author is Noam Soker of Technion, Haifa, in Israel; the paper presents a possible explanation of then properties of recently-observed supernova SN 2024ggi.

Here is the overlay of the paper containing the abstract:

 

 

You can click on the image of the overlay to make it larger should you wish to do so. You can also find the officially accepted version of the paper on the arXiv here.

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Newgrange and JWST

Posted in History, The Universe and Stuff with tags , , on August 18, 2024 by telescoper

Although I won’t myself be able to attend, I’m happy to be able to use the medium of this blog to advertise the above public event which is taking place in the first week of September on the back of a week-long conference to celebrate the career of Professor Tom Ray of the Dublin Institute for Advanced Studies. That in turn follows hard on the heels of the Irish National Astronomy Meeting (INAM) which takes place in Galway on 29th and 30th August.

Anyway, the public event on 3rd September is free to attend but you need to register here, where it is described thusly:

The Newgrange Passage Tomb, a prehistoric monument in County Meath, Ireland, is one of the most remarkable examples of Neolithic art and architecture, dating back to around 3200 BC. This ancient structure, with its intricate stone carvings and precise alignment with the winter solstice sunrise, reflects the sophisticated astronomical knowledge of its builders.

With starkly different technology, the James Webb Space Telescope (JWST), launched in 2021, represents the pinnacle of modern astronomical achievement. JWST is designed to peer into the farthest reaches of the universe, capturing images and data from the formation of the earliest galaxies to the atmospheres of planets outside of/beyond our solar system.

Despite being separated by millennia, both Newgrange and JWST underscore humanity’s enduring quest to understand our place in the cosmos through the study of the stars and the universe.

As part of the celebration of the career of Professor Tom Ray the Dublin Institute for Advanced Studies and the Institute of Physics are delighted to host a public event on Newgrange and JWST. This is in recognition of Tom’s long interest in archaeoastronomy and Newgrange in particular, and his involvement with the JWST through the Mid-Infrared instrument (MIRI).

The talk will be delivered by Dr. Frank Prendergast, archaeoastronomer and Emeritus Research Fellow at Technological University Dublin, and Professor Gillian Wright, European Principal Investigator of MIRI and Director of the UK Astronomy Technology Centre in Edinburgh.

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New Publication at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , on August 17, 2024 by telescoper

It’s Saturday morning and time for the usual weekly update of publications at the Open Journal of Astrophysics. This will be a short post because there is only one paper to report this week, being  the 68th paper in Volume 7 (2024)  and the 183rd  altogether. It was published on Thursday August 15th 2024.

The title of the latest paper is is “Spatial segregation of massive clusters in a simulation of colliding dwarf galaxies” and it  is in the folder marked Astrophysics of Galaxies. The authors are Bruce Elmegreen (IBM, NY, USA) and Natalia Lahen (MPA Garching, Germany);  the paper presents a numerical study of the properties and spatial distribution of star clusters resulting from a collision between dwarf galaxies.

Here is the overlay of the paper containing the abstract:

 

 

You can click on the image of the overlay to make it larger should you wish to do so. You can also find the officially accepted version of the paper on the arXiv here.

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Evolving Dark Energy or Supernovae Systematics?

Posted in The Universe and Stuff with tags , , , , , , , on August 15, 2024 by telescoper

A few months ago I posted an item about the release new results from the Dark Energy Spectroscopic Instrument (DESI). That was then followed by a presentation explaining the details which you can find here to find out more about the techniques involved. At the time the new DESI results garnered a lot of media attention much of it about claims that the measurements provided evidence for “New Physics”, such as evolving dark energy. Note that the DESI results themselves did not imply this. Only when combined with supernova measurements did this suggestion arise.

Now there’s a new preprint out by George Efstathiou of Cambridge. The abstract is here:

Recent results from the Dark Energy Spectroscopic Instrument (DESI) collaboration have been interpreted as evidence for evolving dark energy. However, this interpretation is strongly dependent on which Type Ia supernova (SN) sample is combined with DESI measurements of baryon acoustic oscillations (BAO) and observations of the cosmic microwave background (CMB) radiation. The strength of the evidence for evolving dark energy ranges from ~3.9 sigma for the Dark Energy 5 year (DES5Y) SN sample to ~ 2.5 sigma for the Pantheon+ sample. Here I compare SN common to both the DES5Y and Pantheon+ compilations finding evidence for an offset of ~0.04 mag. between low and high redshifts. Correcting for this offset brings the DES5Y sample into very good agreement with the Planck LCDM cosmology. Given that most of the parameter range favoured by the uncorrected DES5Y sample is discrepant with many other cosmological datasets, I conclude that the evidence for evolving dark energy is most likely a result of systematics in the DES5Y sample.

Here are a couple of figures from the paper illustrating the difference in parameter constraints using the uncorrected (left) and corrected (right) Dark Energy (Survey) 5 year Supernova sample.

The y-axis shows a parameter wa, which is zero in the standard model with non-evolving dark energy; the non-zero value implied by the left hand panel using the uncorrected data.

Just as with the Hubble Tension I blogged about yesterday, the evidence for a fundamental revision of our standard model may be nothing of the sort but some kind of systematic error. I think we can expect a response from the Dark Energy Survey (DES) team. Grab your popcorn.

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Hubble Tension Reduced?

Posted in The Universe and Stuff with tags , , , , on August 14, 2024 by telescoper

Back in April I posted about a meeting at the Royal Society in London called Challenging the Standard Cosmological Model, some of which I attended virtually. In that post I mentioned that Wendy Freedman gave a talk related to the ongoing issue of the Hubble Tension, i.e. the discrepancy between different types of measurement of the Hubble Constant, usually characterized as local measurements (using stellar distance indicators) and larger-scale measurements (chiefly Planck). There are quite a few posts about this issue on this blog. Anyway, Wendy Freedman mention in her talk that her latest work on stellar distances suggested a value of 69.1 ± km s-1 Mpc-1, which reduces the tension with Planck significantly. At the time, however, there was no paper explaining how this number was derived.

Yesterday there appeared on arXiv a preprint by Freedman et al. which summarizes the recent results. The abstract is here:

We present the latest results from the Chicago Carnegie Hubble Program ( CCHP) to measure the Hubble constant using data from the James Webb Space Telescope (JWST). This program is based upon three independent methods: (1) Tip of the Red Giant Branch (TRGB) stars, (2) JAGB (J-Region Asymptotic Giant Branch) stars, and (3) Cepheids. Our program includes 10 nearby galaxies, each hosting Type Ia supernovae (SNe Ia), suitable for measuring the Hubble constant (H0). It also includes NGC  4258, which has a geometric distance, setting the zero point for all three methods. The JWST observations have significantly higher signal-to-noise and finer angular resolution than previous observations with the Hubble Space Telescope (HST). We find three independent values of H0 = 69.85 ± 1.75 (stat) ± 1.54 (sys) for the TRGB, H0 = 67.96 ± 1.85 (stat) ± 1.90 (sys)  km s-1 Mpc-1 for the JAGB, and H0 = 72.05 ± 1.86 (stat) ± 3.10 (sys) for Cepheids. Tying into SNe Ia, and combining these methods adopting a flat prior, yields our current estimate of H0 = 69.96 ± 1.05 (stat) ± 1.12 (sys)  km s-1 Mpc-1. The distances measured using the TRGB and the JAGB method agree at the 1% level, but differ from the Cepheid distances at the 2.5-4% level. The value of H0 based on these two methods with JWST data alone is H0 = 69.03 ± 1.75 (total error)  km s-1 Mpc-1. These numbers are consistent with the current standard ΛCDM model, without the need for the inclusion of additional new physics. Future JWST data will be required to increase the precision and accuracy of the local distance scale.

You can read the full paper on arXiv here. A summary of the summary is that of the three methods they use, two give lower values of the Hubble constant and one (Cepheids) gives a higher value but with larger errors. The number quoted in the Royal Society talk was presumably preliminary as it doesn’t match any of the numbers in the abstract, but the point remains.

You can see the reduction in scatter in the new JWST measurements in this Figure (old on the left and new on the right).

On the face of it, these results suggest that the Hubble tension is greatly reduced. I am sure, however, that advocates of a higher value will have been preparing their ripostes and it’s just a matter of time before they arrive on the arXiv too!

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The Mechanics of the Pole Vault

Posted in Sport, The Universe and Stuff with tags , , , on August 11, 2024 by telescoper

One of the many highlights of the 2024 Olympics was the amazing achievement of Armand Duplantis in winning the Gold Medal in Pole Vault and in the process breaking his own world record at a height of 6.25m. Here he is

He seemed to clear that height quite comfortably, actually, so I dare say he’ll break quite a few more records in his time. On the other hand, when I first wrote about this back in 2011 the world record for the pole vault was held by the legendary Ukrainian athlete Sergey Bubka at a height of 6.14m which he achieved in 1994. That record stood for almost 20 years but has since been broken several times since. The fact that the world record has only increased by 11 cm in 30 years tells you that the elite pole vaulters are working at the limits of what the human body can achieve. A little bit of first-year mechanics will convince you why, as I have pointed out in previous posts (e.g. here).

What a pole-vaulter does is rather complicated and requires a lot of strength, flexibility and skill, but as in many physics problems one can bypass the complications and just look at the beginning and the end and use an energy conservation argument. Basically, the pole is a device that converts the horizontal kinetic energy of the vaulter \frac{1}{2} m v^2,  as he/she runs in, to the gravitational potential energy m g h acquired at the apex of his/her  vertical motion, i.e. at the top of the vault.

Now assume that the approach is at the speed of a sprinter, i.e. about 10 ms^{-1}, and work out the height h = v^2/2g that the vaulter can gain if the kinetic energy is converted with 100% efficiency. Since g = 9.8 \, ms^{-2} the answer to that little sum turns out to be about 5 metres.

This suggests that  6.25 metres should not just be at, but beyond, the limit of a human vaulter,  unless the pole were super-elastic. However, there are two things that help. The first is that the centre of mass of the combined vaulter-plus-pole does not start at ground level; it is at a height of a bit less than 1m for an an average-sized person.  Note also that the centre of mass of pole (which weighs about 15 kg and is about 5 m long) only ends up about 2.5 m off the ground when it is vertical, so there’s a significant effect there.  Note also that the centre of mass of the vaulter does not actually pass over the bar after letting go of the pole.  That  doesn’t happen in the high jump, either. Owing to the flexibility of the athlete’s back, the arc is such that the centre of mass remains under the bar while the different parts of the athlete’s body go over it.

Moreover, it’s not just the kinetic energy related to the horizontal motion of the vaulter that’s involved. A human can jump vertically from a standing position using elastic energy stored in muscles. In fact the world record for the standing high jump is an astonishing 1.9m. In the context of the pole vault it seems likely to me that this accounts for at least a few tens of centimetres.

Despite these complications, it is clear that pole vaulters are remarkably efficient athletes. And not a little brave either – as someone who is scared of heights I can tell you that I’d be absolutely terrified being shot up to 6.25 metres on the end of  a bendy stick, even with something soft to land on!

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Three New Publications at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , , , , , , , , , on August 10, 2024 by telescoper

It’s Saturday so it’s time once again for another roundup of business at the  Open Journal of Astrophysics. After last week’s summer lull, this week I have three papers to announce, which brings the total we have published so far this year (Vol. 7) to 67 and the total published by OJAp to 182.

First one up, published on 7th August 2024, is “Brightest Cluster Galaxy Offsets in Cold Dark Matter” by Jonathan Katz of Washington University (St Louis, Missouri, USA),  a simulation-based study of the distribution of the position of brightest cluster galaxies relative to the dark matter distribution and its possible use as a cosmological probe.  The authors are Cian Roche (MIT), Michael McDonald (MIT), Josh Borrow (MIT), Mark Vogelsberger (MIT), Xuejian Shen (MIT), Volker Springel (MPA Garching), Lars Hernquist (Harvard), Ruediger Pakmor (Harvard), Sownak Bose (Durham, UK) and Rahul Kannan (York U., Canada). This paper is in the folder marked Astrophysics of Galaxies.

Here is a screen grab of the overlay, which includes the abstract:

 

 

You can read the paper directly on arXiv here.

The second paper to present is “LAMOST J1010+2358 is not a Pair-Instability Supernova Relic” by five authors based in the USA: Pierre Thibodeaux (Chicago), Alexander P. Ji (Chicago), William Cerny (Yale), Evan N. Kirby (Notre Dame) and Joshua D. Simon (Carnegie Observatories) .  As the title makes clear, the paper presents arguments against previous claims that a particular star is not a pair-instability supernova relic. This paper is in the folder marked Solar and Stellar Astrophysics. It was published on Friday August 9th 2024.

The overlay looks like this:

 

 

 

You can read this paper directly on the arXiv here.

Last, but by no means least, comes  “A Pilot Search for Gravitational Self-Lensing Binaries with the Zwicky Transient Facility“, results of a trial search for signals of gravitational lensing of one component in a binary system by a compact companion, with a discussion of future prospects for larger surveys. This one, which was also published on 9th August, is in the folder marked High-Energy Astrophysical Phenomena. The authors are Allison Crossland & Eric C Bellm (U. Washington), Courtney Klein (UC Irvine), James R. A. Davenport (U. Washington), Thomas Kupfer (Hamburg Observatory) and Steven L. Groom, Russ R. Laher & Reed Riddle (Caltech).

Here is a screengrab of the overlay:

To read the accepted version of this on the arXiv please go here.

That’s it for this week. I hope to post another update next weekend.

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A Physics Question

Posted in Literature, The Universe and Stuff on August 8, 2024 by telescoper
Frank Benson in the role of Coriolanus (1893)

Is Shakespeare’s play Coriolanus different when performed in the Southern Hemisphere?

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