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Four New Publications at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , , , , , , , on September 29, 2024 by telescoper

A day later than has been usual for such things, it’s now time for a quick update of activity at the Open Journal of Astrophysics. This week we have published another batch of four papers which takes the count in Volume 7 (2024) up to 81 and the total published altogether by OJAp up to 196. I think there may come a week in we publish papers on every day of that week, but it was not this week…

In chronological order, 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.

First one up is “Finding the unusual red giant remnants of cataclysmic variable mergers” by Nicholas Z. Rui and Jim Fuller of California Institute of Technology (Caltech), USA. It presents a discussion of the possible photometric, astroseismological, and surface abundance signatures of red giants formed by mergers of cataclysmic variable stars. It was published on 23rd September 2024 and is in the folder marked Solar and Stellar Astrophysics.

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

 

 

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

The second paper to announce, also published on 23rd September 2024, is “Notes on the Practical Application of Nested Sampling: MultiNest, (Non)convergence, and Rectification” by Alexander Dittmann (U. Maryland, USA). A critical analysis of the MultiNest algorithm together with suggestions for approving its applicability. It is in the folder Instrumentation and Methods for Astrophysics.

You can see the overlay here:

 

 

The accepted version of this paper can be found on the arXiv here.

The third paper, published on 24th September 2024 in the folder marked High-Energy Astrophysical Phenomena, is called  “Merger Precursor: Year-long Transients Preceding Mergers of Low-mass Stripped Stars with Compact Objects” and is by Daichi Tsuna, Samantha Wu & Jim Fuller (Caltech), Yize Dong (UCLA) and Anthony Piro (Carnegie Observatories), all based in the USA.

Here is the overlay

 

 

The final version accepted on arXiv is here.

Last in this batch is “Spectroscopic Observations of the GALEX Nearby Young Star Survey Sample. I. Nearby Moving Group Candidates” by Navya Nagananda (Rochester, NY, USA), Laura Vican (UCLA), Ben Zuckerman (UCLA), David Rodriguez (STScI), Alexander Binks (Tübingen, Germany) & Joel Kastner (Rochester). It describes investigations of the spectra of the GALNYSS sample of over 2000 young stars and the assignment of these stars into moving groups. It is is in the folder marked Solar and Stellar Astrophysics, and was published on 25th September 2024 with this overlay:

 

You can find the official accepted version on the arXiv here.

That’s all for now. I will post another update in a week.

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Dark Matter from Primordial Black Holes?

Posted in The Universe and Stuff with tags , , , , , , , , , on September 27, 2024 by telescoper

We live in a cyclic universe of a sort because every few years somebody tries to resurrect the idea that dark matter is somehow related to primordial black holes, i.e. black holes formed in the very early stages of the history of the Universe so that they have masses much smaller than black holes formed more recently by the collapse of stars or the merger of other black holes. If it forms very early the mass of a PBH could in principle be very small, much less than a star or a planet. The problem with very small black holes is that they evaporate very quickly via Hawking Radiation so would not survive the 14 billion years or so needed to still be in existence today and able to be dark matter.

An idea that was used in the past to circumvent this issue was that something might stop Hawking Radiation proceeding to reduce the mass of a PBH to zero, leaving a relic of finite mass usually taken to be the Planck mass. The suggestion has returned in different (but still speculative) guise recently, fueling a number of media articles of varying degrees of comprehensibility, e.g. here. The technical papers on which these articles are based can be found here and here.

Fortunately, there is now one of those excellent Cosmology Talks explaining the latest idea of how Hawking Radiation might break down and what the consequences are for Primordial Black Holes as a form of Dark Matter.

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Autumnal Equinox 2024

Posted in Biographical, Education, Maynooth, The Universe and Stuff with tags on September 22, 2024 by telescoper

The Autumnal Equinox (in the Northern hemisphere) takes place this afternoon (Sunday 22nd September 2024)  at 13.44 Irish Summer Time (12.44 UT).

Although  the term `equinox’  refers to a situation in which day and night are of equal length, which implies that it’s a day rather than a specific time, the astronomical equinox is more accurately defined by a specific event, i.e. when the plane defined by Earth’s equator passes through the centre of the Sun’s disk (or, if you prefer, when the centre of the Sun passes through the plane defined by Earth’s equator). Day and night are not necessarily exactly equal on the equinox, but they’re the closest they get. From now on days in the Northern hemisphere will be shorter than nights and they’ll get shorter still until the Winter Solstice on 21st December 2024 at 9.21am Irish Time.

Many people take the autumnal equinox to be the end of summer. There is a saying around these parts, however, that `Summer is Summer to Michaelmas Day’ (September 29th), which is not until next week. I must say, though, though it doesn’t feel particularly summery this morning although we did have good weather for most of last week. Looking back over my posts on past occurrences of the Autumnal Equinox, it is notable how many talk about a period of good weather around this time of year. The Welsh phrase Haf Bach Mihangel (Michael’s Little Summer) refers to this kind of spell.

I’ve often remarked how the academic year at Maynooth is largely defined by the astronomical phenomena of the equinoxes and solstices. This year demonstrates this perfectly: Semester 1 lectures for undergraduates begin tomorrow (23rd September), the day after the Autumnal equinox; they end on 20th December, the day before the Winter Solstice. The half-term study break coincides with Samhain, a cross-quarter day. It’s all refreshingly pagan.

This time last year I was getting ready to travel to Barcelona. My sabbatical started on 1st September but I didn’t actually leave for Spain until 24th September. That all seems a very long time ago now, and my sabbatical is well and truly over. I resume teaching next week, though my first lectures (a double session of Engineering Mathematics) are not until Tuesday. I hope I can remember how to teach! I’m also doing Differential Equations and Complex Analysis for 4th Year Mathematical Physics students, but the lectures for that are a bit later (Thursday and Friday). I have taught neither of these modules before, so I am a bit apprehensive.

I now know what I’ll be teaching next Semester too. I’m returning to Computational Physics 1, which I taught for 5 years before my sabbatical, so that’s a familiar one. I’m also doing Particle Physics for 4th year students. I taught a full module in that at Nottingham and a half-module in Cardiff so it’s not exactly new but I haven’t lectured in the subject since about 2010. Has anything important happened in that field since then? I assume that had there been, for example, any new boson discovered I would have heard about it…

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In Search of Stokes V

Posted in The Universe and Stuff with tags , , , , on September 17, 2024 by telescoper

Many moons ago I went to a seminar on the design of an experiment to measure the polarization of the cosmic microwave background. At the end of the talk I asked what seemed to me to be an innocent question. The point of my question was the speaker had focussed entirely on measuring the intensity of the radiation (I) and the two Stokes Parameters that measure linear polarization of the radiation (usually called Q and U). How difficult, I asked, would it be to measure the remaining Stokes parameter V (which quantifies circular polarization)?

There was a sharp intake of breath among the audience and the speaker responded with a curt “the cosmic microwave background is not circularly polarized”. It is true that in the standard cosmological theory the microwave background is produced by Thomson scattering in the early Universe which produces partial linear polarization, so that Q and U are non-zero, but not circular polarization so V=0. I knew that, but had asked my question because I had an idea that it might be worth measuring V (or at least putting an upper limit on it) in order to assess the level of instrumental systematics (which are a serious issue with polarization measurements). It might also help constrain variations from the standard model too.

Well, that thought came back today when I saw a new paper on the arXiv with the abstract:

V-mode polarization of the cosmic microwave background is expected to be vanishingly small in the ΛCDM model and, hence, usually ignored. Nonetheless, several astrophysical effects, as well as beyond standard model physics could produce it at a detectable level. A realistic half-wave plate – an optical element commonly used in CMB experiments to modulate the polarized signal – can provide sensitivity to V modes without significantly spoiling that to linear polarization. We assess this sensitivity for some new-generation CMB experiments, such as the LiteBIRD satellite, the ground-based Simons Observatory and a CMB-S4-like experiment. We forecast the efficiency of these experiments to constrain the phenomenology of certain classes of BSM models inducing mixing of linear polarization states and generation of V modes in the CMB. We find that new-generation experiments can improve current limits by 1-to-3 orders of magnitude, depending on the data combination. The inclusion of V-mode information dramatically boosts the sensitivity to these BSM models.

arXiv:2409.10424

It seems it might be feasible to measure Stokes V after all!

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16 Years In The Dark

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

I just received the following message from WordPress.com reminding me that today is the 16th anniversary of my registration with them, which is when I took my first step into the blogosphere. That was way back on 15th September 2008…

I actually wrote my first post on the day I registered but, unfortunately, I didn’t really know what I was doing on my first day at blogging – no change there, then – and I didn’t actually manage to figure out how to publish this earth-shattering piece. It was only after I’d written my second post that I realized that the first one wasn’t actually visible to the general public because I hadn’t pressed the right buttons, so the two appear in the wrong order in my archive. Such was the inauspicious beginning of this “shitty WordPress blog”!

Since then I have published 6,974 blog posts posts which have altogether received over 5.5M page views. That doesn’t include the 2000+ subscribers who receive posts by email. The largest number of hits I have received in a single day is still 8,864 (in 2014, at the peak of the BICEP2 controversy). The most popular post in the last year was this one.

P.S. Blog traffic had been slow recently, but has increased dramatically in the past few days, perhaps because of the ban on access to it from Maynooth University campus…

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What is Weak Gravitational Lensing?

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

I haven’t posted anything about the European Space Agency’s Euclid mission recently but I can remedy that today by sharing a new video that describes one of the methods that Euclid will use to map the dark Universe. Here’s the video:

Here are the credits

Credit: ESA/Euclid Consortium/Cacao Cinema

License: ESA Standard Licence

And here’s the explainer that goes with it:

ESA’s Euclid mission is surveying the sky to explore the composition and evolution of the dark Universe. But how can Euclid see the invisible? Watch this video to learn about the light-bending effect that enables scientists to trace how dark matter is distributed in the Universe.

By making use of Euclid’s flagship simulation, the video illustrates how dark-matter filaments subtly alter the shape of galaxies. Light travelling to us from vastly distant galaxies is bent and distorted by concentrations of matter along its way. The effect is called gravitational lensing because matter (both ‘normal’ and dark matter) acts as a kind of magnifying glass.

Scientists distinguish between strong and weak gravitational lensing. In strong gravitational lensing distortions of background galaxies or other light sources are very apparent, resulting in arcs, multiple images or so-called Einstein rings. In weak lensing, background sources appear only mildly stretched or displaced. This means we can only detect this effect by analysing large numbers of sources in a statistical way.

The further we look, the more prominent the distortions from weak gravitational lensing are, because there are more dark-matter structures acting as lenses between us and the light sources.

Euclid will measure the distorted shapes of billions of galaxies over 10 billion years of cosmic history, providing a 3D view of the dark matter distribution in our Universe. This will shed light on the nature of this mysterious component.

The map of the distribution of galaxies over cosmic time will also teach us about dark energy, which affects how quickly the Universe expands. By charting the Universe’s large-scale structure in unprecedented detail, Euclid will enable scientists to trace how the expansion has changed over time.

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Four New Publications at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , , , , , , , , , , , , , , on September 14, 2024 by telescoper

Once again, it’s time for a quick update of activity at the Open Journal of Astrophysics. This week we have published another batch of four papers which takes the count in Volume 7 (2024) up to 77 and the total published altogether by OJAp up to 192. Things are picking up again after the summer lull, and we’re moving towards a double century. If we keep up a steady average of four per week we’ll be at 200 per year.

In chronological order, 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.

First one up is “Quasi-two-dimensionality of three-dimensional, magnetically dominated, decaying turbulence” by Shreya Dwivedi, Chandranathan Anandavijayan, and Pallavi Bhat of TIFR, Bangalore, India. The paper presents an analysis of numerical simulations of MHD turbulence using Minkowski Functionals, with implications for local anisotropies revealed therein. It was published on 9th September 2024 and is in the folder marked High-Energy Astrophysical Phenomena.

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

 

 

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

The second paper to announce, also published on 9th September 2024, is “mochi_class: Modelling Optimisation to Compute Horndeski In class” by  Matteo Cataneo (Universität Bonn, Germany) and Emilio Bellini (SISSA, Trieste, Italy). This article presents a cosmological Einstein-Boltzmann solver adapted to work with Horndeski gravity, together with validation tests. It is in the folder Cosmology and NonGalactic Astrophysics.

You can see the overlay here:

 

The accepted version of this paper can be found on the arXiv here.

The third paper, published on 11th September 2024 in the folder marked High-Energy Astrophysical Phenomena, is by Jonathan Katz of Washington University, St Louis, USA. The title is “The Sources of Fast Radio Bursts” and it presents a discussion of the possible physical origin of Fast Radio Bursts, arguing that they fall into two distinct groups.

 

The final version accepted on arXiv is here.

Last in this batch, but by no means least, is “RMS asymmetry: a robust metric of galaxy shapes in images with varied depth and resolution” by Elizaveta Sazonova (U. Waterloo, Canada) with 15 other authors spread around the world (in Canada, USA, Australia, Italy, Chile, UK, Poland, Mexico, Germany, and Spain). This paper presents a method of quantifying distortion of galaxy images connected with mergers or other instabilities. It is in the folder marked Astrophysics of Galaxies and was published on September 12th 2024 with this overlay:

 

You can find the official accepted version on the arXiv here.

That’s all for now. I will post another update in a week.

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Space Week in Maynooth!

Posted in Maynooth, The Universe and Stuff with tags , on September 12, 2024 by telescoper
Euclid View of the Perseus Cluster

The annual Space Week in Ireland is from October 4th – 10th this year. As we have done for the previous couple of years, we will be putting on an event at Maynooth University. When I say “we”, I mean the Department of Physics collectively – I was away in Barcelona at the time of last year’s event so couldn’t give a talk, but I did one the year before. I’ll be doing a talk this year too. The description of my talk reads:

Two of the greatest mysteries in modern science concern the nature of the dark matter and dark energy we think dominate the Universe. In this talk I will explain how the European Space Agency’s Euclid mission, launched last year, is designed to shed light on the “dark side” of the cosmos, present some of the early results, and show how you can get involved in analyzing Euclid data.

Anyway, this year’s event will be on Wednesday 9th October. The event is open is open to all and will be held in the picturesque surroundings of the TSI building. Tickets are free but must be reserved in advance. You can do that here. The event has sold out for both the last two years – with over 400 attendees – so it’s best to book early!

Register on Eventbrite

You can find more details about the programme here. It may change so I’ll post the final programme nearer the event.

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An Anniversary of a Century

Posted in Open Access, The Universe and Stuff with tags on September 11, 2024 by telescoper

While I remember, here is a quick post to mark the fact that the 100th paper at the Open Journal of Astrophysics was published a year ago today (on 11th September 2023).

In the year that has passed since that milestone we have published a further 91 papers. I expect we will pass the 200 mark sometime next month. It’s an accelerating Universe!

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A Question of String Theory

Posted in The Universe and Stuff on September 7, 2024 by telescoper

The answer to the question is that “it’s as long as a piece thereof..”

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