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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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Two New Publications at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , , , , on September 7, 2024 by telescoper

It’s Saturday morning again so here’s 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 73 and the total published by OJAp up to 188.  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 September 4th 2024,  and in the folder marked Astrophysics of Galaxies, is “Massive Black Hole Seeds”  by John Regan of the Department of Theoretical Physics at Maynooth University and Marta Volonteri (Sorbonne Université, Paris, France). This article presents a discussion of the pathways to the formation of massive black holes, including both light and heavy initial seeds.

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. Those of you who are paying attention will see that there is a bit of a glitch on the left hand side where software has thrown a line break in between the two author names. I have no idea what caused this so I raised a ticket with Scholastica and no doubt it will soon be fixed.  (Update: it is now fixed, 12th September 2024). You can find the officially accepted version of this paper on the arXiv here.

The second paper has the title “The future of cosmological likelihood-based inference: accelerated high-dimensional parameter estimation and model comparison” and was published on 5th September 2024. The authors are Davide Piras (Université de Genève), Alicja Polanska (MSSL) , Alessio Spurio Mancini (Royal Holloway, London), Matthew A. Price(UCL) & Jason D. McEwen (UCL); the latter four are all based in the UK. This paper, which is in  the folder marked Cosmology and NonGalactic Astrophysics, describes an accelerated approach to Bayesian inference in higher-dimensional settings, as required for cosmology, based on recent developments in machine learning and its underlying technology.

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. More  next week!

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The Editorial Board of the Open Journal of Astrophysics

Posted in Open Access, The Universe and Stuff with tags , , on September 6, 2024 by telescoper

A couple of months ago, I issued a call for new Editors of the Open Journal of Astrophysics. That was very successful and we added a number of new Editors. The complete list (of 20 members) follows:

Peter Coles* (Department of Theoretical Physics, Maynooth University, Ireland). Cosmology, astrophysics, statistics and methodology.

Thierry Appourchaux (CNRS, Institut d’Astrophysique Spatiale, Orsay, France). Space instrumentation, astroseismology, helioseismology, statistics and methodology.

Emory (Ted) Bunn (Department of Physics, University of Richmond, USA). Relativity, cosmology.

Walter Dehnen (Astronomisches Rechen-Institut, University of Heidelberg, Germany). Stellar dynamics, galaxy dynamics, galaxies, bars, Milky-Way dynamics, Gaia, numerical methods, N-body techniques, smooth particle hydrodynamics (SPH).

Philipp Edelmann (Los Alamos National Laboratory, New Mexico, USA). Stellar astrophysics, hydrodynamics, high-performance computing, supernovae, internal waves, stellar evolution, numerical methods.

Pedro Ferreira (Department of Physics, University of Oxford, UK). Large-scale structure, general relativity, cosmic microwave background, early universe, cosmology.

Andrew Jaffe (Department of Physics, Imperial College, London, UK). Astrophysics, statistics and methodology, cosmology.

Harley Katz (Department of Astronomy and Astrophysics, University of Chicago, USA). Galaxy formation and evolution, numerical simulations

Lucyna Kedziora-Chudczer (School of Physics, University of New South Wales, Sydney, Australia). Active galactic nuclei, polarimetry, atmospheres of planets, exoplanets, solar system planets.

Julien Larena (Laboratoire Univers et Particules de Montpellier, Université de Montpellier, France). Cosmology, gravitation, lensing, large-scale structure, general relativity.

Manuela Magliocchetti (National Institute of Astrophysics, Rome, Italy). Cosmology, galaxies, active galactic nuclei (AGN).

Sean McGee (Department of Physics & Astronomy, University of Birmingham, UK). Galaxy formation, galaxy clusters, galaxy surveys.

Manolis Plionis (Department of Physics, Aristotle University of Thessaloniki, Greece). Observational cosmology, extragalactic astrophysics, large-scale structure, active galactic nuclei.

Alkistis Pourtsidou (Higgs Centre & Institute for Astronomy, Edinburgh, UK). Cosmology, large-scale structure of the Universe, radio astronomy, galaxy surveys.

Justin Read (School of Mathematics and Physics, University of Surrey, UK). Dark matter, cosmology, galaxy formation and evolution, dwarf galaxies, milky way, galactic dynamics, galactic archaeology, computational modeling.

Hanno Rein (Department of Physics and Environmental Sciences, University of Toronto at Scarborough, Canada). Numerical methods, in particular N-body codes and integration methods for planetary systems, planet formation, stochastic processes, planet migration, celestial mechanics, and Saturn’s rings.

Aleks Scholz (School of Physics & Astronomy, University of St Andrews, UK). Exoplanets, brown dwarfs, protoplanetary disks, stellar evolution, star formation.

Elena Sellentin (Sterrewacht Leiden, Leiden University, The Netherlands). Applied Mathematics, Cosmology, Statistics, Statistical Inference.

Elena Terlevich (Instituto Nacional de Astrofísica, Óptica y Electrónica, Puebla, Mexico). Stellar populations in galaxies, observational cosmology, violent star formation, element abundances, dynamics of stellar systems.

Bingbing Wang (Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, USA.) Particle astrophysics, MHD turbulence, cosmic rays acceleration, cosmic ray propagation in the Galaxy and heliosphere.

Apologies to anyone who volunteered but has not yet received a reply from me. I’ve been a bit preoccupied these last weeks! The call is still open, though. Here are the areas of arXiv covered by the journal:

  1. astro-ph.GA – Astrophysics of Galaxies. Phenomena pertaining to galaxies or the Milky Way. Star clusters, HII regions and planetary nebulae, the interstellar medium, atomic and molecular clouds, dust. Stellar populations. Galactic structure, formation, dynamics. Galactic nuclei, bulges, disks, halo. Active Galactic Nuclei, supermassive black holes, quasars. Gravitational lens systems. The Milky Way and its contents
  2. astro-ph.CO – Cosmology and Nongalactic Astrophysics. Phenomenology of early universe, cosmic microwave background, cosmological parameters, primordial element abundances, extragalactic distance scale, large-scale structure of the universe. Groups, superclusters, voids, intergalactic medium. Particle astrophysics: dark energy, dark matter, baryogenesis, leptogenesis, inflationary models, reheating, monopoles, WIMPs, cosmic strings, primordial black holes, cosmological gravitational radiation
  3. astro-ph.EP – Earth and Planetary Astrophysics. Interplanetary medium, planetary physics, planetary astrobiology, extrasolar planets, comets, asteroids, meteorites. Structure and formation of the solar system
  4. astro-ph.HE – High Energy Astrophysical Phenomena. Cosmic ray production, acceleration, propagation, detection. Gamma ray astronomy and bursts, X-rays, charged particles, supernovae and other explosive phenomena, stellar remnants and accretion systems, jets, microquasars, neutron stars, pulsars, black holes
  5. astro-ph.IM – Instrumentation and Methods for Astrophysics. Detector and telescope design, experiment proposals. Laboratory Astrophysics. Methods for data analysis, statistical methods. Software, database design
  6. astro-ph.SR – Solar and Stellar Astrophysics. White dwarfs, brown dwarfs, cataclysmic variables. Star formation and protostellar systems, stellar astrobiology, binary and multiple systems of stars, stellar evolution and structure, coronas. Central stars of planetary nebulae. Helioseismology, solar neutrinos, production and detection of gravitational radiation from stellar systems.

We are looking for experienced scientists in any of these areas, and it would indeed be useful to have people who can cover a range of subjects (as some of our existing editors do), but there I think we’re still a bit short on High-Energy Astrophysics, Solar and Stellar Physics, and Galactic Astrophysics. I’d also like to see a better gender balance so applications from female scientists are particularly welcomed, as are astrophysicists from geographical areas not currently covered. The Open Journal of Astrophysics is intended to be a global enterprise!

Please follow the instructions here if you would like to volunteer!

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Prize Poster!

Posted in Maynooth, The Universe and Stuff with tags , , , , , on September 1, 2024 by telescoper

I had been looking forward to attending last week’s Irish National Astronomy Meeting in the fine city of Galway but unfortunately I couldn’t go because I had an appointment I couldn’t reschedule (which also kept me offline for a couple of days). This was a shame because it turns out that one of our undergraduate SPUR students at Maynooth, Jake Feeney, together with two colleagues, John Regan and Paddy Kavanagh, won the prize for the best poster at INAM.

Here is the winning poster:

Congratulations to Jake et al!

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