Archive for Cosmology

Astrophysics & Cosmology Masterclass at Maynooth

Posted in Education, Maynooth, The Universe and Stuff with tags , , on February 23, 2021 by telescoper

Regular readers of the blog – both of them – may remember that we planned to present a Masterclass in Astrophysics & Cosmology on January 14th 2021 but this had to be postponed due to Covid-19 restrictions. After today’s announcements by the Government of  a phased return to school starting on March 1st we have now decided to proceed with a new date of March 25th 2021.

This will be a half-day virtual event via Zoom. It’s meant for school students in their 5th or 6th year of the Irish system, who should be returning to classrooms on March 15th, but there might be a few of them or their teachers who see this blog so I thought I’d share the news here. You can find more information, including instructions on how to book a place, here.

Here is the updated official poster and the programme:

I’ll be talking about cosmology early on, while John Regan will talk about black holes. After the coffee break one of our PhD students will talk about why they wanted to study astrophysics. Then I’ll say something about our degree programmes for those students who might be interested in studying astrophysics and/or cosmology as part of a science course. We’ll finish with questions either about the science or the study!

Cosmology Talks: Alvaro Pozo on Potential Evidence for Wave Dark Matter

Posted in The Universe and Stuff with tags , , , , , , , , , on February 19, 2021 by telescoper

It’s time I shared another one of those interesting cosmology talks on the Youtube channel curated by Shaun Hotchkiss. This channel features technical talks rather than popular expositions so it won’t be everyone’s cup of tea but for those seriously interested in cosmology at a research level they should prove interesting. This is quite a recent one, from about a week ago.

In the talk, Alvaro Pozo tells us about a recent paper where he an collaborators detect the transition between a core (flat density profile) and halo (power law density profile) in dwarf galaxies. The full core + halo profile matches very closely what is expected in simulations of wave dark matter (sometimes called “fuzzy” dark matter), by which is meant dark matter consisting of a particle so light that its de Broglie wavelength is long enough to be astrophysically relevant. That is, there is a very flat core, which then drops off suddenly and then flattens off to a decaying power-law profile. The core matches the soliton expected in wave dark matter and the halo matches an outer NFW profile expected outside the soliton. They also detect evidence for tidal stripping of the matter in the galaxies. The galaxies closer to the centre of the Milky Way have their transition point between core and halo happen at smaller densities (despite the core density itself not being systematically smaller). The transition also appears to happen closer to the centre of the galaxy, which matches simulations. Of course the core+halo pattern they have clearly observed might be due to something else, but the match between wave dark matter simulations and observations is impressive. An important  caveat is that the mass for the dark matter that they use is very small and in significant tension with Lyman Alpha constraints for wave-like dark matter. This might indicate that the source of this universal core+halo pattern they’re observing comes from something else, or it might indicate that the wave dark matter is more complicated than represented in the simplest models.

P. S. The papers that accompany this talk can be found here.

P.P.S. If you’re interested in wave dark matter there is a nice recent review article by Lam Hui here.

New Publication at the Open Journal of Astrophysics

Posted in Open Access, The Universe and Stuff with tags , , , , , on February 18, 2021 by telescoper

Time to announce another publication in the Open Journal of Astrophysics. This one was published yesterday, actually, but I didn’t get time to post about it until just now. It is the second paper in Volume 4 (2021).

The latest publication is entitled Characterizing the Sample Selection for Supernova Cosmology and is written by Alex G. Kim on behalf of the LSST Dark Energy Science Collaboration.  It’s nice to be getting papers from large collaborations like this!

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

You can click on the image to make it larger should you wish to do so. You can find the arXiv version of the paper here. This is one for the Cosmology and Nongalactic Astrophysics folder.

New Publication at the Open Journal of Astrophysics

Posted in Open Access, The Universe and Stuff with tags , , , , , , , on February 2, 2021 by telescoper

Time to announce the first publication of 2021 in the Open Journal of Astrophysics. This one was actually published a few days ago but  it took a bit of time to get the metadata and DOI registered so I held off announcing it until that was done.

The latest publication is a lengthy and comprehensive review article (67 pages altogether) by Allahverdi et al. which has 26 authors from all round the world. It is entitled The First Three Seconds: a Review of Possible Expansion Histories of the Early Universe and is a study of the various possible evolutionary histories of cosmic expansion possible with a wide range of cosmological models with their implications for baryogenesis, nucleosynthesis, primordial gravitational wave production, and many other things besides.

Here is a screen grab of the overlay:

You can click on the image to make it larger should you wish to do so. You can find the arXiv version of the paper here. This is one for the Cosmology and Nongalactic Astrophysics folder.

And so Volume 4 begins. Volume 3 had 15 papers, Volume 2 had 12 , and Volume 1 just 4 so we’re growing slowly but surely! Let’s see how many we publish in 2021. I can tell you  we have some very exciting papers in the pipeline…

Postponed: Astrophysics & Cosmology Masterclass at Maynooth

Posted in Education, Maynooth, The Universe and Stuff with tags , , on January 10, 2021 by telescoper

Regular readers of this blog may recall that the Department of Theoretical Physics at Maynooth University  planned to host a Masterclass in Astrophysics & Cosmology on January 14th 2021 (i.e. next Thursday). Unfortunately the closure of schools in Ireland until at least the end of January has given us no alternative but to postpone this event. It’s not cancelled though and we intend to run it as soon as possible: the date is now set provisionally for 25th February.  Limited places remain available and bookings are still open. You can find more information, including instructions on how to book a place, here.

Here is the official poster and the programme (timings still apply, but not the date..):

I’ll be talking about cosmology early on, while John Regan will talk about black holes. After the coffee break one of our PhD students will talk about why they wanted to study astrophysics. Then I’ll say something about our degree programmes for those students who might be interested in studying astrophysics and/or cosmology as part of a science course. We’ll finish with questions either about the science or the courses.

For updates please follow the Department’s on twitter-feed:

New Publication at the Open Journal of Astrophysics

Posted in Open Access, The Universe and Stuff with tags , , , , , , , , , , , , on December 24, 2020 by telescoper

Just time before Christmas to announce another paper in the Open Journal of Astrophysics. This one was actually published a few days ago but because of holiday delays it took some time to get the metadata and DOI registered so I held off announcing it until that was done.

The latest publication is by my colleague* John Regan (of the Department of Theoretical Physics at Maynooth), John Wise (Georgia Tech), Tyrone Woods (NRC Canada), Turlough Downes (DCU), Brian O’Shea (Michigan State) and Michael Norman (UCSD). It is entitled The Formation of Very Massive Stars in Early Galaxies and Implications for Intermediate Mass Black Holes and appears in the Astrophysics of Galaxies section of the arXiv.

Here is a screen grab of the overlay:

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

I think that will be that for for 2020 at the Open Journal of Astrophysics. We have published 15 papers this year, up 25% on last year. Growth is obviously modest, but there’s obviously a lot of inertia in the academic community. After the end of this year we will have two full consecutive years of publishing.

I’d like to take this opportunity to thank all our authors, readers, referees, and editors for supporting the Open Journal of Astrophysics and wish you all the very best for 2021!

*Obviously, owing to the institutional conflict I recused myself from the editorial process on this paper.

New Publication at the Open Journal of Astrophysics

Posted in Open Access, The Universe and Stuff with tags , , , , , , , on December 15, 2020 by telescoper

The Christmas rush is definitely upon us and papers are queuing up to be published in the Open Journal of Astrophysics. The latest publication is by Tom Kitching and Anurag Deshpande of MSSL (University College London) and Peter Taylor of JPL (Caltech). It is entitled Propagating residual biases in masked cosmic shear power spectra. This is another one for the folder marked Cosmology and Nongalactic Astrophysics.

Here is a screen grab of the overlay:

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

When I last posted about a new OJA paper I mentioned that it seemed to be taking authors longer than usual to make revisions. There are signs now that some authors are trying to get papers off their desk before the Christmas break so we may have two or three more to publish before the year is out.

P.S. Last week I received an offer from a commercial organization to buy the Open Journal of Astrophysics. I replied politely that it is not for sale.

New Publication at the Open Journal of Astrophysics!

Posted in Open Access, The Universe and Stuff with tags , , , , , , on December 10, 2020 by telescoper

Time to announce another new paper in the Open Journal of Astrophysics. The latest publication is by Johan Comparat and 27 others – too numerous to list individually here –  and is entitled Full-sky photon simulation of clusters and active galactic nuclei in the soft X-rays for eROSITA. This is another one for the Cosmology and Nongalactic Astrophysics folder.

This paper is closely connected to the eROSITA instrument which is why it involves a considerable number of authors in different institutions – the current record length for an OJAp author list – though this is by no means a large collaboration by the standards of astrophysics and cosmology! It’s good to see some big names in there though!

Here is a screen grab of the overlay:

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

With this paper we have exceeded the number of papers published last year. We do in fact have quite a few in the pipeline but owing to the ongoing pandemic there have been some refereeing delays and in some cases authors are taking more time than expected to do the “revise and resubmit” routine. I think there are plenty of other people around who are just as tired as I am! Perhaps we’ll see a clutch emerging in the New Year!

Cosmology Talks: Eiichiro Komatsu & Yuto Minami on Parity Violation in the Cosmic Microwave Background

Posted in Cardiff, Maynooth, The Universe and Stuff with tags , , , , , , , , on December 2, 2020 by telescoper

It’s time I shared another one of those interesting cosmology talks on the Youtube channel curated by Shaun Hotchkiss. This channel features technical talks rather than popular expositions so it won’t be everyone’s cup of tea but for those seriously interested in cosmology at a research level they should prove interesting.

In this video, Eiichiro Komatsu and Yuto Minami talk about their recent work, first devising a way to extract a parity violating signature in the cosmic microwave background, as manifested by a form of birefringence. If the universe is birefringent then E-mode polarization would change into B-mode as electromagnetic radiation travels through space, so there would be a non-zero correlation between the two measured modes. They  try to measure this correlation using the Planck 2018 data, getting  a 2.4 sigma `hint’ of a result.

A problem with the measurement is that systematic errors, such as imperfectly calibrated detector angles,  could mimic the signal. Yuto and Eiichiro’s  idea was to measure the detector angle by looking at the E-B correlation in the foregrounds, where light hasn’t travelled far enough to be affected by any potential birefringence in the universe. They argue that this allows them to distinguish between the two types of measured E-B correlation. However, this is only the case if there is no intrinsic correlation between the E-mode and B-mode polarization in the foregrounds, which may not be the case, but which they are testing. The method can be applied to any of the plethora of CMB experiments currently underway so there will probably be more results soon that may shed further light on this issue.

Incidentally this reminds me of Cardiff days when work was going on about the same affect using the Quad instrument. I wasn’t involved with Quad but I do remember having interesting chats about the theory behind the measurement or upper limit as it was (which is reported here). Looking at the paper I realize that paper involved researchers from the Department of Experimental Physics at Maynooth University.

P. S. The paper that accompanies this talk can be found here.

Cosmological Non-Linearities as an Effective Fluid

Posted in The Universe and Stuff with tags , , , , , , , on November 27, 2020 by telescoper

We know our Universe is inhomogeneous, comprising regions of high density (galaxies and clusters of galaxies) as well as regions of much lower density (e.g. cosmic voids). Our standard cosmological models are based on exact solutions of Einstein’s equations of general relativity that assume homogeneity and isotropy. The general assumption is that if we confine ourselves to large enough scales the effect of the clumpiness of matter can either be disregarded or treated using perturbation theory. As far as we can tell, that approach works reasonably well but we know it must fail on smaller scales where the structure is in the non-linear regiome where it can’t be described accurately using perturbation theory because the fluctuations are so large.

From time to time I’ve idly wondered whether it might be possible to understand the effect of these non-linearities in general relativity by treating them as a kind of fluid with an energy-momentum tensor that acts as a correction to that of the perfect fluid form of the background cosmological model. This would have to be done via some sort of averaging so it would be an effective, coarse-grained description rather than an exact treatment. It is clear though that non-linearities would generate departures from the perfect fluid form, particularly resulting in off-diagonal terms in the energy-momentum tensor corresponding to anisotropic stresses (e.g. viscosity terms).

Anyway, a recent exchange on Twitter relating to a new paper that has just appeared revealed that far cleverer people than me had looked at this in quite a lot of detail a decade ago:

You can find the full paper here.

There are quite a lot of subtleties in this – how to do the spatial averaging, how to do the time-slicing, etc – which I don’t fully understand but at least I’m reassured that it isn’t a daft idea to try thinking of things this way!

P.S. The relativistic simulations reported in this paper could in principle be used to estimate the parameters mentioned in the abstract above, if that hasn’t been done before!