Archive for Cosmology

« Older Entries
Newer Entries »

Two New Publications at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , , , , , , on February 1, 2024 by telescoper

As the first month of 2024 is now over, I thought I’d post an update relating to the  Open Journal of Astrophysics.  Since the last update we have published two papers, taking  the count in Volume 7 (2024) up to 9 (the total for January) and the total published by OJAp up to 124. We will have others soon, but I will be travelling for the first few days of February so the next update will be in a week or so.

Using our sophisticated forecasting algorithm, based on the first month of 2024 as input, I predict that we will publish around 9×12=108 papers in 2024, more than double last year’s total of 50.

Both the current papers discussed here are in the folder marked Cosmology and NonGalactic Astrophysics, our most popular category.

Anyway, the first paper of the most recent pair – published on January 30th – is “Capse.jl: efficient and auto-differentiable CMB power spectra emulation”, by Marco Bonici (INAF Milano, Italy & Waterloo, Canada), Federico Bianchini (Stanford, USA) and Jaime Ruiz-Zapatero (Oxford, UK). This paper presents an emulator for rapid and accurate prediction of Cosmic Microwave Background (CMB) temperature, polarization, and lensing angular power spectra, that works much faster than traditional methods. The code is written in Julia, in which language we are seeing an increasing number of submissions to OJAp.

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 was published yesterday (31st January 2024) and has the title “Cosmological Inflation in N-Dimensional Gaussian Random Fields with Algorithmic Data Compression” which is a  study of inflationary models with Gaussian random potentials for multiple scalar fields, tracking the evolutionary trajectories numerically. The authors are Connor Painter and Emory Bunn, both the Physics Department at the University of Richmond, Virginia (USA). Ted Bunn (as he is usually known) is a longstanding member of the Editorial Board of the Open Journal of Astrophysics (and was thereby excluded from any involvement in the editorial process for this paper).

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.

Here Endeth the Update.

Leave a comment »

Cosmology Discussions

Posted in Uncategorized with tags on January 20, 2024 by telescoper

(Based on an idea stolen from here.)

Leave a comment »

Three New Publications at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , , , , , , , , , , , , on January 20, 2024 by telescoper

As promised yesterday, it’s time for a roundup of the week’s business at the  Open Journal of Astrophysics. This past week we have published three papers, taking  the count in Volume 7 (2024) up to 4 and the total published by OJAp up to 119. There are quite a few more ready to go as people return from the Christmas break.

In chronological order, the three 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 “Prospects for studying the mass and gas in protoclusters with future CMB observations” by  Anna Gardner and Eric Baxter (Hawaii, USA), Srinivasan Raghunathan (NCSA, USA), Weiguang Cui (Edinburgh, UK), and Daniel Ceverino (Madrid, Spain). This paper, published on 17th January 2024, uses realistic hydrodynamical simulations to probe the ability of CMB Stage 4-like (CMB-S4) experiments to detect and characterize protoclusters via gravitational lensing and the Sunyaev-Zel’dovich effect. This paper is in the category of Cosmology and Nongalactic 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 is “SDSS J125417.98+274004.6: An X-ray Detected Minor Merger Dual AGN” and is by Marko Mićić, Brenna Wells, Olivia Holmes, and Jimmy Irwin (all of the University of Alabama, USA).  This presents the discovery of a dual AGN in a merger between the galaxy SDSS J125417.98+274004.6 and dwarf satellite, studied using X-ray observations from the Chandra satellite. The paper was also published on 18th January 2024 in the category Astrophysics of Galaxies . You can see the overlay here:

 

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

The last paper of this batch is  entitled “Population III star formation: multiple gas phases prevent the use of an equation of state at high densities” and the authors are:  Lewis Prole (Maynooth, Ireland), Paul Clark (Cardiff, UK), Felix Priestley (Cardiff, UK), Simon Glover (Heidelberg, Germany) and John Regan (Maynooth, Ireland). This paper, which presents a comparison of results obtained using chemical networks and a simpler equation-of-state approach for primordial star formation (showing the limitations of the latter) was published on 19th January 2024 and also in the folder marked Astrophysics of Galaxies.

Here is the overlay:

 

You can find the full text for this one on the arXiv here.

And that concludes the update. There’ll be more next week!

 

Leave a comment »

The Big Ring Circus

Posted in Astrohype, Bad Statistics, The Universe and Stuff with tags , , , , on January 15, 2024 by telescoper

At the annual AAS Meeting in New Orleans last week there was an announcement of a result that made headlines in the media (see, e.g., here and here). There is also a press release from the University of Central Lancashire.

Here is a video of the press conference:

I was busy last week so didn’t have time to read the details so refrained from commenting on this issue at the time of the announcement. Now that I am back in circulation, I have time to read the details, but unfortunately was unable to find even a preprint describing this “discovery”. The press conference doesn’t contain much detail either so it’s impossible to say anything much about the significance of the result, which is claimed (without explanation) to be 5.2σ (after “doing some statistics”). I see the “Big Ring” now has its own wikipedia page, the only references on which are to press reports, not peer-reviewed scientific papers or even preprints.

So is this structure “so big it challenges our understanding of the universe”?

The Big Ring (blue) and another large structure (red)
Spot the Ring in the actual data

Based on the available information it is impossible to say. The large-scale structure of the Universe comprises a complex network of walls and filaments known as the cosmic web which I have written about numerous times on this blog. This structure is so vast and complicated that it is very easy to find strange shapes in it but very hard to determine whether or not they indicate anything other than an over-active imagination.

To assess the significance of the Big Ring or other structures in a proper scientific fashion, one has to calculate how probable that structure is given a model. We have a standard model that can be used for this purpose, but to simulate very structures is not straightforward because it requires a lot of computing power even to simulate just the mass distribution. In this case one also has to understand how to embed Magnesium absorption too, something which may turn out to trace the mass in a very biased way. Moreover, one has to simulate the observational selection process too, so one is doing a fair comparison between observations and predictions.

I have seen no evidence that this has been done in this case. When it is, I’ll comment on the details. I’m not optimistic however, as the description given in the media accounts contains numerous falsehoods. For example, quoting the lead author:

The Cosmological Principle assumes that the part of the universe we can see is viewed as a ‘fair sample’ of what we expect the rest of the universe to be like. We expect matter to be evenly distributed everywhere in space when we view the universe on a large scale, so there should be no noticeable irregularities above a certain size.

https://www.uclan.ac.uk/news/big-ring-in-the-sky

This just isn’t correct. The standard cosmology has fluctuations on all scales. Although the fluctuation amplitude decreases with scale, there is no scale at which the Universe is completely smooth. See the discussion, for example, here. We can see correlations on very large angular scales in the cosmic microwave background which would be absent if the Universe were completely smooth on those scales. The observed structure is about 400 Mpc in size, which does not seem to be to be particularly impressive.

I suspect that the 5.2σ figure mentioned above comes from some sort of comparison between the observed structure and a completely uniform background, in which case it is meaningless.

My main comment on this episode is that I think it’s very poor practice to go hunting headlines when there isn’t even a preprint describing the results. That’s not the sort of thing PhD supervisors should be allowing their PhD students to do. As I have mentioned before on this blog, there is an increasing tendency for university press offices to see themselves entirely as marketing agencies instead of informing and/or educating the public. Press releases about scientific research nowadays rarely make any attempt at accuracy – they are just designed to get the institution concerned into the headlines. In other words, research is just a marketing tool.

In the long run, this kind of media circus, driven by hype rather than science, does nobody any good.

P.S. I was going to joke that ring-like structures can be easily explained by circular reasoning, but decided not to.

12 Comments »

New Dark Energy Survey Supernovae Results

Posted in The Universe and Stuff with tags , , , , , , , on January 10, 2024 by telescoper

Some important cosmological results have just been announced by the Dark Energy Survey Collaboration. I haven’t had time to go through them in detail but I thought it was worth doing a quick post here to draw attention to them. The results concern a sample of Type Ia supernovae (SN Ia) discovered during the full five years of the Dark Energy Survey (DES) Supernova Program, which contains about 1500 new Type Ia Supernovae that can be used for cosmological analysis. The paper is available on the arXiv here; the abstract is:

The key numerical result of interest is the equation-of-state parameter for dark energy, designated by w, which occurs in the (assumed) relationship between pressure p and effective mass density ρ  of the form p=wρc2. A cosmological constant – which for many cosmologists is the default assumption for the form of dark energy – has w=-1 as I explained here. This parameter is one of the things Euclid is going to try to measure, using different methods. Interestingly, the DES results are offset a bit from the value of -1, but with quite a large uncertainty.

While the results for the equation-of-state parameter are somewhat equivocal, one thing that is clear is that the new SNIa measurements do confirm the existence of dark energy, in that the data can only be described by models with accelerating expansion, as dramatically demonstrated in this Figure:

I think this figure – or versions of it – will very rapidly appear in public talks on cosmology, including my own!

1 Comment »

Euclid in the Media

Posted in Euclid, The Universe and Stuff with tags , , , , , on December 3, 2023 by telescoper

Yesterday came across the above “infographic” – as I’m told such things are called – showing the media traffic generated by last month’s Early Release Observations from the ESA Euclid mission. Some quite interesting facts emerge from it. The new observations were released n 7th November, hence the big spike in the left hand panel on that date.

I see that about 31% of the activity was on Twitter, which I am no longer on, with a slightly smaller amount on Facebook. Overall, social media account for about 60% of the “reach”, with mainstream media (including print, online, and TV/Radio) languishing far behind. Blogs (presumably including this one) account for a mere 1%.

The breakdown by country is interesting too; the table shows only EAS member states. The UK is way out in front, no doubt because BBC News ran a major item on the day of the release. France, Germany, Italy and Spain all have major scientific involvements in Euclid and correspondingly active public engagement activities.

I was pleasantly surprised at the significant amount of interest in Ireland, given that some bigger countries with far greater scientific involvement in Euclid (e.g. Denmark and The Netherlands) generated so little. As the only member of the Euclid Consortium in Ireland I could try to pretend that this was all down to me, but I rather think it’s more likely to be a result of the fact that many Irish people read the UK media so some of the Irish traffic could be spillover from the big UK spike. Still, I think one can interpret this as meaning that the Public in the Republic have an appetite for news about space, something that we have certainly noticed when organizing events in Maynooth.

I thought I’d mention another nice thing. Here is one of the PR images produced by ESA about the early release observations. The point about Euclid is that to achieve its science goals it has to have extremely good optical quality across a very wide field of view. The systems are currently being tested and fine-tuned to see how good their performance actually is, but so far it’s looking good.

The main thing that caught my eye, however, is the collection of little flags along the bottom. How nice it is to see Ireland’s among them!

Leave a comment »

New Publication at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , on December 1, 2023 by telescoper

It’s Friday and I thought I’d take  the opportunity before the weekend to announce yet another new paper at the Open Journal of Astrophysics.

The latest paper is the 46th so far in Volume 6 (2023) – just four to go for a half-century – and it’s the 111th altogether. This one was actually published on Wednesday November 29th.

The title is “Optimization and Quality Assessment of Baryon Pasting for Intracluster Gas using the Borg Cube Simulation” and it presents an algorithm for adding baryons to gravity-only simulations via a “pasting” approach. It is in the folder marked Cosmology and Nongalactic Astrophysics.

There are 8 authors: F. Kéruzoré;  L. Bleem; M. Buehlmann;  J.D. Emberson; N. Frontiere; S. Habib; K. Heitmann; and P. Larsen;  all of them based at the Argonne National Laboratory, in Illinois (USA).

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

Leave a comment »

Hubble Tension Reviewed

Posted in The Universe and Stuff with tags , , on November 24, 2023 by telescoper

Just a quick post to pass on a reference to a paper on arXiv (to appear in Annual Reviews of Astronomy and Astrophysics) about the ongoing saga of the Hubble Tension. The authors are Licia Verde, Nils Schöneberg, and Héctor Gil-Marín, three members of the ICCUB which is hosting me during my sabbatical. I saw an earlier draft of this paper but didn’t want to blog about it before the final version appeared. The abstract (which I’ve slightly reformatted) reads:

The Hubble parameter H0, is not a univocally-defined quantity: it relates redshifts to distances in the near Universe, but is also a key parameter of the ΛCDM standard cosmological model. As such, H0 affects several physical processes at different cosmic epochs, and multiple observables. We have counted more than a dozen H0‘s which are expected to agree if a) there are no significant systematics in the data and their interpretation and b) the adopted cosmological model is correct. With few exceptions (proverbially confirming the rule) these determinations do not agree at high statistical significance; their values cluster around two camps: the low (68 km/s/Mpc) and high (73 km/s/Mpc) camp. It appears to be a matter of anchors: the shape of the Universe expansion history agrees with the model, it is the normalizations that disagree. Beyond systematics in the data/analysis, if the model is incorrect there are only two viable ways to “fix” it: by changing the early time (z≳1100) physics and thus the early time normalization, or by a global modification, possibly touching the model’s fundamental assumptions (e.g., homogeneity, isotropy, gravity). None of these three options has the consensus of the community. The research community has been actively looking for deviations from ΛCDM for two decades; the one we might have found makes us wish we could put the genie back in the bottle.

arXiv:2311.13305


You can read the full paper here to learn about the scientific arguments, but I’d like to draw attention to this excerpt which is of more general relevance and with which I agree wholeheartedly:

It is also fair to say that the developments of the last decade have changed the expectations and modus operandi of a big part of the community. The community now expects results to be reproducible, hence the data and key software to be publicly available in such a way that a practitioner not involved in the original analysis could still retrace and reproduce all important steps and findings. While research areas such as the CMB and large-scale structure made this transition to “open science” about two decades ago, this was not the case for other areas of extra-galactic astronomy, but this is now changing.

arXiv:2311.13305

4 Comments »

Euclid, the Perseus Cluster, and Beyond!

Posted in Euclid, The Universe and Stuff with tags , , , on November 8, 2023 by telescoper

I see that the Euclid Early Release Observation of the Perseus Cluster is today’s Astronomy Picture of the Day:

The Perseus Cluster seen by Euclid

The Perseus Cluster (Abell 426) – a dense concentration of over a thousand galaxies with a total mass of about 1.2 × 1015 M⊙ – is impressive in its own right, especially because the picture was taken in a single exposure, but the staggering thing about this image is that it contains hundreds of thousands of galaxies. In other words there are as many galaxies in this picture as there are words in a book. Most of these galaxies are in the background, not associated with the cluster, and many of them extremely distant. With so many objects in one field, you can perhaps see how much data we will get from the entire survey, which will last more than 6 years. It is these distant sources – billions of them – that Euclid will survey to glean information about the expansion history of the Universe.

P.S. Yesterday’s press conference resulted in a lot of media attention worldwide, even some in Ireland. There is a piece on the RTÉ website, for example, and another on Silicon Republic (which includes a quote from yours truly).

2 Comments »

Euclid Update!

Posted in Euclid with tags , , , on November 6, 2023 by telescoper

Just one more sleep before the first actual science images from European Space Agency’s Euclid mission are released tomorrow. These are called the Early Release Observations (EROs) – they aren’t part of the full survey, but are to demonstrate the performance of the telescope and detectors.

There has been a slight change to the schedule advertised here so the press conference will now take place on Tuesday 7th November at 14.15 Central European (not Summer) Time, CET, which is 13.15 GMT. For more details, see here.

You can watch the press conference on the new ESA Web TV channel or on the Youtube Live Stream. I’ll post a quick update tomorrow after the images go public.

Leave a comment »

« Older Entries
Newer Entries »