Another quick update about the release of the Early Release Observations (EROs) from Euclid, due to take place next Tuesday 7th November. For one thing, here is a little taster video.
Five images will be released on Tuesday. I know what the Early Release Observations are but you will have to wait until Tuesday to find out. If I told you now I’d have to kill you…
It’s Sunday but I’ll be a bit busy next week so I’m taking the opportunity today to announce yet another new paper at the Open Journal of Astrophysics. This one was published on Friday 20th October.
The latest paper is the 41st so far in Volume 6 (2023) and the 106th in all. It is a product of the Dark Energy Survey team and the Kilo-Degree Survey Collaboration, which amounts to about 160 authors altogether. The corresponding author for this article was the Astronomer Royal for Scotland Professor Catherine Heymans, no less.
The primary classification for this paper is Cosmology and NonGalactic Astrophysics and its title is “DES Y3 + KiDS-1000: Consistent cosmology combining cosmic shear surveys”. The article presents a joint analysis of the Dark Energy Survey Year 3 data and the Kilo-Degree Survey data, with a discussion of the implications for cosmological parameters. The key figure – a very important one – is this:
If you want to know more about the result and why it is so important you could read the paper. It is, however, rather long: 40 pages including 21 figures and 15 tables. Do not despair, though, because here is a video explaining the work in the series of Cosmology Talks presented by Shaun Hotchkiss:
Anyway, 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.
It’s Friday so it’s a good time to catch up with the week’s action at the Open Journal of Astrophysics, where there have been two new publications so far this week. These papers take us up to a total of 40 in Volume 6 (2023) and 105 in total since we started publishing.
The title of the first paper is “Halo Properties from Observable Measures of Environment: I. Halo and Subhalo Masses” and its primary classification is Astrophysics of Galaxies. it is an exploration using neural networks of how the peak masses of dark matter halos and subhaloes correlate with observationally-accessible measures of their dependence on environment.
The authors based in the United States of America: Haley Bowden and Peter Behroozi of the University of Arizona, and Andrew Hearin of the Argonne National Laboratory
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 on 18th October 2023. The primary classification for this one is Cosmology and Nongalactic Astrophysics and is “Mitigating the noise of DESI mocks using analytic control variates”. For those of you not up with the lingo, DESI stands for the Dark Energy Spectroscopic Instrument and you can read more about it here.
The lead author for this one is Boryana Hadzhiyska of the Lawrence Berkeley Laboratory and the University of California, Berkeley (USA) and there are 32 other authors. This paper presents a method for reducing the effects of sample variance on cosmological simulations using analytical approximations and tests it using DESI data.
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.
Don’t worry about what this is, I’m just testing to see what the video rendering looks like. If you want to know, it’s an attempt to run the collapse of a spherical over-density backwards in time!

It was more than four years ago that I passed on the news that the space mission LiteBIRD had been selected as the next major mission by the Japanese Space Agency JAXA and Institute for Space and Astronautical Science (ISAS).
LiteBIRD (which stands for `Lite (Light) satellite for the studies of B-mode polarization and Inflation from cosmic background Radiation Detection’) is a planned space observatory that aims to detect the footprint of the primordial gravitational waves on the cosmic microwave background (CMB) in a form of a B-mode polarization pattern. This is the signal that BICEP2 claimed to have detected nine years ago to muc excitement, but was later shown to be a caused by galactic dust.
At the time, I said that this was great news for a lot of CMB people all round the world that this mission had been selected – include some old friends from Cardiff University. Well, I’ve just seen a news item announcing a grant to Cardiff astrophysicists who will lead the UK involvement and develop the optical design.
The launch date has slipped into the 2030s (no doubt partly because of the pandemic) so I’ll be long retired before it happens, but the mission will last three years and will, like Euclid, be at Earth-Sun Lagrange point known as L2. It will be a very difficult task to extract the B-mode signal from foregrounds and instrumental artifacts but I wish LiteBIRD every success!
Just after I arrived in Barcelona, I posted a piece about the telescope in the foyer of the Physics Department:
I’m indebted to Vicent Martínez for the following information and the picture:
Ignacio Tarzaona bought the telescope in 1906 for the University of Barcelona from the Grubb factory in Dublin. Sir Howard Grubb (son of Thomas Grubb, founder of the Grubb Telescope Company) and Ignacio Tarazona actually knew each other well. In this photograph taken in Berrocalillo (Spain) on May 28, 1900, we can see both of them. The man farthest to the right of all, standing and wearing a “Catalan barretina” is Ignacio Tarazona and Sir Howard Grubb is sitting in the front row, fifth from left with his Panama hat on his knee.
I almost forgot about this but some new data from the ESA Gaia mission will be announced this afternoon at 3pm CEST*, though it seems to be a bit late. This announcement concerns the latest batch of Gaia Focused Product (Gaia FPR) data. The release consists in the publication of 5 papers on specific aspects of the mission and the associated data. You can watch here. Due to technical problems it has been delayed by 30 minutes and there is a new link:
While waiting to view the announcement, you may wish to familiarize yourself with the mission by reading this list of Top Ten Gaia Facts.
*Coles Extended Sabbatical Time
Time to announce yet another new paper at the Open Journal of Astrophysics. This one was actually published on Friday (6th October 2023), but for one reason and another I’ve only just got around to announcing it here.
The latest paper is the 38th so far in Volume 6 (2023) and the 103rd in all. The authors are: Matthew Price, Matthijs Mars, Matthew Docherty, Alessio Spurio Mancini, Augustin Marignier and Jason McEwen – all affiliated with University College London, UK.
The primary classification for this paper is Cosmology and Nongalactic Astrophysics and its title is “Fast emulation of anisotropies induced in the cosmic microwave background by cosmic strings”. It describes a generative technique for producing generating cosmic microwave background temperature maps using wavelet phase harmonics. For an explanation of what a cosmic string is, see here. If you don’t know the difference between “emulation” and “simulation”, I refer you to the text!
Here is a screen grab of the overlay of the published version 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.
Having settled in to my new apartment on the Gran Via I’ve got time for a another quick update on the European Space Agency’s Euclid mission. For full details about what follows you can see here. Everything I mention here is already in the public domain, so I am not disclosing any secrets!
The last update I posted contained some frustrating and potentially worrisome news: the Performance Verification (PV) phase of the mission had to be put on hold in order to troubleshoot an intermittent problem with the Fine Guidance Sensor (FGS), which is supposed to help to maintain correct pointing of the telescope. This wasn’t working correctly as demonstrated vividly by the following image:
Obviously the survey couldn’t proceed without accurate control of the pointing of the telescope so it was urgently necessary to find out what was going wrong and fix it. It turns out that the software was getting confused by the flashes caused by cosmic ray protons hitting the detectors, think they were the gude stars it was supposed to be steering by. After identifying the problem, new software was written and uploaded to the spacecraft.
I wasn’t sure how this had gone until I saw via an internal communication that the PV phase had restarted. That announcement would not have been made had the upgrade not worked and sure enough it has now been made public that all is well. Congratulations to the instrumentation and software teams for this success. They’ve been working phenomenally hard on this.
There was an additional problem with stray light in the telescope that I have also mentioned before. That was only an issue for specific orientations of the telescope and has been dealt with by simply redesigning the survey a little to minimize the occurrence of the effect.
So the gremlins have been dispelled, and we go on into the PV phase after a delay of about a month. The survey is due to last 6 year so this hiccup is not a big deal really. We can in fact anticipate some early science results from this phase in a month or so, although they will not be part of the full survey which will start after the PV phase is complete, after a few months.
Today I attended a cosmology discussion group where the paper being considered was by Jean-Luc Lehners and Jerome Quintin and was entitled A small Universe. Here is the abstract:
Many cosmological models assume or imply that the total size of the universe is very large, perhaps even infinite. Here we argue instead that the universe might be comparatively small, in fact not much larger than the currently observed size. A concrete implementation of this idea is provided by the no-boundary proposal, in combination with a plateau-shaped inflationary potential. In this model, opposing effects of the weighting of the wave function and of the criterion of allowability of the geometries conspire to favour small universes. We point out that a small size of the universe also fits well with swampland conjectures, and we comment on the relation with the dark dimension scenario.
arXiv:2309.03272
This paper is based on rather speculative arguments. I don’t have anything against those, but the discussion of this particular case reminded me that the idea that the Universe might be much smaller than we think is one that has come and gone many times during my lifetime. The point is that Einstein’s equations of general relativity are local in that they relate the geometric properties of space-time at specific coordinate position to the energy and momentum at the same position. When we make cosmological models based on these equations we usually assume a great deal of symmetry, i.e. that defined in a certain way the spatial sections which form surfaces of simultaneity have the same curvature everywhere, regardless of spatial position. The standard cosmology takes this curvature to be zero, in fact, so the spatial sections are Euclidean (flat), though the curvature could be positive or negative.
Usually when we assume the universe is flat we also assume that it is infinite, but it is possible in principle that a flat universe could be finite, for example in the case of a cube with opposite faces identified so that it has a sort of toroidal symmetry that has no physical edge. The size of the notional cube defines a topological scale which is independent of Einstein’s equations. That’ just a simple example: the topology does not have to be based on a cube; it could be, for example, a rhombic dodecahedron…
Likewise when we talk about a universe with negative spatial curvature we also assume it to be infinite, but that doesn’t have to be the case either: there are spaces with negative spatial curvature which are finite. A manifestation of this idea that I remember from way back in 1999 was a paper by Neil Cornish and David Spergel entitled A small universe after all?
Observing a small universe from the inside produces many interesting effects like a sort of cosmic hall of mirrors. For instance, if you can see far enough you will see the back of your own head. More realistically, the observed large-scale structure of the universe would repeat, and there would be correlated features in the cosmic microwave background. The idea is therefore amenable to observational test; the absence of any of the predicted correlations places constrains the topological scale to be comparable to the size of the observable universe or larger. Of course if it’s infinitely large then the small universe is not small at all…
(For a bit of gratuitous self-promotion, I refer you to a paper I wrote with Graca Rocha and Patrick Dineen back in 2004 using the WMAP observations of the CMB to constrain compact topologies. Given the wealth of new data we have acquired since then I’m sure the constraints are even stronger now.)
Anyway, my point is that speculative ideas are all very well but they don’t mean much if you can’t test them. This one at least has the virtue of making testable predictions.
