Dark Energy Spectroscopic Instrument

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Weekly Update from the Open Journal of Astrophysics – 28/02/2026

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags arXiv:2505.02928v3, arXiv:2507.03218v2, arXiv:2507.12784v2, arXiv:2509.01690v2, arXiv:2510.06347v2, arXiv:2512.01082v2, arXiv:2602.17957v1, arXiv:2602.19227v1, arXiv:2602.20101v2, Astrophysics of Galaxies, Bayesian Inference, Dark Energy Science Collaboration, Dark Energy Spectroscopic Instrument, DESI, Diamond Open Access, Diamond Open Access Publishing, Early-Type Galaxies, feedback, Galaxy Dynamics, galaxy formation, galaxy haloes, Galaxy Morphology, HelioSpectroton 5000, High redshift galaxies, Imaging Surveys, Instrumentation and Methods for Astrophysics, ionized gas, LSST, Machine Learning, MEGATRON, Open Access, Open Access Publishing., Open Journal of Astrophysics, RAIL (Redshift Assessment Infrastructure Layers), Solar and Stellar Astrophysics, spectral lines, Ursa Major III, Vera C Rubin Observatory, white dwarfs on February 28, 2026 by telescoper

It’s Saturday once more, so it’s time for another update of activity at the Open Journal of Astrophysics. It has been a busy week. Since the last update we have published a further nine papers, bringing the number in Volume 9 (2026) to 45 and the total so far published by OJAp up to 493.

I will continue to include the posts made on our Mastodon account (on Fediscience) to encourage you to visit it. Mastodon is a really excellent service, and a more than adequate replacement for X/Twitter (which nobody should be using); these announcements also show the DOI for each paper.

The first four papers this week were all published on Monday 23rd February.

The first paper to report is “A Bayesian Exploration of The Mass of the Ursa Major III: Kinematics, Rotation and their influence on the Mass to Light Ratio” by Tim R. Adams (U. Sydney, Australia), Brendon J. Brewer (U. Auckland, New Zealand) and Geraint F. Lewis (Sydney). This paper, in the folder Astrophysics of Galaxies, describes an investigation of the kinematics of potential ultra-faint dwarf galaxy UMa III/U1, finding a preference for a non-rotating model; the object’s nature remains uncertain.

The overlay is here:

You can find the officially accepted version on arXiv here and the announcement on Fediverse here:

The second paper is “The Impact of Baryonic Effects on the Dynamical Masses Inferred Using Satellite Kinematics” by Josephine F.W. Baggen, Frank C. van den Bosch, and Kaustav Mitra (Yale U., USA). This paper, also in the folder Astrophysics of Galaxies, presents a model to assess the impact of stars and gas on satellite kinematics, showing that these baryonic effects can reduce the satellite velocity dispersion and increase inferred central galaxy masses.

The overlay for this one is here:

The official version of the paper can be found on arXiv here and the Fediverse announcement here:

The third paper this week, and the third published on Monday 23rd February, and the third in the folder Astrophysics of Galaxies, is “MEGATRON: Disentangling Physical Processes and Observational Bias in the Multi-Phase ISM of High-Redshift Galaxies” by Nicholas Choustikov (U. Oxford, UK) and 12 others based in UK, USA, France, Korea and Belgium. The study uses MEGATRON simulations to analyze the interstellar medium (ISM) of high-redshift galaxies, finding it denser and less metal-enriched than local galaxies with implications for line ratios as diagnostics

The overlay is here:

The official version can be found on arXiv here and the Fediverse announcement is here:

The fourth paper this week, also published on Monday 23rd February, but in the folder Instrumentation and Methods for Astrophysics, is “Redshift Assessment Infrastructure Layers (RAIL): Rubin-era photometric redshift stress-testing and at-scale production” by the RAIL Team (31 authors) and the Dark Energy Science Collaboration. The article introduces Redshift Assessment Infrastructure Layers (RAIL), an open-source Python library for large-scale probabilistic photo-z estimation, useful for extragalactic research and not limited to LSST data.

Here is the overlay:

The official version can be found on arXiv here and the Fediverse announcement is here:

Moving on to Tuesday 24th February, the fifth paper this week, is “Feedback shaped the galaxy morphological sequence in presence of mergers” by Masafumi Noguchi (Tohoku University, Japan). This article was published in the folder Astrophysics of Galaxies. This study suggests that galaxy morphology, specifically the mass ratios of bulges and disks, is influenced by galaxy mergers and feedback processes from active galactic nuclei and supernovae.

The overlay is here:

The accepted version can be found on arXiv here, and the fediverse announcement is here:

The sixth paper this week is “HelioSpectrotron 5000: an interactive solar atlas” by Alexander G.M. Pietrow (AIP Potsdam, Germany). This was published on Tuesday 24th February in the folder Solar and Stellar Astrophysics. This describes HelioSpectrotron~5000 (HS5000), which is an interactive solar spectral atlas that allows comparison between high-resolution spectra and ground-based instrument observations, aiding in wavelength calibration and line identification. The software can be found here; I had a play with it yesterday and it’s very easy to use!

The overlay is here:

You can find the officially accepted version on arXiv here and the Mastodon announcement is here:

The seventh paper of this week was published on Thursday 26th February is “The Rise of Ionized Gas Filaments in Early-Type Galaxies” by Ryan Eskenasy (U. Kentucky, USA), Valeria Olivares (Universidad de Santiago de Chile) and Yuanyuan Su (U. Kentucky, USA). This article, in the folder Astrophysics of Galaxies, is an exploration of the formation of multiphase filamentary nebulae in early-type galaxies (ETGs), using VLT-MUSE IFU observations of 126 non-central ETGs, focussing on the hot gas components thereof.

The overlay is here:

The officially accepted version of this paper can be found on the arXiv here and the Mastodon announcement is here:

Number eight for this week is “Relationship Between Major Stellar Physical Parameters and Normal Mode Frequencies in Accreting White Dwarf Stars” by Praphull Kumar, Dean M. Townsley and Hunter Anz (U. Alabama, USA). This was published on Thursday 26th February in the category Solar and Stellar Astrophysics; the paper presents a new method for identifying pulsation modes in white dwarfs, improving upon previous models by using more realistic parameters and considering thermohaline mixing and element diffusion. The overlay is here:

The final version of this paper can be found on the arXiv here and the Mastodon announcement is here:

The ninth, and final, paper for this week is “A Semi-Supervised Learning Method for the Identification of Bad Exposures in Large Imaging Surveys” by Yufeng Luo (U. Wyoming, USA) and 8 others from the DESI Legacy Imaging Surveys Team. This was published on Friday 27th February, i.e yesterday, in the folder Instrumentation and Methods for Astrophysics. The paper describes a machine-learning approach for detecting poor-quality exposures in large astronomical imaging surveys, proving efficient and accurate in identifying problematic exposures.

The overlay is here:

The official version on arXiv can be found here and the Mastodon announcement follows:

And that concludes this week’s update. We have now published 45 papers in two complete months of 2026, on which basis we can estimate about 270 papers in the year. For the record, in the first two months of 2025 we published 21 papers.

P.S. Thank you to the many people who responded to the latest call for editors. I’ve been sending out invitations and getting people onboard as quickly as I can, but I still have a number to get to so please bear with me!

1 Comment »

Dark Energy Survey Year Y6 Results Day!

Posted in The Universe and Stuff with tags Cosmology, Dark Energy, Dark Energy Spectroscopic Instrument, Dark Energy Survey, DES, DES Year 6, DESI on January 22, 2026 by telescoper

This morning’s arXiv announcement contained a number of papers related to the Dark Energy Survey Y6 analysis. There is also a Zoom webinar later today at 10.30 Central Time (16.30 GMT; 13.30 in Greenland). Details can be found here.

You can find links to and abstracts of all the papers here, but I thought it would be useful to provide arXiv links to the latest batch here.

arXiv:2601.14559 Dark Energy Survey Year 6 Results: Cosmological Constraints from Galaxy Clustering and Weak Lensing – this is the key summary paper.
arXiv:2601.14484 Dark Energy Survey Year 6 Results: MagLim++ Lens Sample Selection and Measurements of Galaxy Clustering
arXiv:2601.14864 Dark Energy Survey: DESI-Independent Angular BAO Measurement
arXiv:2601.15175 Dark Energy Survey Year 6 Results: Galaxy-galaxy lensing
arXiv:2601.14833 Dark Energy Survey Year 6 Results: Magnification modeling and its impact on galaxy clustering and galaxy-galaxy lensing cosmology
arXiv:2601.14859 Dark Energy Survey Year 6 Results: Weak Lensing and Galaxy Clustering Cosmological Analysis Framework

A number of DES Y6 papers already published – including several in the Open Journal of Astrophysics – are listed here.

I’ll just highlight a couple of points from the first paper listed above, which uses the now standard “3x2pt” analysis, which combines three complementary two-point correlation functions: cosmic shear; galaxy-galaxy lensing and galaxy clustering. The abstract of this paper is as follows:

A notable result is contained in the last sentence. The simplest interpretation of dark energy is that it is a cosmological constant (usually called Λ) which – as explained here – corresponds to a perfect fluid with an equation-of-state p=wρc² with w=-1. In this case the effective mass density ρ of the dark energy remains constant as the universe expands. To parametrise departures from this constant behaviour, cosmologists have replaced this form with the form w(a)=w₀+w_a(1-a) where a(t) is the cosmic scale factor. A cosmological constant Λ would correspond to a point (w₀=-1, w_a=0) in the plane defined by these parameters, but the only requirement for dark energy to result in cosmic acceleration is that w<-1/3, not that w=-1. Results last year from DESI suggested values of w₀ ≠-1 and w_a≠0 , but the current DES results are consistent with w=-1; they do not constrain w₀ and w_a jointly.

For reference on the left you can find the (w₀, w_a) plane from DESI.

I thought I’d add one of the other cosmological contraint plots:

The results look qualitatively similar to previous plots but the contours have shifted a bit.

2 Comments »

Weekly Update from the Open Journal of Astrophysics – 25/10/2025

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags ACT, arXiv:2502.17674v2, arXiv:2502.17675v2, arXiv:2502.17676v2, arXiv:2502.17677v2, arXiv:2508.20904v2, Atacama Cosmology Telescope, cosmic shear, Cosmology, Cosmology and NonGalactic Astrophysics, Dark Energy Spectroscopic Instrument, DECADE cosmic shear project, DESI, Diamond Open Access, Diamond Open Access Publishing, galaxy clustering, Open Access, Open Journal of Astrophysics, The Open Journal of Astrophysics, thermal Sunyaev-Zeldovich effect, weak gravitational lensing on October 25, 2025 by telescoper

It may be a Bank Holiday weekend here in Ireland, but it’s still time for the usual Saturday update of the week’s new papers at the Open Journal of Astrophysics (although a bit later in the day than usual). Since the last update we have published another five papers, which brings the number in Volume 8 (2025) up to 161, and the total so far published by OJAp up to 396.

This week’s update is rather unusual because there are four papers in a series (or, more precisely, mathematically speaking, a sequence) all published on the same day (Wednesday October 22nd 2025), in the same folder (Cosmology and NonGalactic Astrophysics), with the same first author (Dhayaa Anbajagane of the University of Chicago), with long author lists and many co-authors in common. These papers all relate to the DECADE cosmic shear project. Instead of doing them one by one, therefore, I’ve decided to put all four overlays together and provide links to all the papers afterwards. As I’m trying to encourage people to follow our feed on the Fediverse via Mastodon (where I announce papers as they are published, including the all-important DOI), I’ll include links to each announcement there too.

“The DECADE cosmic shear project I: A new weak lensing shape catalog of 107 million galaxies“, accepted version on arXiv here.
“The DECADE cosmic shear project II: photometric redshift calibration of the source galaxy sample“, accepted version on arXiv here.
“The DECADE cosmic shear project III: validation of analysis pipeline using spatially inhomogeneous data“, accepted version on arXiv here.
“The DECADE cosmic shear project IV: cosmological constraints from 107 million galaxies across 5,400 deg² of the sky“, accepted version on arXiv here.

The fediverse announcements follow:

Open Journal of Astrophysics

@OJ_Astro@fediscience.org

New Publication at the Open Journal of Astrophysics: "The DECADE cosmic shear project I: A new weak lensing shape catalog of 107 million galaxies" by Dhayaa Anbajagane (University of Chicago, USA) et al. (54 authors)

https://doi.org/10.33232/001c.146158

October 22, 2025, 12:42 pm 2 boosts 0 favorites

Open Journal of Astrophysics

@OJ_Astro@fediscience.org

New Publication at the Open Journal of Astrophysics: "The DECADE cosmic shear project II: photometric redshift calibration of the source galaxy sample" by Dhayaa Anbajagane (University of Chicago, USA) et al. (53 authors)

https://doi.org/10.33232/001c.146159

October 22, 2025, 1:07 pm 2 boosts 0 favorites

Open Journal of Astrophysics

@OJ_Astro@fediscience.org

New Publication at the Open Journal of Astrophysics: "The DECADE cosmic shear project III: validation of analysis pipeline using spatially inhomogeneous data" by Dhayaa Anbajagane (University of Chicago, USA) et al. (53 authors)

https://doi.org/10.33232/001c.146160

October 22, 2025, 1:57 pm 1 boosts 0 favorites

Open Journal of Astrophysics

@OJ_Astro@fediscience.org

New Publication at the Open Journal of Astrophysics: "The DECADE cosmic shear project IV: cosmological constraints from 107 million galaxies across 5,400 deg^2 of the sky" by Dhayaa Anbajagane (University of Chicago, USA) et al. (75 authors)

https://doi.org/10.33232/001c.146161

October 22, 2025, 2:47 pm 1 boosts 0 favorites

The fifth and final paper for this week is “Clustering of DESI galaxies split by thermal Sunyaev-Zeldovich effect” by Michael Rashkovetskyi of the Harvard-Smithsonian Center for Astrophysics, or CfA for short, and 48 others. This one was published on Wednesday 23rd October in the folder Cosmology and NonGalactic Astrophysics. This paper explores how the clustering properties of galaxies mapped by the Dark energy Spectroscopic Instrument (DESI) relate to the local thermal Sunyaev-Zeldovich emission mapped by the Atacama Cosmology Telescope (ACT). The overlay is here:

The officially accepted version can be found on arXiv here, and the fediverse announcement is here:

Open Journal of Astrophysics

@OJ_Astro@fediscience.org

New Publication at the Open Journal of Astrophysics: "Clustering of DESI galaxies split by thermal Sunyaev-Zeldovich effect" by Michael Rashkovetskyi (Cfa Harvard-Smithsonian, USA) et al. (49 authors)

https://doi.org/10.33232/001c.146033

October 23, 2025, 8:28 am 1 boosts 0 favorites

That concludes the papers for this week. With one week to go and our total at 396, I still think we might reach the 400 total by the end of October.

1 Comment »

Cosmology Results from DESI

Posted in Astrohype, The Universe and Stuff with tags baryon acoustic oscillations, cosmological constant, Cosmology, Dark Energy, Dark Energy Spectroscopic Instrument, Occam's Razor, Shaun Hotchkiss on March 20, 2025 by telescoper

Yesterday evening (10pm Irish Time) saw the release of new results from the Dark Energy Spectroscopic Instrument (DESI), completing a trio of major announcements of cosmological results in the space of two days (the Atacama Cosmology Telescope and the Euclid Q1 release being the others). I didn’t see the DESI press conference but you can read the press release here.

There were no fewer than eight DESI papers on the astro-ph section of the arXiv this morning. Here are the titles with links:

You can see from the titles that the first seven of these relate to the second data release (DR2; three years of data) from DESI; the last one listed here is a description of the first data release (DR1), which is now publicly available.

Obviously there is a lot of information to digest in these papers so here are two members of the DESI collaboration talking with Shaun Hotchkiss on Cosmology Talks about the key messages from the analysis of Baryon Acoustic Oscillations (the BAO in the titles of the new papers):

A lot has been made in the press coverage of these results about the evidence that the standard cosmological model is incomplete; see, e.g., here. Here are a few comments.

As I see it, taken on their own, the DESI BAO results are broadly consistent with the ΛCDM model as specified by the parameters determined by the Cosmic Microwave Background (CMB) inferred from Planck. Issues do emerge, however, when these results are combined with other data sets. The most intriguing of these arises with the dark energy contribution. The simplest interpretation of dark energy is that it is a cosmological constant (usually called Λ) which – as explained here – corresponds to a perfect fluid with an equation-of-state p=wρc² with w=-1. In this case the effective mass density of the dark energy ρ remains constant as the universe expands. To parametrise departures from this constant behaviour, cosmologists have replaced this form with the form w(a)=w₀+w_a(1-a) where a(t) is the cosmic scale factor. A cosmological constant Λ would correspond to a point (w₀=-1, w_a=0) in the plane defined by these parameters, but the only requirement for dark energy to result in cosmic acceleration is that w<-1/3, not that w=-1.

The DESI team allow (w₀, w_a) to act as free parameters and let the DESI data constrain them, either alone or in combinations with other data sets, finding evidence for departures from the “standard values”. Here’s an example plot:

The DESI data don’t include the standard point (at the intersection of the two dashed lines) but the discrepancy gets worse when other data (such as supernovae and CMB) are folded in, as in this picture. The weight of evidence suggests a dark energy contribution which is decreasing with time.

These results are certainly intriguing, and a lot of credit is due to the DESI collaboration for working so hard to identify and remove possible systematics in the analysis (see the papers above) but what do they tell us about ΛCDM?

My view is that we’ve never known what the dark energy actually is or why it is so large that it represents 70% of the overall energy density of the Universe. The Λ in ΛCDM is really just a place-holder, not there for any compelling physical reason but because it is the simplest way of accounting for the observations. In other words, it’s what it is because of Occam’s Razor and nothing more. As with any working hypothesis, the standard cosmological model will get updated whenever new information comes to light (as it is doing now) and/or if we get new physical insights into the origin of dark energy.

Do the latest observations cast doubt on the standard model? I’d say no. We’re seeing an evolutionary change from “We have no idea what the dark energy is but we think it might be a cosmological constant” to “We still have no idea what the dark energy is but we think it might not be a cosmological constant”.

11 Comments »

Cosmology Talks: Recent DESI Power Spectrum Results

Posted in The Universe and Stuff with tags Cosmology, Cosmology Talks, Dark Energy, Dark Energy Spectroscopic Instrument, DESI, Physics on December 12, 2024 by telescoper

Some weeks ago I posted an item about recent results that have emerged from the DESI (Dark Energy Spectroscopic Instrument) Collaboration. I have been a bit busy since then but I just saw that there is one of those Cosmology Talks about these results which I thought I would pass on. The contributors are Arnaud de Mattia, Hector Gil-Marín and Pauline Zarrouk and they are talking about the analsysis they have done using the “full shape” of the galaxy power spectrum. It’s quite a long video, but very illuminating.

New Results from DESI

Posted in Barcelona, The Universe and Stuff with tags astronomy, Cosmology, Dark Energy, Dark Energy Spectroscopic Instrument, dark matter, DESI, ICCUB, Physics on November 20, 2024 by telescoper

The Mayall Telescope at Kitt Peak, in which DESI is housed. This PR image was taken during a meteor shower, which is not ideal observing conditions. Picture Credit: KPNO/NOIRLab/NSF/AURA/R. Sparks

I’ve just got time between meetings to mention that a clutch of brand new papers has emerged from the DESI (Dark Energy Spectroscopic Instrument) Collaboration. There is a press release discussing the results from the Lawrence Berkeley Laboratory here and one from the ICCUB in Barcelona here; several members of the group I visited there during sabbatical are working on DESI. Congratulations to them.

I haven’t had time to read them yet, but a quick skim suggests that the results are consistent with the standard cosmological model.

The latest batch contains three Key Publications:

DESI Collaboration et al., DESI 2024 II: Sample Definitions, Characteristics, and Two-point Clustering Statistics
DESI Collaboration et al., DESI 2024 V: Full-Shape Galaxy Clustering from Galaxies and Quasars
DESI Collaboration et al., DESI 2024 VII: Cosmological Constraints from the Full-Shape Modeling of Clustering Measurements

together with the companion supporting papers:

Ishak et al. (2024), Modified Gravity Constraints from the Full Shape Modeling of Clustering Measurements from DESI 2024
Rosado-Marín et al. (2024), Mitigating Imaging Systematics for DESI 2024 Emission Line Galaxies and Beyond
Bianchi et al. (2024), Characterization of DESI fiber assignment incompleteness effect on 2-point clustering and mitigation methods for Y1 analysis
Forero-Sánchez et al. (2024), Analytical and EZmock covariance validation for the DESI 2024 results
Findlay et al. (2024), Exploring HOD-dependent systematics for the DESI 2024 Full-Shape galaxy clustering analysis

The links lead to the arXiv version of these papers. These articles can also be found, along with previously released publications by the DESI Collaboration, here.

Anyone who has read the latest papers is welcome to comment through the box below!

3 Comments »

Evolving Dark Energy or Supernovae Systematics?

Posted in The Universe and Stuff with tags Cosmology, Dark Energy, Dark Energy Spectroscopic Instrument, Dark Energy Survey, DES, DESI, evolving dark energy, Pantheon on August 15, 2024 by telescoper

A few months ago I posted an item about the release new results from the Dark Energy Spectroscopic Instrument (DESI). That was then followed by a presentation explaining the details which you can find here to find out more about the techniques involved. At the time the new DESI results garnered a lot of media attention much of it about claims that the measurements provided evidence for “New Physics”, such as evolving dark energy. Note that the DESI results themselves did not imply this. Only when combined with supernova measurements did this suggestion arise.

Now there’s a new preprint out by George Efstathiou of Cambridge. The abstract is here:

Recent results from the Dark Energy Spectroscopic Instrument (DESI) collaboration have been interpreted as evidence for evolving dark energy. However, this interpretation is strongly dependent on which Type Ia supernova (SN) sample is combined with DESI measurements of baryon acoustic oscillations (BAO) and observations of the cosmic microwave background (CMB) radiation. The strength of the evidence for evolving dark energy ranges from ~3.9 sigma for the Dark Energy 5 year (DES5Y) SN sample to ~ 2.5 sigma for the Pantheon+ sample. Here I compare SN common to both the DES5Y and Pantheon+ compilations finding evidence for an offset of ~0.04 mag. between low and high redshifts. Correcting for this offset brings the DES5Y sample into very good agreement with the Planck LCDM cosmology. Given that most of the parameter range favoured by the uncorrected DES5Y sample is discrepant with many other cosmological datasets, I conclude that the evidence for evolving dark energy is most likely a result of systematics in the DES5Y sample.

Here are a couple of figures from the paper illustrating the difference in parameter constraints using the uncorrected (left) and corrected (right) Dark Energy (Survey) 5 year Supernova sample.

The y-axis shows a parameter w_a, which is zero in the standard model with non-evolving dark energy; the non-zero value implied by the left hand panel using the uncorrected data.

Just as with the Hubble Tension I blogged about yesterday, the evidence for a fundamental revision of our standard model may be nothing of the sort but some kind of systematic error. I think we can expect a response from the Dark Energy Survey (DES) team. Grab your popcorn.

1 Comment »

Presentation of the BAO DESI results at ICCUB Uni Barcelona – by Licia Verde & Héctor Gil Marin

Posted in The Universe and Stuff with tags Barcelona, baryon acoustic oscillations, Cosmology, Dark Energy Spectroscopic Instrument, DESI on April 8, 2024 by telescoper

Last week, when I wrote about the new results from the Dark Energy Spectroscopic Instrument (DESI) I mentioned that there would be a seminar here at ICCUB about that very topic. Well, the seminar, by Licia Verde & Héctor Gil Marin, was recorded and here it is:

Cosmology Talks: Cosmological Constraints from BAO

Posted in The Universe and Stuff, YouTube with tags astronomy, Cosmology, Cosmology Talks, Dark Energy, Dark Energy Spectroscopic Instrument, DESI, Physics, Science, Shaun Hotchkiss, Universe on April 5, 2024 by telescoper

Here’s another video in the Cosmology Talks series curated by Shaun Hotchkiss. This one very timely after yesterday’s announcement. Here is the description on the YouTube page:

The Dark Energy Spectroscopic Instrument (DESI) has produced cosmological constraints! And it is living up to its name. Two researchers from DESI, Seshadri Nadathur and Andreu Font-Ribera, tell us about DESI’s measurements of the Baryon Acoustic Oscillations (BAO) released today. These results use one full year of DESI data and are the first cosmological constraints from the telescope that have been released. Mostly, it is what you might expect: tighter constraints. However, in the realm of the equation of state of dark energy, they find, even with BAO alone, that there is a hint of evidence for evolving dark energy. When they combine their data with CMB and Supernovae, who both also find small hints of evolving dark energy on their own, the evidence for dark energy not being a cosmological constant jumps as high as 3.9σ with one combination of the datasets. It seems there still is “concordance cosmology”, it’s just not ΛCDM for these datasets. The fact that all three probes are tentatively favouring this is intriguing, as it makes it unlikely to be due to systematic errors in one measurement pipeline.

My own take is that the results are very interesting but I think we need to know a lot more about possible systematics before jumping to conclusions about time-varying dark energy. Am I getting conservative in my old age? These results from DESI do of course further underline the motivation for Euclid (another Stage IV survey), which may have an even better capability to identify departures from the standard model.

P.S. Here’s a nice graphic showing the cosmic web showing revealed by the DESI survey:

2 Comments »

DESI Year 1 Results: Baryon Acoustic Oscillations

Posted in Barcelona, Euclid, The Universe and Stuff with tags baryon acoustic oscillations, Cosmology, Dark Energy Spectroscopic Instrument, DESI, Hubble Tension on April 4, 2024 by telescoper

There has been a lot of excitement around the ICCUB today – the press have been here and everything – ahead of the release of the Year 1 results from the Dark Energy Spectroscopic Instrument (DESI). The press release from the Lawrence Berkeley Laboratory in California can be found here.

The papers were just released at 5pm CEST and can be found here. The key results pertain to Baryon Acoustic Oscillations (BAOs) which can be used to track the expansion rate and geometry of the Universe. This is one of the techniques that will be used by Euclid.

There’s a lot of technical information to go through and I have to leave fairly soon. Fortunately we have seminar tomorrow that will explain everything at a level I can understand:

I will update this post with a bit more after the talk, but for the time being I direct you to the high-level cosmological implications are discussed in this paper (which is Paper VI from DESI).

If your main interest is in the Hubble Tension then I direct you to this Figure:

Depending on the other data sets included, the value obtained is around 68.5 ± 0.7 in the usual units, closer to the (lower) Planck CMB value than the (higher) Supernovae values but not exactly in agreement; the error bars are quite small too.

You might want to read my thoughts about distances estimated from angular diameters compared with distances measured using luminosity distances here.

If you’re wondering whether there is any evidence for departures from the standard cosmology, another pertinent comment is:

In summary, DESI data, both alone and in combination with other cosmological probes, do not show any evidence for a constant equation of state parameter different from −1 when a flat wCDM model is assumed.
DESI 2024 VI: Cosmological Constraints from the Measurements of Baryon Acoustic Oscillations

More complicated models of time-varying dark energy might work, but there’s no strong evidence from the current data.

That’s all from me for now, but feel free to comment through the box below with any hot takes!

UPDATE: As expected there has been quite a lot of press coverage about this – see the examples below – mostly concentrating on the alleged evidence for “new physics”. Personally I think the old physics is fine!

In the Dark

Archive for Dark Energy Spectroscopic Instrument

Weekly Update from the Open Journal of Astrophysics – 28/02/2026

Open Journal of Astrophysics

Open Journal of Astrophysics

Open Journal of Astrophysics

Open Journal of Astrophysics

Open Journal of Astrophysics

Open Journal of Astrophysics

Open Journal of Astrophysics

Open Journal of Astrophysics

Open Journal of Astrophysics

Dark Energy Survey Year Y6 Results Day!

Weekly Update from the Open Journal of Astrophysics – 25/10/2025

Open Journal of Astrophysics

Open Journal of Astrophysics

Open Journal of Astrophysics

Open Journal of Astrophysics

Open Journal of Astrophysics

Cosmology Results from DESI

Cosmology Talks: Recent DESI Power Spectrum Results

New Results from DESI

Evolving Dark Energy or Supernovae Systematics?

Presentation of the BAO DESI results at ICCUB Uni Barcelona – by Licia Verde & Héctor Gil Marin

Cosmology Talks: Cosmological Constraints from BAO

DESI Year 1 Results: Baryon Acoustic Oscillations

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