In the Dark

Yesterday the Open Journal of Astrophysics published a paper by Porredon et al which will feature in the usual Saturday round-up. That paper, which is based on the First Data Release from the Dark Energy Spectroscopic Instrument (DESI) reminded me that I should mention that DESI recently reached an amazing milestone – it has now mapped the positions and redshifts of 47 million galaxies and quasars! There is a full press-release about this achievement here.

Here’s a little video showing how the survey works:

There are more videos and other graphics in the press release.

Here’s a nice picture showing a thin slice through the full survey that reveals the characteristic “cosmic web” of the large-scale structure of the Universe in all its glory:

This progress is great, but it really makes me feel old. Forty years ago, in 1986, I had just started my PhD. The state-of-the-art galaxy redshift survey slice then is shown in this plot, from de Lapparent et al 1986 (ApJLett 302, L1), one of the first papers I read as a research student (I got it in 1985 as a preprint), which contains just 1,100 galaxies:

It is worth mentioning that although DESI has now covered its original target area, it will continue until 2028. You can never have too many galaxy redshifts!

This entry was posted on April 29, 2026 at 10:14 pm and is filed under Biographical, The Universe and Stuff with tags Cosmic Web, Cosmology, Dark Energy, Dark Energy Spectroscopic Instrument, DESI, Galaxy redshift surveys. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.