Archive for Dark Energy Spectroscopic Instrument

The Largest Map of the Universe

Posted in The Universe and Stuff with tags , , , on January 14, 2022 by telescoper

Now I’m going to have to update the bit of my popular talks (e.g this one) about `Mapping the Universe’!

After just seven months of operations of the Dark Energy Spectroscopic Instrument (DESI) we now have the largest galaxy redshift survey – and it’s only about 10% of the way through its 5-year programme. Currently mapping the positions of about 7.5 million galaxies, the map will contain over 35 million by the time the survey is complete. Even now it is larger than all previous spectroscopic galaxy redshift surveys put together. The speed of DESI is accounted for by its use of 5000 robotically-positioned fibre-optic cables that can generate spectra of thousands of galaxy from a single pointing of the 4-m telescope on which it is mounted.

You can read more about the latest results from DESI here. I’ll just whet your appetite with this groovy animated picture:

DESI’s three-dimensional “CT scan” of the Universe. We are at in the lower left, looking out over 5 billion light years in the direction of the constellation Virgo. As the video progresses, the perspective sweeps toward the constellation Bootes. Each colored point represents a galaxy; gravity has pulled the galaxies into a “cosmic web” of dense clusters, filaments and voids. (Credit: D. Schlegel/Berkeley Lab using data from DESI)

The twinkling effect arises from the fact that you are viewing different thin slices through the 3D distribution. The dark sections that appear and disappear from time to time are just bits not yet included in the survey.

For those of you not familiar with astronomical distance measurements, 1500 megaparsecs = 1.5 Gigaparsecs = 4.5 billion light years (approximately), so this map is not only mapping the spatial distribution of galaxies but also how this distribution has evolved with cosmic time over billions of years.

First Light at the Dark Energy Spectroscopic Instrument

Posted in The Universe and Stuff with tags , , , , , , on November 4, 2019 by telescoper

While I was away last week there was quite a lot of press coverage (e.g. here) about the new Dark Energy Spectroscopic Instrument, which has just seen first light. I didn’t have time to mention this until now, and in any case  I have little to add to the coverage that has already appeared, but it does give me the excuse to post this nice video – which features quite a few people I actually know! – to describe  the huge galaxy survey that DESI will perform. It’s hard to believe that when I started in the field in 1985 the largest such survey, which took several years to compile, had only a few thousand galaxies in it. The DESI instrument will be able to determine spectra of more sources than that in a single pointing of the telescope that lasts about 20 minutes. Overall it should determine redshifts of over 35 million galaxies! Vorsprung durch Technik.