The largest ever map of the universe captures 47 million galaxies and quasars

A five-year survey of the sky that captured more than 47 million galaxies and quasars has now been completed, allowing researchers to put the finishing touches on the most detailed map of the universe ever made. The data could help solve the mystery of the apparent weakening of dark energywhich threatens to overturn our standard model of the cosmos.

The Dark Energy Spectroscopic Instrument (DESI) at Kitt Peak National Observatory in Arizona has been scanning the sky since 2021. Researchers originally expected its survey to collect data on 34 million galaxies and quasars, but DESI surprised researchers with its efficiency. Because of the vast distances, some of these extremely faint galaxies have been observed by only 100 or 200 photons.

David Schlegel at the Lawrence Berkeley National Laboratory in California says our previous maps of the cosmos include a total of 5 million galaxies, so the DESI data increases our knowledge of the universe by a factor of nearly 10.

“We’ve actually been on that curve now my whole career where every 10 years we’re making 10 times bigger cards,” he says. “You can ask the question at what point have you mapped every observable galaxy within 10 billion light-years … and if we stay on the curve, we’ll do that by 2061.”

The main study has now been completed, but it will take another year to analyze the data before it is made available to researchers. The project will continue to collect data for at least another two and a half years, and Schlegel says there are hopes that DESI can be upgraded and continue to operate well into 2030. “It’s still the leading instrument of its kind in the world,” he says.

The DESI map now covers 14,000 square degrees of the sky, but the team hopes to expand this to 17,000 square degrees. The entire sky is over 41,000 square degrees, but much of this is difficult to observe due to relatively close and bright objects, such as our own galaxy, the Milky Way.

The data will allow scientists to compare how galaxies were distributed in the distant past and today. This could lead to insights into the power of dark energy, which makes up about 70 percent of the universe. An earlier set of data from DESI in 2024 suggests that instead of remaining constant as expected, dark energy is weakening over time.

If dark energy is indeed weakening, this would be the case profound implications for the Standard Model of cosmologyknown as lambda-CDM. The full DESI data set will allow this phenomenon to be investigated further.

I suggest Lahav from University College London says accessing the latest map from DESI would have seemed like science fiction early in his career. “When I was a PhD student at Cambridge, 40 years ago, we had a sample of thousands of galaxies. The community was hungry for data,” he says. “I think my students (today) might have the opposite problem; being inundated with data and it’s very challenging to analyze it.”

With so much data, there will be scientific breakthroughs about the nature of the universe, Lahav says, but we’ve also likely caught unusual one-off cosmological incidents that lead to exciting research.

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