To test those models, the researchers first developed computer simulations of dark matter and its effects on the formation of relatively tiny galaxies inside denser patches of dark matter found circling larger galaxies.

"The faintest galaxies are among the most valuable tools we have to learn about dark matter because they are sensitive to several of its fundamental properties all at once," said Ethan Nadler, the studys lead author and graduate student at Stanford University and SLAC. For instance, if dark matter moves a bit too fast or has gained a little too much energy through long-ago interactions with normal matter, those galaxies wont form in the first place. The same goes for fuzzy dark matter, which if stretched out enough will wipe out nascent galaxies with quantum fluctuations.

By comparing such models with a catalogue of faint dwarf galaxies from the Dark Energy Survey and the Panoramic Survey Telescope and Rapid Response System, or Pan-STARRS, the researchers were able to put new limits on the likelihood of such events. In fact, those limits are strong enough that they start to constrain the same dark matter possibilities direct-detection experiments are now probing and with a new stream of data from the Rubin Observatory Legacy Survey of Space and Time expected in the next few years, the limits will only get tighter.

"Its exciting to see the dark matter problem attacked from so many different experimental angles," said Fermilab and University of Chicago scientist Alex Drlica-Wagner, a Dark Energy Survey collaborator and one of the lead authors on the paper. This is a milestone measurement for DES, and Im very hopeful that future cosmological surveys will help us get to the bottom of what dark matter is.

Still, said Nadler, theres a lot of theoretical work to do. For one thing, there are a number of dark matter models, including a proposed form that can strongly interact with itself, where researchers arent sure of the consequences for galaxy formation. There are other astronomical systems as well, such as streams of stars that might reveal new details when they collide with dark matter.

The research was a collaborative effort within theDark Energy Survey. The research was supported by a National Science Foundation Graduate Fellowship, by the Department of Energy's Office of Science through SLAC, and by Stanford University.

Editors note: this article is based on a press release from Fermilab.

Citation: Ethan Nadler et al., available as an arXiv preprint (http://arxiv.org/abs/2008.00022)

For questions or comments, contact the SLAC Office of Communications atcommunications@slac.stanford.edu.

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Dark Energy Survey census of the smallest galaxies hones the search for dark matter - Stanford University News