Two numerical simulations that compare the distribution of dark matter around a galaxy like our Milky Way. The left panel assumes that particles of dark matter move rapidly in the early universe (warm dark matter), while the right panel assumes that dark matter particles move slowly (cold dark matter). The hot dark matter model provides much less small clumps of dark matter around our Galaxy, and thus far fewer satellite galaxies inhabiting these small clumps of dark matter. By measuring the number of satellite galaxies, scientists can distinguish between these models of dark matter. (Images by Bullock & Boylan-Kolchin, annual review of Astronomy and Astrophysics 2017, based on simulations by V. Robles, T. Kelley, and B. Bozek)
Observations of dwarf galaxies round the Milky Way have simultaneously imposed limitations on three popular theories of dark matter.
A team of scientists led by cosmologists from the Department of Energy’s SLAC and Fermi-National Accelerator Laboratories has placed some of the strictest restrictions to date on the nature of dark matter, drawing on a collection of several dozen small, bright satellite galaxies orbiting the Milky Way to determine what types of dark matter could have led to the population of galaxies we see today.
The new study is important not only for how tightly it can contain dark matter, but also for what it can force, said Risa Wechsler, director of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) at SLAC and Stanford University. “One of the things I find really exciting is that we are able to try three of the most popular theories about dark matter, all at the same time,” she said.
Dark matter makes up 85 percent of matter in the universe and interacts very poorly with ordinary matter except by gravity. Its influence can be seen in the shapes of galaxies and in the large-scale structure of the universe, and yet no one is sure what dark matter is. In the new study, researchers focused on three broad possibilities for the nature of dark matter: relatively fast-moving as well as ‘warm’ dark matter; another form of dark matter “interaction” that originates protons enough to heat up in the early universe, with consequences for galaxy formation; and a third, extremely light particle, known as “fuzzy dark matter”, which extends through quantum mechanics effectively over thousands of light years.
To test these models, the researchers first developed computer simulations of dark matter and its effects on the formation of relatively thin galaxies within darker patches of dark matter found around larger galaxies.
“The weakest galaxies are one of the most valuable tools we need to learn about dark matter because they are simultaneously sensitive to several of their fundamental properties,” said Ethan Nadler, lead author and graduate student at Stanford University. and SLAC. For example, if dark matter moves a little too fast or has gained a little too much energy through interactions with normal matter long ago, these galaxies will not form in the first place. The same goes for fuzzy dark matter, which when stretched out will wipe out new galaxies with quantum fluctuations.
By comparing such models with a catalog of light dwarf galaxies from the Dark Energy Survey and the Panoramic Survey Telescope and Rapid Response System, such as Pan-STARRS, the researchers were able to set new limits for the chance of such events. Indeed, those boundaries are strong enough that they begin with the same possibilities for dark matter limiting experiments for direct detection attempt now – and with a new stream of data from the Rubin Observatory Legacy Survey of space and time expected in the coming years, the boundaries will only get tighter.
“It’s exciting to see that the dark matter problem has been attacked from so many different experimental angles,” Fermilab said. University of Chicago scientist Alex Drlica-Wagner, an associate of Dark Energy Survey and one of the lead authors on the paper. “This is a milestone for DES, and I very much hope that future cosmological research will help us to understand what dark matter is.”
Still, Nadler said, “there is a lot of theoretical work to be done.” For one thing, there are a number of dark matter models, including a proposed form that can interact strongly with itself, where researchers are unsure of the implications for galaxy formation. There are also other astronomical systems, such as streams of stars that may reveal new details as they collide with dark matter.
References: “Milky Way Satellite Census. III. Restrictions on dark matter properties from observations of galaxy status galaxies ”by EO Nadler, A. Drlica-Wagner, K. Bechtol, S. Mau, RH Wechsler, V. Gluscevic, K. Boddy, AB Pace, TS Li, M . McNanna, AH Riley, J. García-Bellido, Y.-Y. Mao, G. Green, DL Burke, A. Peter, B. Jain, TMC Abbott, M. Aguena, S. Allam, J. Annis, S. Avila, D. Brooks, M. Carrasco Kind, J. Carretero, M Costanzi, LN da Costa, J. De Vicente, S. Desai, HT Diehl, P. Doel, S. Everett, AE Evrard, B. Flaugher, J. Frieman, DW Gerdes, D. Gruen, RA Gruendl, J. Gschwend , G. Gutierrez, SR Hinton, K. Honscheid, D. Huterer, DJ James, E. Krause, K. Kuehn, N. Kuropatkin, O. Lahav, MAG Maia, JL Marshall, F. Menanteau, R. Miquel, A Palmese, F. Paz-Chinchón, AA Plazas, AK Romer, E. Sanchez, V. Scarpine, S. Serrano, I. Sevilla-Noarbe, M. Smith, M. Soares-Santos, E. Suchyta, MEC Swanson, G. Tarle, DL Tucker, AR Walker, W. Wester (DES Collaboration), July 31, 2020, Astrophysics> Cosmology and Non-Galactic Astrophysics.
arXiv: 2008.00022
The research was a collaborative effort within the Dark 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.
