Observations of dwarf galaxies around Milky way has provided simultaneous 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 toughest restrictions yet on the nature of dark matter, drawing on a collection of dozens of small, faint satellite galaxies orbiting the Milky Way to determine what kind of dark matter could have led to the population of galaxies we see today.
The new study is important not only for how closely it can limit dark matter, but also for what it can limit, said Risa Wechsler, director of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) at SLAC and Stanford University. “One of the things that I think is really exciting is that we are actually able to start researching 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 weakly with ordinary matter except through gravity. Its influence can be seen in the forms of galaxies and in the large-scale structure of the universe, 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 or “warm” dark matter; another form of “interacting” dark matter that encounters protons enough to have been heated in the early universe, with consequences for the formation of the galaxy; and a third extremely light particle, known as “cloudy dark matter”, which through quantum mechanics effectively extends 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 small galaxies inside denser patches of dark matter found circulating larger galaxies.
“The weakest galaxies are among the most valuable tools we have for learning about dark matter because they are sensitive to several of its basic properties at once,” said Ethan Nadler, lead author and graduate student at Stanford University and SLAC. For example, if dark matter is moving a little too fast or has gained a little too much energy over a long time since interactions with normal matter, these galaxies do not form in the first place. The same is true of cloudy dark matter, which, if stretched out enough, will wipe out future galaxies with quantum fluctuations.
By comparing such models with a catalog of faint dwarf galaxies from the Dark Energy Survey and Panoramic Survey Telescope and Rapid Response System or Pan-STARRS, the researchers were able to set new limits on the probability of such events. In fact, these boundaries are strong enough to begin to limit the same possibilities for dark matter that direct-detection experiments are now exploring – and with a new stream of data from the Rubin Observatory Legacy Survey of Space and Time expected in the next few years, the boundaries only gets tighter.
“It’s exciting to see the dark matter problem attacked from so many different experimental angles,” Fermilab said. University of Chicago scientist Alex Drlica-Wagner, a collaborator of the 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 studies will help us get to the bottom of what dark matter is.”
Still, Nadler said, “there is a lot of theoretical work to be done.” First, there are a number of models of dark matter, including a proposed form that can interact strongly with itself, where scientists are unsure of the consequences of galaxy formation. There are also other astronomical systems, such as streams of stars, that may reveal new details as they collide with dark matter.
Reference: “Milky Way Satellite Census. III. Limitations on dark matter properties from observations of Milky Way satellite 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), 31 July 2020, Astrophysics> Cosmology and non-galactic astrophysics.
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 via SLAC, and by Stanford University.