Study excludes destruction of dark matter as origin of extra radiation in galaxy

The discovery of an excess of high-energy radiation in the center of the Milky Way by the Fermi Gamma Ray Space Telescope more than ten years ago convinced some physicists that they saw evidence of the destruction of dark matter particles, but a team among led by researchers at the University of California, Irvine has ruled out that interpretation.

In an article recently published in the magazine Physical assessment D, the UCI scientists and colleagues at Virginia Polytechnic Institute and State University and other institutions reported that they – through an analysis of the Fermi data and an extensive series of model exercises – were able to determine that the observed gamma rays could not be produced by so-called weak interaction with massive particles are called, most popularly theorized as the game of dark matter.

By eliminating these particles, the destruction of which can generate up to 300 giga-electron volts, the authors of the paper say, they have set the strongest limits yet for properties of dark matter.

“For 40 years or so, the leading candidate for dark matter among particle physicists has been a thermal, weak interaction and weak scale particle, and this result excludes for the first time that candidate to whole mass particles,” said co-author Kevork Abazajian, UCI professor of physics and astronomy.

“In many models, this particle varies from 10 to 1,000 times the mass of a proton, with more massive particles theoretically less attractive than a particle of dark matter,” added co-author Manoj Kaplinghat, also a UCI professor of physics and astronomy. ta. “In this paper, we eliminate candidates of dark matter over the preferred range, which is a huge improvement in the constraints we place on the possibilities that these are representative of dark matter.”

Abazajian said that dark matter signals may be disturbed by other astrophysical phenomena in the Galactic Center – such as star formation, cosmic radiation deviation of molecular gas and, mostly neutron stars and millisecond pulsars – as sources of redundant gamma rays discovered by the Fermi space.

“We’ve been looking at all the different modeling that is going on in the Galactic Center, including molecular gas, stellar emissions and high-energy electrons that scatter low-energy photons,” said co-author Oscar Macias, a postdoctoral fellow in physics and astronomy. at the Kavli Institute of Physics and Mathematics of the Universe at the University of Tokyo, whose visit to UCI in 2017 began this project. “It took us more than three years to pull all these new, better models together and examine the emissions, finding that there is not much room for dark matter.”

Macias, who is also a postdoctoral researcher at the GRAPPA Center at the University of Amsterdam, added that this result would not be possible without data and software provided by the Fermi Large Area Telescope collaboration.

The group tested all classes of models used in the Galactic Center region for analysis of excess emissions, and their conclusions remained unchanged. “One would have to create a diffuse emission model that leaves a big ‘hole’ in it to relax our constraints, and science does not work that way,” Macias said.

Kaplinghat determined that physicists had predicted that radiation of destruction of dark matter would be represented in a crescent-shaped spherical or elliptical shape emanating from the Galactic Center, but the gamma-ray surplus discovered by the Fermi Space Telescope after the June 2008 deployment appears as a triaxial, bar-like structure.

“If you look at the Galactic Center, you see the stars being distributed in a boxing way,” he said. “There’s a disk of stars, and right in the center there’s a mound that’s about 10 degrees in the sky, and it’s actually a very specific shape – sort of an asymmetrical box – and this form leaves very little room for extra dark matter. “

Does this study rule out the existence of dark matter in the galaxy? “No,” said Kaplinghat. “Our study limits the kind of particle that dark matter can be. The multiple lines of evidence for dark matter in the galaxy are robust and unaffected by our work.”

Far from considering the team’s findings as discouraging, Abazajian said they should encourage physicists to concentrate on concepts other than the most popular.

“There are a lot of alternative candidates for dark matter,” he said. “The search will be more than a fishing expedition where you do not already know where the fish are.”