Comprehensive emissions modeling by global physicists restricts particle candidates.
The detection of an excess of high-energy radiation in the center of the Fermi gamma-ray space telescope more than a decade ago Milky Way convinced some physicists that they saw evidence of dark matter particle annihilation, but a team led by researchers at the University of California, Irvine, has ruled out that interpretation.
In a recent article in the magazine Physical examination D.UCI scientists and colleagues at Virginia Polytechnic Institute and State University, as well as other institutions, report that through analysis of the Fermi data and an extensive series of modeling exercises, they found that the gamma rays observed could not be generated by what is considered weak interacting massive particles is most commonly theorized as dark matter.
By eliminating these particles, the destruction of which could generate energies of up to 300 giga-electron volts, the authors of the paper have imposed the greatest restrictions on the properties of dark matter to date.
The interpretation of the Milky Way by an artist shows the “box-shaped” distribution of the stars in the Galactic Center. A team of physicists led by the UCI said in a recently published study that this shape leaves very little room for excess radiation from the destruction of dark matter particles. Photo credit: Oscar Macias for UCI
“For about 40 years the prime candidate for dark matter among particle physicists has been a thermal, weakly interacting, and weakly scaled particle, and this result for the first time precludes this candidate from passing into very massive particles,” said co-author Kevork Abazajian, UCI professor of physics and astronomy.
“In many models, this particle ranges from 10 to 1000 times the mass of a proton, with more massive particles theoretically being less attractive than dark matter particles,” added co-author Manoj Kaplinghat, also UCI professor of physics and astronomy. “In this article, we are eliminating candidates for dark matter over the preferred range, which is a huge improvement on the constraints we place on the ability to be representative of dark matter.”
Abazajian said dark matter signals could be displaced by other astrophysical phenomena in the Galactic Center – such as star formation, deflection of cosmic rays from molecular gas, and particularly neutron stars and millisecond pulsars – as sources of excess gamma rays emitted by the Fermi space telescope.
This representation of data from the Fermi gamma-ray space telescope after its launch in 2008 shows an excess of high-energy radiation in the galactic center of the Milky Way. Many physicists attributed this to the annihilation of weakly interacting dark matter particles, but a UCI-led study ruled out this possibility due to a range of particle masses. Photo credit: Oscar Macias for UCI
“We looked at all of the different models taking place at 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 the UCI in 2017 initiated this project. “It took us over three years to bring all of these new, better models together and study the emissions. We found out that there is only little space left for dark matter. ”
Macias, who is also a postdoctoral fellow at the GRAPPA center at the University of Amsterdam, added that this result would not have been possible without data and software from the Fermi Large Area Telescope collaboration.
The group tested all of the model classes used in the Galactic Center region for excess emissions analyzes and their conclusions remained unchanged. “You’d have to create a diffuse emissions model that leaves a big ‘hole’ in them to ease our constraints, and science doesn’t work that way,” Macias said.
Kaplinghat noted that physicists have predicted that the radiation from the annihilation of dark matter would be represented in a neat spherical or elliptical shape emanating from the Galactic Center, but the excess gamma-ray detected by the Fermi Space Telescope after its June 2008 deployment shows up as triaxial . bar-like structure.
“If you look into the Galactic Center, you can see that the stars are spread out in a box,” he said. “There’s a star disk and right in the middle there’s a bulge that’s about 10 degrees in the sky, and it’s actually a very specific shape – a kind of asymmetrical box – and that shape leaves very little room for additional dark matter. ”
Does this research rule out the existence of dark matter in the galaxy? “No,” said Kaplinghat. “Our study limits the types of particles that dark matter could be. The abundant evidence of dark matter in the galaxy is robust and unaffected by our work. ”
Far from seeing the team’s results as daunting, Abazajian said they should encourage physicists to focus on non-popular concepts.
“There are many alternative candidates for dark matter,” he said. “The search will be more like a fishing expedition where you don’t yet know where the fish are.”
Reference: “Strong Limitations of Dark Matter Thermal Relics from Fermi-LAT Observations of the Galactic Center” by Kevork N. Abazajian, Shunsaku Horiuchi, Manoj Kaplinghat, Ryan E. Keeley and Oscar Macias, August 20, 2020, Physical examination D..
DOI: 10.1103 / PhysRevD.102.043012
This research project, which was supported by the National Science Foundation, the US Department of Energy and Japan’s initiative of the World Premier International Research Center, also contributed Ryan Keeley, who received his PhD. in Physics and Astronomy from UCI in 2018 and is now at the Korea Astronomy and Space Science Institute and Shunsaku Horiuchi, a former UCI Postdoctoral Fellow in Physics and Astronomy who is now Assistant Professor of Physics at Virginia Tech.
