The latest analysis of the universe’s gamma-ray background has revealed two different source classes but no evidence of dark matter particles.
Gamma rays are the highest-energy light particles in the cosmos. Most gamma ray particles are produced by supermassive black holes, or blazars. Some particles are emitted by pulsars and supernovae.
Since 2008, the Large Area Telescope mounted on NASA’s Fermi satellite has been mapping the gamma-ray universe. Most of the gamma rays it observes originate inside the Milky Way, but the observatory has also identified more than 3,000 extragalactic sources. However, these sources account for only 25 percent of the gamma rays measured by the Fermi.
The remaining 75 percent make up a diffuse background of gamma rays — the gamma-ray background. As part of the latest analysis effort, researchers attempted to explain the origins of the gamma-ray background by measuring its fluctuations.
The analysis — conducted by astrophysicists at the University of Amsterdam and detailed in the journal Physical Review D — revealed two main source types, a high-energy class and low-energy class.
Astronomers believe unidentified blazars explain the high-energy fluctuations, but can’t yet explain the source or sources of low-energy fluctuations. However, the findings confirm an absence of evidence for dark matter particles among the gamma-ray background.
“Our measurement complements other search campaigns that used gamma rays to look for dark matter and it confirms that there is little room left for dark matter induced gamma-ray emission in the isotropic gamma-ray background,” Mattia Fornasa, an astroparticle physicist, said in a news release.
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