Weakly interacting massive particles – WIMPs, one of the candidate hypotheses to explain dark matter – are so hard to find on Earth that nobody's ever seen them. However, a just-released analysis of years of gamma ray data suggests they're at the centre of the Milky Way in enormous numbers.
The zone they're talking about is huge: in this paper published at Arxiv and submitted to Physical Review D, the researchers find that there's a sphere with a radius of 5,000 light-years in the centre of the galaxy that's emitting more gamma radiation than expected.
In the analysis, based on publicly-available data from NASA's Fermi gamma ray space telescope, the researchers say the gamma rays can't be accounted for using by any currently-known sources. Their hypothesis is that the radiation is “consistent with the emission expected from annihilating dark matter”.
The research suggests after sources like undiscovered pulsars or cosmic rays colliding with gas clouds are eliminated from the data, the remaining energy – in the 1 to 3 GeV range – could be explained by WIMPs with mass between 31 and 40 GeV annihilating in the hugely energetic region they inhabit.
With known sources removed from the galactic map, the remaining noise might be
WIMPs wiping each other out. Image T Linden, University of Chicago
As one of the lead authors of the paper, Fermilab astrophysicist Dan Hooper told New Scientist, “At this point, there are no known or proposed astrophysical mechanisms or sources that can account for this emission”.
At this point, however, the signal falls far short of being a discovery: there's still a one-in-twelve chance that the signal is a fluctuation in the gamma ray background.
The team included scientists from Harvard, Harvard-Smithsonian, MIT, Fermilab, Princeton and the University of Chicago. ®