An unusual gamma-ray signal could be the most direct evidence of dark matter yet. However, the signal could also be the result of a telescope anomaly or produced by something even stranger than dark matter. Dark matter forms the bones of much of our universe, driving how galaxies cluster, for example.
It also far outweighs all the visible matter, yet for decades researchers have puzzled over what exactly it is. Part of the problem is that they cannot currently observe dark matter directly. Instead, they can only register its effect on its surroundings.
A more direct line of investigation would be to detect particles produced when dark matter collides and annihilates with itself, which some theories suggest ought to happen. Now, Yun-Feng Liang at Guangxi University in China and his colleagues identified a gamma-ray signal that may be the result of this process. Hints of exotic dark matter particles could be hiding in LHC data They found the signal after analysing 15.5 years of data from the Fermi Gamma-ray Space Telescope (FGST), looking at the Virgo, Fornax, and Ophiuchus galaxy clusters specifically.
The researchers chose these galaxy clusters because they are known to contain large halos of dark matter, says Liang. The gamma-ray signal the team found there was shaped like a spike or a line, analogous to a burst of light of only one colour, which some theories predict is the result of dark matter annihilating itself. Based on their statistical analysis of the data, the researchers estimated that there is less than a 1-in-10,000 chance that this signal is random cosmic noise or a purely coincidental pattern.
Yet, several questions remain before the team can declare a definitive discovery. Detecting dark-matter signatures in gamma rays has historically been difficult because the signals tend to be weak and can be confused with telescope errors. One promising gamma-ray signal from 2012, for example, proved to be exactly that.
Zhao-Qiang Shen, also at the Chinese Academy of Sciences, who worked on the new study, says the team members performed a large number of tests to confirm the veracity of their signal, but some possibility of instrument error remains. We can use ordinary sugar in the search for dark matter Moreover, while the new signal is clear when looking at the three galaxy clusters, it seems to vanish closer to the centre of our galaxy, where dark matter is dense, so it should also be annihilating itself and creating gamma rays. He says that looking at only one galaxy cluster instead of all three together increases the chances that the signal is a product of noise or a random pattern.
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