Dark matter, the elusive, invisible matter that astronomers say makes up about 85% of the mass of the universe, does not interact with light. Scientists only suspect it’s there because of the way things we can see interact with it. But now, a team in China says it has found the most direct evidence of dark matter yet. According to a study recently published in Physical Review Letters, astrophysicists at the Chinese Academy of Sciences found a “sharp” gamma-ray signal among 15.5 years of data from the Fermi Gamma-ray Space Telescope (FGST). The signal, the paper maintains, is observable support for the mainstream dark matter theory, which posits that dark matter is composed of weakly interacting massive particles (WIMPs). This gamma ray signal is what you would expect to see when those particles collide and annihilate each other. “Discovering a sharp line of gamma rays would be definitive proof of the existence of dark matter particles and would reveal their properties in particle physics,” Yi-Zhong Fan, the study’s first author, told New Scientist. Gamma rays are among the most powerful types of radiation in nature and a key area of interest in the search for dark matter, especially for scientists who support the WIMP theory. According to their name, WIMPs interact too weakly with electromagnetic and nuclear forces to be observable through light or other particle interactions with normal matter. On the other hand, collisions between WIMP and WIMP should produce telltale gamma rays. An intense source of gamma rays with unknown origins will naturally lead some scientists to question whether dark matter was responsible. At least the latest study is far from the first to do so. Last year, a team argued that the gamma glow at the center of the Milky Way was dark matter. Then, a month later, another researcher claimed that WIMPs were responsible for another strange gamma-ray signal, also from FGST data. That said, “irrefutable evidence” of gamma rays is not easy to demonstrate. There have been occasions when supposed dark matter signals of this nature were later shown to be just an instrument error. The study also looked at a handful of galaxy clusters, so it’s always possible that this particular cluster was an anomaly. However, the team argued in the paper that their calculations considering signal-to-noise ratios “disfavor an instrumental origin.” Either way, it seems worth investigating the physical origin of the signal, given its significantly sharp and clear nature, the researchers added in the study. It’s also worth noting that, once again, it’s not just this equipment that records some truly inexplicable gamma ray signals. The FGST is still active and will have doubled its data set by 2040. International space agencies are also preparing to launch new gamma-ray telescopes in the coming years, so who knows? Perhaps gamma rays really will end up being humanity’s first contact with dark matter.
