In the early 1930s, Swiss astronomer Fritz Zwicky noticed that galaxies in space were moving too fast to be held together by visible mass. He proposed the existence of some invisible ‘scaffolding’-dark matter. Nearly a century later, data from the Fermi gamma-ray telescope might confirm this hypothesis. Dark matter does not interact with electromagnetic radiation: it doesn’t absorb, reflect, or emit light, making it invisible. Until now, scientists could only study it indirectly through its gravitational effects on visible matter.
Many scientists suggest that dark matter consists of so-called Weakly Interacting Massive Particles (WIMPs). These particles are heavier than protons but interact very weakly with ordinary matter. Theoretically, when two WIMP particles collide, they should annihilate, releasing other particles, including gamma photons-light particles with very high energy. Astronomer Tomonori Totani from the University of Tokyo, using Fermi telescope data, reported detecting gamma rays consistent with predictions of WIMP particle annihilation. “We observed gamma rays with photon energies of 20 giga-electronvolts (GeV) emanating from a halo-like region in the direction of our galaxy’s center. The nature of the gamma ray emission closely matches the expected shape from a dark matter halo,” said Totani.
The observed energy spectrum-a distribution of gamma-ray intensity by energy-matches the spectrum predicted for the annihilation of hypothetical WIMP particles with mass roughly 500 times that of a proton. The annihilation frequency, estimated from the measured gamma-ray intensity, also falls within theoretical predictions. Importantly, these data are difficult to explain by other known astronomical phenomena or gamma-ray sources. Totani considers these data a significant indication of gamma radiation from dark matter, a long-sought quest.
“If the conclusion is confirmed, as far as I know, this will be the first time humanity has ‘seen’ dark matter. It would mean that dark matter is a new particle not included in the current Standard Model of particle physics. It will be a major event in astronomy and physics,” Totani stated. Despite Totani’s confidence, his results require independent verification by other scientists. Even after confirmation, evidence is needed that the radiation is indeed a result of dark matter annihilation and not from another astronomical phenomenon. Additional confirmation would come from detecting gamma rays of the same energy from other regions with high concentrations of dark matter, such as dwarf galaxies in the Milky Way halo. Totani hopes that further data gathering will provide more compelling evidence of dark matter’s existence.
