We have come to know that most of the matter in the universe is dark. This so-called dark matter is a material that is so elusive that after decades of trying we are still not able to point to a piece of it and say, “Look, there it is.”
Even if we cannot pick it up with our hands, there are at least different ways to try to see where this dark matter is hiding. For example, experimental physicists are trying to find dark matter on the ground (actually underground) on the assumption that every once in a while it may have a property such that it interacts with ordinary matter.
Meanwhile astronomers are using various approaches to try to find dark matter in outer space. Some are looking at understanding why stars orbit so strangely within galaxies. Others are looking at the light from distant galaxies and seeing how it gets distorted by the presence of large natural telescopes along the long path from the source to Earth by a phenomenon called gravitational lensing.
Still others are looking at high energy radiation from the center of our own Galaxy. It turns out that the center of the Milky Way galaxy is a kind of X-ray and gamma-ray producing machine.
Gamma rays have the highest energies of all radiation, equating to billions of electron volts, or GeV. The high energy radiation that cannot be explained by radiation in any other way is thus known as the “GeV excess.”
About 10 years ago it was proposed that a good part of this GeV excess radiation may be a result of dark matter interacting with ordinary matter. There was not a complete consensus on this interpretation at the time, but neither was there a better idea put forward.
Just this past summer there emerged a more mundane solution which may turn out to be correct. Now it appears that stars can also produce GeV radiation, not ordinary stars, but spinning neutron stars pulsars. In particular, there are some pulsars which spin more than a thousand times per second.
These ultra-fast spinning pulsars are rare, but there may be enough of them near to the Galactic center to explain the GeV excess without the need for dark matter annihilation processes. If so, then it looks like nature manages to keep holding onto her secrets of what the dark matter is, for now.