Dark matter is one of the greatest revelations in modern physics. Even though it hasn’t been directly detected yet, we know that it makes up around five-sixths of the total matter in the universe, binding much of it together in dramatic ways. It is this matter that stops galaxies from being torn apart as they spin.
As a new study published in the journal Physics of the Dark Universe notes, dark matter can also be destroyed. A signature of dark matter’s annihilation could potentially reveal what it was composed of in the first place, and this team of researchers from Harvard University think they’ve found one right in the heart of our own Milky Way.
Scientists are still debating what dark matter may actually be composed of, and one recent suggestion implies the particles are so dense that they are on the verge of becoming miniature black holes. Whatever they turn out to be, many astrophysicists think that these particles share a property with “ordinary” matter: they come in two flavors, matter and antimatter. When matter encounters antimatter, both are destroyed in a powerful blast that emits high-energy radiation.
This team of researchers have been looking for a source of matter-antimatter annihilation, but with dark matter, not ordinary matter. Peering into the galactic center, where the density of matter – and presumably dark matter – is incredibly high, previous studies have spotted powerful emissions of gamma-rays. One possibility is that this energetic signal originated from a particle of dark matter colliding with its antimatter equivalent, destroying each other in the process.
However, the team realized there were many other celestial events that could produce this type of outburst. As a recent high-resolution map of every single bright object in deep space shows, the universe is fiery and energetic, throughout all of time and space in fact – neutron stars, merging black holes, supernovae and their subsequent glowing, nuclear ashes can all emit gamma-rays.
Nailing down the gamma-ray signal, it appears to be coming from the galactic center in an area not known for the presence of pulsars. Daylan et al./Physics of the Dark Universe
Pulsars are a type of neutron star, and are often known as the “lighthouses of the universe.” They rotate at inconceivable speeds and emit beams of electromagnetic radiation. If these beams crossed your path, they would look like high-energy pulses. The researchers thought that, based on current theoretical models of dark matter, the dramatic gamma-ray emissions observed coming from the galactic center could only be manufactured by a pulsar or dark matter annihilation.
If it was produced by a pulsar, the pulsar itself needed to be located. Pulsars are normally found near other star clusters, but after careful analysis, they concluded that the region of the galactic center the gamma-ray burst came from was unlikely to contain pulsars. By the process of elimination, it seems that this burst may have come from the destruction of dark matter.
“The signal described in this study can be explained by a very simple dark matter candidate, without any baroque or otherwise unexpected features,” the authors write in their study. If confirmed, this discovery has “profound implications for cosmology and particle physics.”
A billion particles of dark matter pass through your hand every single second, so it would be good to know what they’re made of – and this annihilation signal may actually shed some light on this.