A long-held dark matter theory may have seen its first substantial evidence in its favor in the form of gamma rays being emitted in the Milky Way—an enormous potential discovery for the field of astrophysics.
Most people think that ordinary matter—that is, atoms, the stuff that makes up the tangible parts of our world—compose the entire universe. But in reality, normal matter only composes less than five percent, while dark matter and dark energy make up the rest.
To put it very simply, dark matter is an intangible substance which can’t be detected directly, but which adds mass in the places where it exists. Because it adds mass, it increases alters the gravity around it—meaning its effects on stars and normal matter around it has been how we’ve determined its presence.
Theories surrounding the mysterious matter
Physicists currently have many theories about what comprises dark matter, but some believe that, besides gravity, it shares another property in common with regular matter—it comes in both a regular dark matter form and an anti-matter form. When these two forms collide, they annihilate, meaning the particles themselves more or less cancel out. However, their energy and momentum are conserved, and a new high-energy particle is formed, like a photon or a gamma-ray.
According to the paper in Physics of the Dark Universe, researchers believe that have identified one such signature of dark matter annihilation in the Milky Way. In particular, they focused on how gamma-ray emission was distributed throughout the Galactic Center region of the galaxy—an area that has high matter density (as a slightly higher density of dark matter, too).
Should dark matter consist of particles and anti-particles, annihilation would occur in this area, and thus it would be bright in gamma-rays. And in fact, scientists have detected a large gamma-ray signature that extends hundreds of light-years beyond the Galactic Center region.
Of course, there are other sources of gamma-rays. Pulsars—neutron stars that emit electromagnetic radiation—might have been culprits, for example. And so the scientists carefully revisited some previously-published gamma-ray observations, applying new data reduction methods to better pinpoint the location of gamma-ray emission.
After applying these methods, the scientists demonstrated that the distribution of the radiation fit significantly better with models of annihilating dark mark than with pulsar models—meaning that they have found good evidence in favor of dark matter anti-particles, an enormous breakthrough in understanding part of the fabric of the cosmos.
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