American astronomers have discovered that the mysterious gamma radiation emanating from the center of the Galaxy is not associated with the decays of dark matter, but with several hundred pulsars. This is stated in an article sent to publication in the Astrophysical Journal.
“Our observations show that dark matter is not needed to explain why we see excess gamma radiation emanating from the center of our Galaxy. We found a large population of pulsars in the regions surrounding the center of the Milky Way, which made us take a fresh look at the history of its formation,”says Mattia Di Mauro from Stanford University (USA).
For several years now, Di Mauro and other scientists from the Fermi collaboration have been investigating one of the most important mysteries of the Galaxy - why its central part produces noticeably more gamma radiation in the high-energy part of the spectrum than predicted by calculations based on the density of distribution of stars and activity in the center of the black holes.
This phenomenon, discovered by the Fermi telescope in 2009, has led many scientists to believe the excess of gamma rays is a consequence of the decay of dark matter particles in the center of the Milky Way. Therefore, astrophysicists and cosmologists constantly monitor the central part of the Galaxy, trying to confirm or deny this idea, and also look for similar traces of gamma radiation in the cores of other galaxies.
From the point of view of astrophysics, to refute it, it is necessary to show that gamma photons from the center of the Milky Way fly towards us from point light sources, which can be pulsars or other compact objects. If they are generated by decaying dark matter particles, the excess radiation will be evenly distributed across the sky.
Di Mauro and other astronomers working with Fermi have come close to solving the gamma puzzle of the Milky Way, having found about four hundred pulsars emitting in the gamma range in images of the galactic center. The key to the discovery was new algorithms to improve the quality of the picture, thanks to which scientists for the first time were able to "see" the point sources of the pulsar glow.
As noted by Di Mauro, pulsars differ from other sources of gamma radiation (supernovae, active galactic nuclei and ionized gas) in that the structure of the spectrum of their radiation strongly depends on where the glow peak in the gamma range is located.
Guided by this idea, scientists analyzed the latest images of the galactic center, obtained using the LAT instrument aboard Fermi, and found about four hundred pulsars on the outskirts of the Milky Way's core. Astronomers are one hundred percent sure of the existence of 66 of them. In total, as the calculations of di Mauro and his colleagues show, there may be about 1300 pulsars in the center of the Galaxy, the gamma radiation of which will be enough to explain the anomaly discovered by Fermi almost ten years ago.
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As the scientist notes, the discovery of such a large number of gamma pulsars was a relative surprise for his team. Pulsars - the remains of long-dead stars that have exhausted their reserves of hydrogen and helium - live in this state for a relatively short time by cosmic standards, about five to ten million years.
On the other hand, the galactic center is one of the most ancient parts of the Milky Way, and it is highly unlikely that all of these pulsars formed in the last 10 million years. This, according to Di Mauro, suggests that most gamma pulsars do not live there alone, but in the company of another star, whose matter they periodically steal in order to "spin" themselves.
Does this mean that dark matter does not exist? As Di Mauro emphasizes, the discovery only says that dark matter particles do not decay at the centers of galaxies and behave differently than previously thought. In the near future, the Fermi team plans to conduct more detailed observations of these pulsars using ground-based radio telescopes capable of capturing their pulsations and finally proving that dark matter is not to blame for the excess of gamma rays.