Gamma rays are detected in unusually high amounts at the center of the Milky Way galaxy
The center of our galaxy is exhibiting unusual behavior, potentially linked to dark matter. In 2009, observations from the Fermi Gamma-ray Space Telescope uncovered unexpectedly high levels of gamma ray emissions from the Milky Way’s center, a phenomenon termed galactic central gamma-ray excess (GCE). Simulations suggest these gamma rays could arise from the annihilation of dark matter particles.
The discussion surrounding the origins of GCE has intensified since its initial discovery, leading to two main theories. The first posits that it may stem from a previously unobserved population of pulsars, rapidly spinning neutron stars that emit considerable radiation.
Alternatively, it could be linked to weakly interacting massive particles (WIMPs), long considered primary candidates for dark matter. These particles seldom interact with normal matter, but a collision between two can lead to annihilation and consequently, a burst of gamma rays.
However, the dark matter explanation has lost traction recently, especially after searches for WIMPs yielded no results. “The dark matter interpretation demands greater proof due to insufficient direct evidence of its existence despite thorough investigations,” notes Jeff Grube from King’s College London.
Another factor contributing to this skepticism is that dark matter in galaxies is expected to be evenly distributed, while GCEs display a flattened distribution. Yet, new simulations by Joseph Silk and his colleagues at Johns Hopkins University in Maryland indicate that this discrepancy may not be significant.
These new simulations carefully considered the Milky Way’s history in relation to GCEs. “We know from history that our galaxy merged with smaller galaxies billions of years ago, which contributed to the formation of dark matter,” noted Silk. “No one would have anticipated that the galaxy’s center would exhibit spherical symmetry due to this history.”
The results confirmed this notion, resulting in a distorted dark matter distribution aligned with the shape of GCE, reviving the dark matter theory. However, the mystery remains unresolved, as pulsars continue to be a viable explanation. “At best, the situation is still ambiguous,” added Grube.
The current gamma-ray observatories do not possess the capability to distinguish between these two theories; however, the Cherenkov Telescope Array observatories, under construction in the Canary Islands and Chile and expected to begin operations in 2026, could provide clarity.
“In many ways, there’s a 50 percent chance that we may have discovered significant dark matter, but we require new telescopes to confirm this,” stated Silk. If GCE is indeed the result of dark matter, it could offer the best insight yet into this enigmatic substance that underpins the universe.
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Source: www.newscientist.com
