The Fermi Bubbles, two orbs roughly 25,000 light-years large loaded with hot gas and cosmic rays, are located above and below the Milky Way’s plane. They are also a significant source of gamma rays. The Fermi Cocoon, a mystery feature with no known source up to this point, is one of their bright spots. The culprit, according to astronomers, is a galaxy that is progressively being obliterated by our own.
This little galaxy, also known as the Sagittarius Dwarf, is a spheroidal galaxy that the Milky Way “unspooled” about a billion years ago. This tiny satellite’s orbiting of our galaxy has resulted in the cannibalization of much of its gas and many of its stars.
From the perspective of the Solar System, the dwarf galaxy can be seen directly through the Fermi bubbles and corresponds to the location of the Fermi Cocoon, but the gamma-ray emission is difficult to explain in the absence of new, massive stars being created and then going supernova. Two theories were put up by astronomers: either the dwarf galaxy contains a population of millisecond pulsars waiting to be found, or the annihilation of dark matter, which has been sought after for a long time, was being observed.
The pulsar scenario is the most likely, according to their article that was published in Nature Astronomy. As the result of some massive (but not overly massive) stars going supernova, pulsars are a particular sort of neutron star. They spin while emitting radiation bursts at various wavelengths, including gamma rays. As the name implies, millisecond pulsars periodically rotate on their axes.
In fact, the Fermi bubbles were found as scientists were searching for proof that dark matter, the fictitious substance that surrounds all galaxies, would possibly be able to create gamma rays. This new work challenges presumptions about dwarf galaxies being a good target for such searches.
This is noteworthy because, according to co-author Dr. Oscar Macias of the University of Amsterdam, “dark matter experts have long felt that a discovery of gamma rays from a dwarf satellite would be a smoking gun signature for dark matter destruction.”
“Our finding necessitates a reevaluation of the high energy emission properties of inactive star objects, like as dwarf spheroidal galaxies, and their position as primary targets for dark matter annihilation searches,” the authors write.
According to the research team, the Fermi Cocoon is a region where photons from the cosmic microwave background are accelerated to gamma-ray energies as a result of the high-energy particles produced by pulsars.