The mysterious emissions of ultrabright gamma rays in the giant bubbles blown by our galaxy may finally have an explanation.
The researchers used data from the Gaia and Closed space telescopes to search through the Fermi Bubbles, a pair of colossal hourglass-shaped bubbles that extend from the poles of the Milky Way and span 50,000 light-years, to trace the source of the very bright gamma-ray emission spots.
They found that one of the brightest of these spots, dubbed “Fermi’s cocoon”, located in the southern bubble, was caused by emissions from rapidly rotating dead stars called pulsars in the Lane satellite galaxy Sagittarius. milky. The discovery could shed light on how these dead, collapsed stars act as cosmic particle accelerators, shooting out high-energy particles that cause gamma ray emissions.
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Gamma rays have already been highlighted as a possible result of the annihilation of dark matter. But if gamma rays are the result of particles accelerated by pulsars, they may not be proof of dark matter.
The Sagittarius dwarf satellite galaxy is seen from Earth through the Fermi Bubbles and is marked by elongated streams of gas and stars that were torn from the galaxy’s core as its tight orbit passed it through the Milky Way’s disk.
Gamma ray emissions are thought to be created by young stars, dark matter annihilation, or millisecond pulsars. This Violent Gas Vent Means The Sagittarius Dwarf Galaxy Is No Longer Forming stars and lacks stellar nurseries, so its gamma ray emissions cannot be the result of young stars.
Moreover, the shape of Fermi’s cocoon closely matches the observed distribution of visible stars, ruling out dark matter as the source of the emissions. (If dark matter were present, its gravity would affect the shape of the cocoon). Thus, the researchers concluded that the only possible sources of this powerful radiation were a previously unknown population of millisecond pulsars, which are fast-rotating, ultra-dense stellar remnants that spin hundreds of times per second.
“We are confident that there is only one possibility: rapidly rotating objects called ‘millisecond pulsars’,” the team wrote at an Australian national university. statement (opens in a new tab). “The Sagittarius dwarf’s millisecond pulsars were the ultimate source of the mysterious cocoon, we have discovered.”
Like all neutron stars, a pulsar forms when a star much more massive than the Sun reaches the end of its life and can no longer perform nuclear fusion at its core. As a result, it can no longer sustain itself against complete gravitational collapse. Accompanied by a massive supernova explosion, the gravitational collapse leaves behind a star the size of a city with a mass around that of the sun. This stellar remnant is made of matter so dense that a teaspoon would weigh 4 billion tons.
Scientists believe that the rapid rotation of millisecond pulsars is caused by material accretion from a binary companion star that adds angular momentum to the dead star – or “spins” it.
Due to their strong magnetic fields, the poles of pulsars explode electrons and positrons (electrons antimatter equivalents). When the electrons interact with the low energy photons that make up the cosmic microwave background (CMB) – radiation remaining shortly after the big Bang — the electrons give up part of their kinetic energy. This causes the CMB photons to become much more energetic gamma photons.
By demonstrating that the gamma-ray cocoon is the result of pulsars, the team’s findings suggest that gamma-ray emissions in Fermi bubbles are not the result of dark matter annihilation, the researchers said. .
“This is important because dark matter researchers have long believed that a sighting of gamma rays from a dwarf satellite would be a smoldering signature for dark matter annihilation,” said the co-lead of the research. team Oscar Macias, researcher at the University of Amsterdam. in a statement. (opens in a new tab) “Our study forces a reassessment of the high-energy emission capabilities of quiescent stellar objects, such as dwarf spheroidal galaxies, and their role as prime targets for dark matter annihilation research.”
The team’s research was published online September 5 in the journal natural astronomy (opens in a new tab).
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