The mysterious ultra-bright gamma-ray emission in the giant bubbles blown by our galaxy may finally have an explanation.
The researchers used data from Gaya and Fermi space telescopes to search through Fermi bubbles, a pair of colossal hourglass-shaped bubbles radiating from the poles The Milky Way and span 50,000 light-years to trace the source of very bright patches of gamma-ray emission.
They found that one of the brightest of these spots, dubbed the “Fermi cocoon,” located in the southern bubble, was caused by radiation from fast-spinning, dead stars called pulsars in the Milky Way. satellite of the Sagittarius galaxy. The finding could shed light on how these collapsed dead stars act as cosmic particle accelerators, blasting out high-energy particles that go on to produce gamma-rays.
Gamma rays have previously 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 cannot be evidence of dark matter.
A view of the dwarf satellite galaxy Sagittarius 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 narrow orbit passed through the disk of the Milky Way.
Gamma rays are thought to be produced by young stars, annihilation of dark matter, or millisecond pulsars. This violent expulsion of gas means that the Sagittarius dwarf galaxy is no longer forming stars and has no stellar nursery, so its gamma-ray emission cannot be the result of young stars.
Furthermore, the shape of the Fermi cocoon closely matches the observed distribution of visible stars, ruling out dark matter as the source of the radiation. (If dark matter were present, its gravity would affect the shape of the cocoon). The researchers therefore concluded that the only possible sources of this powerful radiation were a previously unknown population of millisecond pulsars, which are rapidly rotating, ultra-dense stellar remnants that spin hundreds of times per second.
“We are satisfied that there is only one possibility: rapidly rotating objects called ‘millisecond pulsars,'” wrote a team at the Australian National University statement (opens in a new tab). “Millisecond pulsars in the Sagittarius dwarf were the ultimate source of the mysterious cocoon, we found.”
Like all neutron stars, a pulsar forms when the star is much more massive 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 support itself against total gravitational collapse. Accompanied by mass supernova explosion, the gravitational collapse leaves behind a star the size of a city with a mass similar to that of the sun. This stellar remnant consists of matter so dense that a teaspoon of it would weigh 4 billion tons.
Scientists believe that the rapid spin of millisecond pulsars is caused by the accretion of matter from the binary companion star, which adds angular momentum to the dead star — or “spins it up.”
Due to their powerful magnetic fields, the poles of pulsars explode electrons and positrons (electrons) antimatter equivalents). When electrons interact with low-energy photons that make up cosmic microwave background (CMB) is the radiation left over from shortly after Big explosion — electrons transfer 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 results suggest that the gamma-ray emission in Fermi bubbles is not the result of dark matter annihilation, the researchers said.
“This is important because dark matter researchers have long believed that observing gamma rays from a dwarf satellite would be a sign of dark matter annihilation,” said one of the team’s leaders, Oscar Macias, a researcher at the University of Amsterdam. in statement. (opens in a new tab) “Our study forces a reassessment of the high-energy emission potential of stationary stellar objects such as dwarf spheroidal galaxies and their role as prime targets for the search for dark matter annihilation.”
The team’s research was published online Sept. 5 in the journal Science Astronomy of nature (opens in a new tab).
https://www.space.com/gamma-ray-cocoon-sagittarius-dwarf-galaxy/ Dead stars in the Milky Way’s companion galaxy create a gamma cocoon