The origin of the Fermi bubbles in the center of the Milky Way is being questioned

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[EN VIDÉO] Experience the first image of the supermassive black hole at the center of its galaxy!
A big step for our knowledge of these mysterious objects… We have been waiting for it since 2019, at the same time as the first image of the black hole M87*. It’s finally here: the very first photo of Sagittarius A*, the supermassive black hole at the heart of the Milky Way! © Futura

On either side of The Milky Way are two giant bubbles of X, gamma and radio, which forms a kind of “8” centered at the level of the galactic disk, or more precisely of the galactic center. Discovered by chance when researchers tracked black fabric in 2010 using space telescope Fermi Gamma-Ray, these well-defined bubbles span nearly 25,000 light years on each side of the disc. Furthermore, they continue to expand at a rate of 1,000 km/s. According to the researchers, they would be three million years old, with a energy of gamma rays between 1 and 100 GeV.

Their origins remain mysterious

But where do they come from? What were they made of? Given the special symmetrical shape of the Fermi bubbles, they could come from the galactic center, more precisely from central black hole, Sagittarius A*. This one would spit out high energy matter from its accretion disk. But a substructure located in the brightest region has intrigued an international team of researchers and is the subject of a publication in Natural astronomy.

This substructure, called according to the study, ” that cocoon », is closest to the galactic center and contains gas warm to over 8 million degrees Celsius so until today it was interpreted as coming from the same source as the rest of the Fermi bubbles.

Actually central black hole Sagittarius A* may have accreted a large amount of matter several million years ago, resulting in the ejection of gas and dust under high temperature and high velocity. This hypothesis, which did not reach consensus, has just been contradicted by the new study!

According to the researchers, the bottom of the bubbles “is probably due to galaxy Sagittarius Dwarf Spherical ». It is about 50,000 light years from the center of the Milky Way and orbit around our galaxy, which is being torn away little by little stars. Although it is no longer producing stars, according to the study, it would host a real one “population of pulsar milliseconds”that is, offneutron stars rotating at breakneck speeds.

The Sagittarius galaxy is hidden behind the galactic disc

But above all, “This large satellite of the Milky Way is seen through the Fermi bubbles from the position of Solar system », hence the researchers’ hypothesis, according to which it is actually only her that we see at the bottom of the bubbles Closed ! Or rather the millisecond pulsars it would contain. To be sure, they modeled several possible scenarios, including scenariosdischarge from black hole central and dwarf galaxies. It is the latter case that best corresponded to the observed measurements.

As for the millisecond pulsars in the Sagittarius galaxy, the researchers identified them as being responsible for elimination. No collision in the interstellar medium as gas from the galaxy was sucked in by the Milky Way. No supernovae either, because the latter release gas and the Fermi bubbles contain none. All that remained were the millisecond pulsars, the remnants of dead massive stars that emit powerful radiation from their poles.

A result that could complicate the search for black fabricbecause it is especially detected by gamma radiation emitted when dark matter particles and those antiparticles mutually annihilate each other. Finally, for researchers, “This finding plausibly suggests that millisecond pulsars produce significant γ-ray emission among old stellar populations, which could confound indirect searches for dark matter in regions such as the galactic center, the andromeda galaxy and other dwarf galaxies in the Milky Way. »

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