On either side of the Milky Way, two large areas extend and form a kind of eight: the Fermi bubbles. Researchers have looked into their origin, and have identified it as being different from what was considered until today.

Discover 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’ve been waiting for it since 2019, at the same time as the first image of the M87* black hole. 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 gigantic bubbles of X, gamma and radio radiation, which form a kind of “8” centered at the level of the galactic disc, or more precisely of the galactic center. Discovered by chance when researchers were tracking dark matter in 2010 using the Fermi Gamma-Ray space telescope, these well-defined bubbles extend over nearly 25,000 light years on each side of the disk. Moreover, 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 gamma ray energy between 1 and 100 GeV.

Their origin remains mysterious

But where do they come from? By what were they created? Given the particular symmetrical shape of the Fermi bubbles, they could come from the galactic center, more precisely from the central black hole, Sagittarius A*. This would spit out high-energy matter from its accretion disk.

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

Indeed, the central black hole Sagittarius A* could have accreted a large amount of matter several million years ago, resulting in an ejection of gas and dust under high temperature and at high speed. This hypothesis, which however did not achieve consensus, has just been contradicted by the new study!

According to the researchers, the base of the bubbles “is probably due to the Sagittarius dwarf spheroidal galaxy”. It is about 50,000 light-years from the center of the Milky Way and orbits around our Galaxy, being gradually torn from the stars. Although it no longer produces stars, it would house, according to the study, a veritable “population of millisecond pulsars”, that is to say neutron stars rotating at dizzying speeds.

The Sagittarius galaxy hides behind the galactic disc

But above all, “this large satellite of the Milky Way is seen through the Fermi bubbles from the position of the Solar System”, hence the hypothesis of the researchers according to which, it is in fact only her that we see at the base of Fermi bubbles! Or rather, the millisecond pulsars it would contain. To make sure, they modeled several possible scenarios, including that of the emission from the central black hole, and that of the dwarf galaxy. It is the latter case that best corresponded to the measurements observed.

As for the millisecond pulsars within the Sagittarius galaxy, the researchers identified them as being responsible by elimination. No collision within the interstellar medium, as gas from the galaxy was sucked in by the Milky Way. No supernovas either, because the latter release gas, and the Fermi bubbles do not contain any. 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 dark matter, because it is detected in particular by gamma radiation emitted when particles of dark matter and antiparticles annihilate each other. Finally, for the researchers, “this finding plausibly suggests that millisecond pulsars produce significant γ-ray emission among ancient stellar populations, which could confound indirect searches for dark matter in regions such as the galactic center, the Andromeda Galaxy and other Milky Way dwarf galaxies. »

Dwarf Galaxy Gamma Rays Solve Astronomical Puzzle

Astronomers have been wondering about a mysterious point in our galaxy for ten years.

The “cocoon”, a point of light, has intrigued astronomers since its discovery. The spot is in our galaxy and has interested researchers for at least 10 years.

Detect gamma rays with a telescope

On Earth, gamma rays are successfully blocked by our atmosphere. As a result, researchers had no idea how abundant this gamma sky was before sending the appropriate instruments into space. The most advanced gamma-ray instrument in use today is this Gamma-ray Fermi Space Telescope. It’s part of a big Nasa-Assignment. This allows details to be seen and even weak sources of gamma rays to be identified. A few surprises have already been discovered.

In 2010, for example, mysterious bubbles appeared in the center of the Milky Way. This Fermi Bubbles overcast about 10 percent of the sky. It has now become clear that these also come from gamma rays from the Sagittarius dwarf galaxy. But why do the rays come from there? Researchers searched for an explanation.

Millisecond pulsars as a cause

They now accuse the so-called millisecond pulsars, that is to say rapidly rotating objects. These are remnants of stars significantly more massive than the Sun. Under the right circumstances, such binary star systems produce a neutron star who hundreds of times per second turns.

Due to their rapid rotation and strong magnetic field, these neutron stars appear as natural stars particle accelerator: They shoot particles of extremely high energy into space. These particles then emit gamma rays. These are also the cause of the mysterious cocoon. This is how the researchers discovered the mystery.

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