Thousands of galaxies are disappearing mysteriously

                                 The American Toby Brown is not just astrophysicist. He also appears as the protagonist of a cosmic version of the TV series Criminal Minds, and has just discovered the identity of a bloodthirsty serial killer: the overheated intergalactic plasma. Your victims? Whole galaxies.

It's to leave Jack the Ripper with envy. Brown's team, which is an astronomer at the International Institute for Radio astronomy Research (ICRAR) in Australia, has observed 11,000 galaxies in the nearby universe. In several of them, a cloud of gas containing hydrogen, helium, and smaller amounts of heavier elements, which served as raw material for star formation, was being swept away by a kind of invisible vacuum cleaner. Conclusion? As existing stars aged, the galaxy, unable to make new ones, lost its glow until it died. Artistic projections provided by the agency provide an idea of ​​the crime scene: it is easy to see large concentrations of gas separating from the galaxy NGC 4921, located 320 million light-years away from Earth. An animation is available on the ICRAR channel on Vímeo.

But why, after all, does this happen? Although the overheated intergalactic plasma, the scientific name of the vacuum cleaner, has a fair amount of guilt in the registry, it is only the weapon used by something much more mysterious: dark matter.

All you can see is only 5% of everything that exists in the universe. The remaining 95% are divided into 27% dark matter and 68% dark energy, both invisible and undetectable. The existence of dark matter can only be deduced from its gravitational influence on the portion of the cosmos that we can see and investigate, called baryonic matter.

That is, we know through physics and mathematics that this immense ghostly mass must be where it is to explain the equilibrium of the universe. Got scared? Do not think that the problem is far from you. A well-accepted hypothesis, for example, is that all galaxies - including the Milky Way - are plunged into halos of dark matter, called halos. This structure plays a key role in the models and simulations that explain the formation and evolution of stars - that is, it is very likely that there is one of those around us.

"During its lifetime, a galaxy can inhabit halos of different sizes, with masses that can be equal to that of the Milky Way or even thousands of times larger," Brown explained on the INCRA press page. And it's time to jump from one halo to the next that the mysterious killer comes into action.

As the galaxy gets stuck between the old halo and the new halo, the plasma (which stays in the open, overheated space) begins to extract the raw material from the stars by force. "It's like a blow to the head. In a few tens of millions of years, the gas has ended - from an astronomical point of view, that is very fast, "the astronomer told advisory.

According to the team, it was already known that this process, whose scientific name is ram-pressure stripping, occurred in clusters of larger galaxies with massive halos. But this was the first time the phenomenon was seen in smaller clusters, sometimes with only two galaxies. Sad, is not it? If it serves as a consolation, the other option for the end of a galaxy is a kind of suicide, which occurs when star formation is faster than the ability to replenish the gas.