Galaxies expel matter in the form of winds – 12/06/2023 – Science

Galaxies expel matter to their closest surroundings in the form of galactic winds, according to a study published this Wednesday (6). The research authors observed this phenomenon in a large sample for the first time.

Two years ago, this phenomenon was observed for the first time in a galaxy, seen from the side, thanks to the Muse instrument of the VLT telescope, located in Chile. From the central region of its disk, two cones of gas loaded with matter emerged perpendicularly: the galactic winds.

“We can now generalize this observation across a large number of structures,” said Nicolas Bouché, an expert at the Center for Astrophysical Research in Lyon, France.

The scientist, who also participated in the observations two years ago, is one of the main authors of the study, published in Nature. The work concludes that the phenomenon of galactic winds appears “common” in massive galaxies.

A group of scientists, mainly from European institutes, studied a sample of more than 160 galaxies, seen in profile or head-on, located more than 7 billion light years away.

The Muse instrument, an integral field spectrograph, makes it possible to observe the trace of chemical elements in extremely diffuse, low-density clouds of matter. With a long exposure time of the VLT telescope on the sample of galaxies, Muse made it possible to draw the shape of the winds that emerge, detecting the trail of magnesium atoms.

Big star explosions

These winds “result from the explosions of supernovae, massive stars that collapse at the end of their lives, at a rate of 1 to 10 per century, depending on the type of galaxy”, Bouché explained to AFP. “Over millions of years, this adds up, forming galactic winds.”

They escape the galaxy mainly through its central region, where there is a greater concentration of stars. Rich in metals from supernovae, such as magnesium, they would play a key role in the formation of stars within galaxies.

“They could lead to a decrease in star formation” by disturbing the environment in which this happens, Bouché said. They would also regulate the amount of matter available to create these stars, since “the more matter the galactic winds carry, the less remains for star formation.”

The phenomenon appears to occur in the most common galaxies, of the order of 10 billion solar masses, less than that of the Milky Way.

The next puzzle to be solved is to determine how far these winds go, which have already been detected at distances of more than 30 thousand light years. They would have to be compared to galactic halos, composed of a galaxy and the galactic cloud that surrounds it, sets that can reach ten times that distance.

It’s about “knowing whether these winds and the matter they contain will fall back (into the galaxy, due to gravitational attraction) or whether they will escape to enrich the intergalactic environment”, highlighted Bouché. This on a time scale that could be quantified in billions of years.