Galactic winds: When galaxies eject matter – Le Journal de Montréal

Galaxies eject matter into their immediate surroundings in the form of galactic winds, according to a study published Wednesday by researchers who observed the phenomenon for the first time in a large sample of star clusters.

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The MUSE instrument of the Very Large European Telescope (VLT) in Chile made the first observation of this phenomenon on a galaxy seen from the edge two years ago.

From the central area of ​​its disk, two gas cones loaded with matter, which are galactic winds, escaped perpendicularly on either side.

“Now we can extend this observation to a large number of structures,” says Nicolas Bouché, an astrophysicist at the Lyon Astrophysical Research Center.

The researcher, who was already at the center of the observations carried out two years ago, is one of the main signatories of the study published in Nature, which concludes that the phenomenon of galactic winds appears to be “common” in massive galaxies.

A large number of scientists from mainly European institutes examined a selection of more than 160 galaxies, viewed from the side or from the front. They are more than seven billion light-years away and bear witness to a universe that is about half its current age.

The MUSE instrument, an integral field spectroscope, allows observation of the signature of chemical elements in extremely diffuse, low-density matter clouds.

Using a very long exposure time of the VLT telescope on the sample of galaxies, MUSE made it possible to draw the shape of the outflowing winds by detecting the signature of magnesium atoms.

Massive stellar explosions

These winds “arise from explosions of supernovae, massive stars that explode at the end of their lives, at a rate of one to ten per century, depending on the type of galaxy,” explains Nicolas Bouché to AFP.

“Galactic winds add up over millions of years,” adds the researcher. These winds escape the galaxy mainly through its central region, as this is where most stars and therefore supernovae are concentrated.

These winds are rich in supernova metals like magnesium and play a key role in star formation in galaxies.

According to the researcher, they can “cause a decline in star formation” by disrupting the environment in which they form. They would also regulate the amount of material available to form these stars, because “the more material is carried away by galactic winds, the less is left for star formation.”

The phenomenon appears to be widespread in the most common galaxies, with a mass of about ten billion solar masses – less than that of our Milky Way.

The next puzzle to solve is figuring out how far these winds extend, which the study detected at distances of more than 30,000 light-years. Compare it to galactic halos, which consist of a galaxy and its surrounding galactic cloud: these quantities easily reach ten times this distance.

It’s about “knowing whether these winds and the matter they contain will later fall back or escape (from the galaxy: editor’s note) in order to enrich the intergalactic environment,” emphasizes Nicolas Bouché.

And on time scales that are not child’s play: they could be counted “in billions of years.”

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