Image of a galaxy taken by the Hubble telescope, 70 million light years from Earth.

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ESA / HUBBLE & NASA / AFP

Astronomers have established for the first time that missing dark matter from one galaxy is being torn off by gravitational forces from another larger one, according to a study cited at the Hubble Space Telescope website.

"This discovery reconciles our current knowledge of the formation and evolution of galaxies with the most common cosmological model," says Mireia Montes, astronomer at the Australian University of New South Wales, lead author of the published study. in Astrophysical Journal.

Astrophysicists have been facing a challenge since 2018, the year of the discovery of a first galaxy, NGC 1052-DF2, devoid of dark matter.

How to explain its existence without this invisible and mysterious element, which is supposed to act as a kind of "glue" by its gravitational force to ensure its cohesion?

Identified theoretically, dark matter owes its name to the fact that no one has observed or described it.

It would form more than 25% of the Universe.

The globular clusters are "torn off"

In 2019, astronomers discovered a second galaxy, NGC 1052-DF4, also almost completely devoid of dark matter.

Dr. Montes' team used the Hubble Space Telescope to detail the contents of the galaxy, including its globular clusters, very dense groups of stars orbiting at its center.

It also used the GTC, the large Spanish Canary Islands telescope to analyze the light from NGC 1052-DF4, located 45 million light-years from Earth.

The team concluded that "the absence of dark matter can be explained by the effect of a tidal force".

That is, the gravitational forces of a nearby massive galaxy, NGC 1035, are disrupting its smaller neighbor.

Scientists draw this conclusion by observing that globular clusters are "torn" from their host galaxy and that we identify tidal tails, kinds of filaments of stars and stellar gas, characteristic of this dislocation.

“Ultimately, NGC 1052-DF4 will be cannibalized by the large system surrounding NGC 1035, with at least some of its stars floating freely in deep space,” explains Ignacio Trujillo, of the Canary Islands Institute of Astrophysics, co-author of the study cited in the press release.

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