An ancient collision left a chain of galaxies without dark matter

(ORDO NEWS) — Astronomers have discovered a structure of a dozen dwarf galaxies, elongated in an uneven chain and devoid of dark matter. Perhaps all this is the remains of a cosmic catastrophe that blew a couple of ancient galaxies to pieces.

The movements of distant stars and galaxies show that they experience the attraction of invisible dark matter (there is several times more of it than ordinary matter, of which the galaxies and stars themselves are composed).

The nature of dark matter remains unknown, but it determines the formation of large-scale structures of the Universe, dominates in star clusters, galaxies and their clusters.

Only recently have astronomers begun to discover galaxies that are completely devoid of dark matter or contain it in extremely small quantities.

Like, for example, the dwarf NGC 1052-DF2 (or simply DF2), which was found a couple of years ago by the team of Pieter van Dokkum (Pieter van Dokkum) from Yale University.

Since then, several more similar objects have been discovered, including DF4, located near DF2. These galaxies are very baffling to scientists trying to understand how they could have formed without dark matter, or how they lost it.

An ancient collision left a chain of galaxies without dark matter 2

One of the hypotheses connects their appearance with collisions of galaxies. As a result of such an “accident”, the masses of their dark matter can continue their journey, passing through each other.

But the clouds of ordinary matter experience pressure from each other, slow down, interacting, and separate from the dark matter. This scenario is also indicated by a new paper by van Dokkum and his colleagues, published in the journal Nature .

Observations of DF2 and DF4 showed that the trajectories of these galaxies began to diverge from a common point about eight billion years ago.

Moreover, along with them, other dwarf galaxies, poor in dark matter, began to move. Today, DF2 and DF4 are part of a chain of seven to 11 such objects located at a distance of about 70 million light-years from us.

Scientists suggest that this structure may be the trace of one impressive and ancient catastrophe. Then the galaxies, having collided, lost their dark matter, and their ordinary matter, interacting, formed new clusters that stretched out as a chain of dwarf galaxies.

At the leading end of the resulting structure, astronomers noticed dark matter-like clumps of formations, possible remnants of the same collision.

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