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Milky Way: Cosmic mystery of satellite galaxies solved

2023-01-02T14:16:38.432Z


So far, science has had no explanation for this: the galaxies around the Milky Way lie almost in one line. This actually contradicts the standard cosmological model.


Enlarge image

Galaxies almost in one line: That shouldn't really exist - or should it?

Photo: Till Sawala / Sibelius collaboration / dpa

For decades, astronomers have puzzled over why the Milky Way's satellite galaxies are not evenly distributed, but lie within one disk.

Because that cannot be explained in the standard cosmological model.

An international team of researchers is now presenting an explanation for the supposed cosmic mystery based on more precise measurements: the arrangement is pure coincidence.

Today's unusual position will disappear again within a few hundred million years due to the movement of the galaxies, the scientists write in the journal "Nature Astronomy". 

"The companions of the Milky Way are almost aligned in the sky - and this has puzzled astronomers for decades," explains co-author Carlos Frenk of Durham University in the UK.

Because if the satellite galaxies are aligned in the sky, they must all be within a thin disk in space.

"And explaining that is extraordinarily difficult for cosmology." So difficult that it has already led to doubts about the standard cosmological model and, in particular, about the researchers' idea of ​​the mysterious dark matter.

densification of dark matter

According to current knowledge, the visible matter - i.e. stars, planets or gas clouds - contributes only one fifth of the total mass of the cosmos.

Eighty percent of the mass consists of dark matter.

This is completely invisible - hence its name - and reveals itself only through its power of attraction.

Dark matter plays a crucial role in the formation of galaxies in the cosmos.

Computer simulations show how normal matter accumulates in large concentrations of dark matter.

These concentrations of dark matter are spherical in shape, and the galaxies that form within them are randomly distributed.

A concentration in a disk cannot be explained in this model and is also not shown in the computer simulations.

Space telescope provides explanation

Frenk and his colleagues have now used the best data to date from the European Space Agency's Gaia space telescope to solve this mystery.

Gaia has been in space since 2013 and provides precise position and motion data for about a billion stars - not only in our Milky Way, but also in its satellite galaxies.

The evaluation of the data caused a surprise.

Until now, astronomers had assumed that the small galaxies always moved on orbits within the disk.

But that is not the case.

The conclusion of Frenk and his colleagues: The currently observed concentration of satellite galaxies in a disk is purely coincidental.

Within a few hundred million years - a short time in cosmological terms - the disc has disappeared and the galaxies are once again evenly distributed around the Milky Way.

"We have thus solved one of the currently greatest challenges of the cosmological model," says Frenk happily.

"The dark matter model gives us a remarkably accurate description of the evolution of the universe."

koe/dpa

Source: spiegel

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