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Dark matter in motion | space



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  Two patches that look very similar

The formation of stars in small dwarf galaxies can slowly heat up the dark matter and push it outwards, according to a new study. On the left, the hydrogen gas density of a simulated dwarf galaxy from above. Right, the same goes for a real dwarf galaxy, IC 1613. In the simulation, the repeated gas supply and outflow causes the gravitational field strength in the center of the dwarf galaxy to fluctuate. The dark matter responds with a migration from the center of the galaxy, an effect called "warming of dark matter". Image via J. Read et al.

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Scientists have found evidence that dark matter can be heated and moved by star formation in galaxies. The results provide the first observable evidence for the effect known as Warming of Dark Matter and provide new clues as to what dark matter constitutes. The study was published on January 3, 2018 in the peer-reviewed journal Monthly Notices of the Royal Astronomical Society .

In the new work, an international team of scientists set out to find evidence of darkness matter in the centers of nearby dwarf galaxies. Dwarf galaxies are small, weak galaxies that normally orbit larger galaxies like our own Milky Way galaxy. They are an integral part of the discussion of dark matter because they appear to have even higher levels of dark matter than larger galaxies, and because the primary theory of dark matter – the theory of cold dark matter – suggests that there are many more dwarf galaxies which orbits our Milky Way and other galaxies than were found.

It is believed that dark matter accounts for a significant percentage of the mass of the universe. However, since it does not interact with light like normal matter, it can only be observed by its gravitational effects. The key to investigation might be how stars are formed in galaxies.

  Pie chart of the universe with 68.3% dark energy, 26.8% dark matter, and 4.9% of ordinary matter.

The composition of the universe was determined by analysis of the cosmic microwave background data of the Planck mission. Picture via University of Oxford / © ESA.

When stars form, strong winds can keep gas and dust out of the heart of the galaxy. As a result, the center of the galaxy has less mass, which affects how much gravity is perceived by the remaining dark matter. With less attraction, dark matter gains energy and wanders away from the center, an effect called dark matter .

The team of astrophysicists measured the amount of dark matter in the centers of 16 dwarf galaxies with very different star formation stories. They found that galaxies that stopped forming stars a long time ago had a higher density of dark matter in their centers than those that still form stars today. This supports the theory that the older galaxies heated less dark matter.

Justin Read is the lead author of the study and head of the Department of Physics at the University of Surrey. He said in a statement:

We found a truly remarkable relationship between the amount of dark matter in the centers of these little dwarfs and the amount of star formation they have experienced in their lives. The dark matter in the centers of the star-forming dwarfs seems to have been "heated up" and repressed.

The results represent a new limitation for dark matter models: dark matter must be able to form dwarf galaxies, which are an area of ​​central densities, and these densities must relate to the strength of star formation. Matthew Walker, a co-author of the study at Carnegie Mellon University, added:

This study could be evidence of smoking weapons that brings us one step closer to understanding dark matter. Our finding that it warms and moves motivates the search for particles of dark matter. Conclusion: New research indicates that dark matter can be heated and displaced by star formation in galaxies.

Source: Dark matter warms up in dwarf galaxies

Via Royal Astronomical Society

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