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Dark matter heats up and moves around in dwarf galaxies during star formation

The exact nature of dark matter is one of the enduring questions of physics, as it is difficult to identify and has many mysterious manifestations. Now a team from the University of Surrey, U.K., has discovered that dark matter can be heated up and can move around a galaxy due to star formation.

The scientists looked for evidence of dark matter by examining the centers of nearby dwarf galaxies — small and faint galaxies which usually orbit around larger galaxies like the Milky Way that we live in. The challenge of finding dark matter is that is does not interact with light in the way that other matter does, so the only way in which it can be spotted is by inferring its presence from its gravitational effects.

The team took the approach of studying the effects of star formation in dwarf galaxies. When a star forms, it can generate strong solar winds which carry gases and dust particles away from the center of the galaxy and toward its edges. This means that over time there is less mass at the heart of the galaxy, which affects its gravity. We know that dark matter tends to cluster in the center of galaxies, so when dwarf galaxies lose mass from their centers, scientists are able to see how the change in gravity effects the remaining dark matter. The research found that in these situations, the dark matter gained energy and also moved away from the center of the galaxy in a process that scientists have called “dark matter heating.”

They looked at dark matter at the center of sixteen different dwarf galaxies which had a variety of different histories of star formation. They found that galaxies which had stopped forming stars many years ago had a higher density of dark matter in their centers than galaxies which were still forming stars today. “We found a truly remarkable relationship between the amount of dark matter at the centers of these tiny dwarfs, and the amount of star formation they have experienced over their lives,” Professor Justin Read, lead author of the study and Head of the Department of Physics at the University of Surrey, said in a statement. “The dark matter at the centers of the star-forming dwarfs appears to have been ‘heated up’ and pushed out.”

On the left, the image shows the hydrogen gas density of a simulated dwarf galaxy as seen from above. On the right, data from a real dwarf galaxy, IC 1613, is shown. Dark matter responds to the flow of gases away from the center of the galaxy and towards the edges by also moving away from the center of the galaxy. J. Read et al., University of Surrey

The new research is published in Monthly Notices of the Royal Astronomical Society.

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