Mysterious Dark Matter Guides the Growth of Supermassive Black Holes in Galaxies

It turns out that dark matter may be responsible for guiding the growth of supermassive black holes. Every massive galaxy has a black hole at its center and the larger that galaxy, the bigger its black hole. Now, scientists have taken a closer look at why the two are related.

"There seems to be a mysterious link between the amount of dark matter a galaxy holds and the size of its central black hole, even though the two operate on vastly different scales," said Akos Bogdan, the lead author of the new study, in a news release.

Previous observations have found a relationship between the mass of the central black hole and the total mass of stars in elliptical galaxies. However, more recent studies have suggested a tight correlation between the masses of the black hole and the galaxy's dark matter halo. In order to see which relationship dominated, the researchers examined ellipticals a bit more closely.

The scientists studied more than 3,000 elliptical galaxies. They used star motions as a tracer to weight the galaxies' central black holes. X-ray measurements of hot gas surrounding the galaxies helped weight the dark matter halo, because the more dark matter a galaxy has, the more hot gas it can hold onto.

In our universe, dark matter outweighs normal matter by a factor of six to one. We know that dark matters exists only from its gravitational effects of holding together galaxy and galaxy clusters. Every galaxy is surrounded by a halo of dark matter that weights as much as a trillion suns and extends for hundreds of thousands of light-years.

In the end, the researchers found a distinct relationship between the mass of the dark matter halo and the black hole mass. This relationship was stronger than that between a black hole and the galaxy's stars alone.

This connection is likely related to how elliptical galaxies grow. Elliptical galaxies are formed when smaller galaxies merge and their dark matter and stars mingle. Because dark matter outweighs everything else, it molds the newly formed elliptical galaxy and guides the growth of the central black hole.

The findings are published in The Astrophysical Journal.

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