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How does dark matter influence the size of a black hole? That’s the question a group of researchers are trying to answer in a new study.
Every massive galaxy has a black hole in its center. Scientists have assumed the mass of the central black hole was linked to the total mass of stars in elliptical galaxies. But, more recent studies have suggested a link between the mass of the black hole and the galaxy’s dark-matter.
“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,” says lead author Akos Bogdan of the Harvard-Smithsonian Center for Astrophysics.
Dark matter has long eluded scientists. We know it’s out there based on its gravitational effects. It holds our galaxy together and outweighs normal matter (everything we see) 6 to 1.
Bogdan and his colleague Andy Goulding (Princeton University) observed these gravitational effects as they studied more than 3,000 elliptical galaxies. Specifically, they used star motions to help weigh each galaxy’s central black hole. X-ray measurements were taken of hot gas surrounding these galaxies. The more dark matter a galaxy has, the more hot gas it can have.
The researchers used data from the Sloan Digital Sky Survey and the ROSAT X-ray satellite’s all-sky survey.
Their findings support those of more recent studies. They found a stronger relationship between the mass of the dark-matter halo and the mass of the black hole – compared to the number of stars in the galaxy and the black hole.
According to the researchers, this relationship is likely due to how elliptical galaxies form. These galaxies form when two smaller galaxies merge. Since dark matter outweighs all other matter significantly, it shapes this new elliptical galaxy and influences the growth of the central black hole.
Bogdan explains, “In effect, the act of merging creates a gravitational blueprint that the galaxy, the stars and the black hole will follow in order to build themselves.”