Black holes in galaxy cores related to spiral arms

Giant black holes are thought to reside in the cores of many galaxies, including our own Milky Way. Astronomer Marc Seigar has looked at several dozen galaxies, to study the relationship between the possible mass of these central black holes and the appearance of the galaxies’ spiral arms.

Marc Seigar: What we found is that the mass of black holes, or supermassive black holes at the centers of spiral galaxies is related to how tightly wound the spiral arms are in the galaxy.

Because of this relationship, Seigar said, the shape of a galaxy’s spiral arms can be used to measure the mass of possible gargantuan black hole at the cores of distant galaxies.

Marc Seigar: As the material moving around the center of the black hole moves faster and faster, that would also indicate a more massive black hole.

Seigar’s 2008 study involved 27 galaxies – including the galaxy we live in, the Milky Way.

Marc Seigar: The mass of the black hole in the Milky Way is about three million times the mass of the sun. And the spiral arm of the Milky Way, there’s a pitch angle that’s been measured, so the Milky Way falls very nicely on the relationship that we see.

He said invisible dark matter might be driving the spiral arm/black hole relationship.

Marc Seigar: So the visible galaxy that we see is sitting at the center of a huge dark matter halo. And the distribution of mass in that halo, or even the total mass of the halo itself, might be affecting how big the central supermassive black hole is, and how tightly wound the spiral structure is.

Our thanks to:
Marc S. Seigar
Department of Physics and Astronomy
University of Arkansas at Little Rock

February 27, 2009

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