A new way of measuring the spin in supermassive black holes, reported in a paper in the Monthly Notices of the Royal Astronomical Society (full paper in .pdf), could lead to better understanding about how they drive the growth of galaxies.
This artist’s concept depicts a supermassive black hole at the center of a galaxy (NASA / JPL-Caltech)
To test the new method, astrophysicists at Durham University observed a black hole with mass 10 million times that of our Sun at the center of a spiral galaxy known as PG1244+026 about 500 million light years from Earth while it was feeding on the surrounding disc of material that fuels its growth and powers its activity. By viewing optical, ultra-violet and soft x-rays generated by heat as the black hole fed, they were able to measure how far the disc was from the black hole.
This distance depends on black hole spin as a fast spinning black hole pulls the disc in closer to itself. Using the distance between the black hole and the disc, the scientists were able to estimate the spin of the black hole.
Understanding spin could lead to greater understanding of galaxy growth over billions of years.
Black holes lie at the centers of almost all galaxies, and can spit out incredibly hot particles at high energies that prevent intergalactic gases from cooling and forming new stars in the outer galaxy. Scientists don’t yet understand why the jets are ejected into space, but the Durham team believes that their power could be linked to the spin of the black hole.
Spin is difficult to measure as it only affects the behavior of material really close to the black hole.
“We know the black hole in the center of each galaxy is linked to the galaxy as a whole, which is strange because black holes are tiny in relation to the size of a galaxy. This would be like something the size of a large boulder, influencing something the size of the Earth,” explained first author Prof Chris Done.
“Understanding this connection between stars in a galaxy and the growth of a black hole, and vice-versa, is key to understanding how galaxies form throughout cosmic time.
“If a black hole is spinning it drags space and time with it and that drags the accretion disc, containing the black hole’s food, closer towards it. This makes the black hole spin faster, a bit like an ice skater doing a pirouette.
“By being able to measure the distance between the black hole and the accretion disc, we believe we can more effectively measure the spin of black holes. Because of this, we hope to be able to understand more about the link between black holes and their galaxies.”
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Bibliographic information: Chris Done et al. A new way to measure supermassive black hole spin in accretion disc-dominated active galaxies. MNRAS, published online July 29, 2013; doi: 10.1093/mnras/stt1138
