July 30, 2013
Unraveling Galactic History Begins With A Black Hole’s Spin
Brett Smith for redOrbit.com - Your Universe Online
A supermassive black hole is believed to sit at the center of each large galaxy, and a new technique designed to detect the dark abyss' spin could be the key to unraveling a galaxy's history.
While black holes cannot be seen directly, their behavior can be determined by looking at how they affect nearby objects.
A paper published in Monthly Notices of the Royal Astronomical Society describes a new technique that was developed by researchers at Durham University in the UK, which is based on observations of a spiral galaxy 500 million light years from Earth. The galaxy's spiraling motion is driven by its central black hole's spin as it draws in interstellar gas and dust.
"If a black hole is spinning, it drags space and time with it, and that drags the accretion disk, containing the black hole's food, closer towards it," said study co-author Chris Done, an astrophysicist at the university. "This makes the black hole spin faster -- a bit like an ice skater doing a pirouette."
Using the European Space Agency's XMM-Newton satellite, the researchers were able to see the galaxy in the optical, ultra-violet and soft x-ray regions of the spectrum. They were also able to determine the accretion disk's distance from the black hole, thereby determining its rotation speed.
"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," Done said.
"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," she added. "This would be like something the size of a large boulder, influencing something the size of the Earth."
"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," Done concluded.
As a black hole feeds off its accretion disk, it also fires out superheated particles at high energies that keep intergalactic gases from coalescing into new stars in the outer galaxy. The Durham astrophysics team said they believe that these jets could be associated with the spin of the black hole.
Astrophysicists have been able to calculate the spin of black holes before. In February, another study from a different team calculated the rotation rate of the supermassive black hole anchoring the spiral galaxy NGC 1365. That team measured the distortions of high-energy light being emitted from the galaxy's accretion disk to calculate the gigantic black hole's spin.
Scientists have said that how a black hole consumes matter early on in a galaxy's existence can help to determine the accretion disk's rate of spin. If a black hole rapidly gulps down large quantities of matter, it will likely spin a galaxy at a higher rate. If a black hole ingests a moderate amount of material at a slow and steady rate, it will probably spin at a slower rate.