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Galaxies colliding
Mammoth Black Hole Hightailing it Outta There!
By Joshua Hill Saturday, May 3, 2008Galaxies weighing in at the size of our own Milky Way or larger are all presumed to harbor a supermassive black hole at their center. These monstrosities weigh millions or even billions of times as much as our own Sun.
Furthermore, when two of these sized galaxies collide, their respective black holes are thought to spiral in and collide, ie, merge.
These black hole mergers seriously mess with the surrounding space, sending out ripples in the fabric of space called gravitational waves. When shown in a computer simulation, these waves are seen to be emitted more in some directions than in others. As a result, the resulting merged black hole recoils in the opposite direction from the waves.
With speeds up to 4,000 kilometers per second, every now and then the recoil is enough to kick the new supermassive black hole right out of the merged galaxy.
Now, for the first time, astronomers have identified the first witnessed case of a supermassive black hole hightailing it out of its parent galaxies like a teenager with a trust fund out of his parent’s basement.
Stefanie Komossa of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, led the team that worked their way through observations of galaxies made by the Sloan Digital Sky Survey (SDDS). In the mass of observations they have found what they believe to be the signature of an ejected supermassive black hole, in the form of a quasar called SDSS J0927+2943.
According to Komossa’s team, the black hole looks to be speeding through its host galaxy. This speculation is based upon two sets of bright lines in the quasar’s light spectrum: one set appears to be from gas clouds within the galaxy, while the other looks to be matter closely orbiting a supermassive black hole.
Komossa and her team believe that the black hole is moving at 2650 kilometers a second, based on the way the lines appear to be shifted by the Doppler Effect (the Doppler Effect is the change in frequency and wavelength of a wave as perceived by an observer moving relative to the source of the waves).
However, never let it be said that science was a field without its naysayers. Avi Loeb of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, US, who authored a study on what signature is expected from a recoiling black hole, is not convinced of Komossa’s find.
Loeb, who spoke to New Scientist of his concerns, believes that the apparent shift of the bright lines associated with the galaxy gas clouds, could be due to the motion of those clouds within the galaxy itself, or possibly a distortion related to the clouds being unevenly illuminated.
“They need to provide more convincing evidence,” he said, but noting that if future observations show that the black hole is offset from the galaxy’s center, they would have a more convincing case.
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