The elliptical galaxy M87 is known for a jet of radiation that is streaming from the supermassive black hole (SMBH) that the galaxy houses. This jet, which is visible through large-aperture telescopes, may have functioned as a black hole ‘jetpack’, moving the SMBH from the center of mass of the galaxy – where most SMBHs are thought to reside.
Observations taken with the Hubble Space Telescope by a collaboration of astronomy researchers at Rochester Institute of Technology, Florida Institute of Technology and University of Sussex in the United Kingdom show the SMBH in M87 to be displaced from the center of the galaxy by as much as 7 parsecs (22.82 light years). This contradicts the long-held theory that supermassive black holes reside at the center of the galaxies they inhabit, and may give astronomers one way to trace the history of galaxies that have grown through merging.
What caused M87’s SMBH to wander off so far from the center of the galaxy? The most likely cause is a merger between two smaller supermassive black holes sometime in the past. This merger could have created gravitational waves that gave the engorged black hole a swift kick. Elliptical galaxies like M87 are thought to become the size they are through the merger of smaller galaxies.
Another theory is that the jet of radiation that sprays out of the SMBH has pushed with enough energy to essentially propel the black hole away from the center of M87. Okay, so it’s not really a ‘black hole jetpack’, but you have to admit that the combination of black holes – which are cool – and jetpacks, also cool, is too good to pass up. The motion of the SMBH happens to be in the opposite direction of the jet that we can see streaming from the object. For this scenario to be true, however, the jet would have to have been much more energetic millions of years ago, the researchers concluded.
There also does exist evidence for another jet of material that is streaming out of the other side of the SMBH, which would cancel the pushing motion of the jet that we can see, making the merger scenario much more likely. If the two jets were asymmetric to a high degree, however, this scenario still may be the case. More information on the structure and history of the jets would better clarify the cause of the black hole’s displacement.
This study of M87 is part of a wider project aimed at constraining the placement of supermassive black holes, also known as Active Galactic Nuclei or quasars, in their home galaxies. David Axon, dean of mathematical and physical sciences at Sussex, said in a press release, “In current galaxy formation scenarios galaxies are thought to be assembled by a process of merging. We should therefore expect that binary black holes and post coalescence recoiling black holes, like that in M87, are very common in the cosmos.”
The displacement of such black holes would be apparent in archived Hubble Space Telescope images, and the researchers that discovered this phenomenon in M87 used the HST archives to pinpoint the location of the SMBH. Further analysis of these archives could yield many, many more ‘wandering’ black holes.
These findings were presented on May 25th at the American Astronomical Society meeting in Miami, Florida. The team of researchers that collaborated on the finding include Daniel Batcheldor and Eric Perlman of the Florida Institute of Technology, Andrew Robinson and David Merritt of the Rochester Institute of Technology and David Axon of the University of Sussex. Their results were accepted for publication in Astrophysical Journal Letters, and the original paper, A Displaced Supermassive Black Hole in M87, is available on Arxiv right here.