http://www.digitaljournal.com/article/268550

Scientists observe black holes in same galaxy

Posted Mar 5, 2009 by KJ Mullins
Scientists have seen two black holes dancing together in the same galaxy. It is believed that when galaxies are close together their black holes orbit each other until merging together.
Drawing of a massive star collapsing to form a black hole. Energy released as jets along the axis of...
Drawing of a massive star collapsing to form a black hole. Energy released as jets along the axis of rotation forms a gamma ray burst that lasts from a few milliseconds to minutes. Such an event within several thousand light years of Earth could disrupt the biosphere by wiping out half of the ozone layer, creating nitrogen dioxide and potentially cause a mass extinction.
Wikimedia Commons
The theory was published in the journal Nature. The work of astronomers at National Optical Astronomy Observatory in Arizona is detailed in the March 5 issue.
Xinhua reports:
The astronomers believe the two orbiting black holes eventually may merge into an even larger single black hole. "They should merge, and we expect them to," said study team member Tod Lauer.
Scientists believe that as matter falls into black holes it emits a characteristic colour that gives information about where the black hole is traveling. When two black holes orbit each other their colours are slightly different. This is the best evidence of "binary black hole system".
A pair of black holes exhibiting this behaviour has been spotted by Todd Boroson and Tod Lauer of the National Optical Astronomy Observatory. The pair has analysed 17,500 spectra from the Sloan Digital Sky Survey. The light sources that they have observed are 20 million and one billion times heavier than the Sun.
The Register reports:
NOAO elaborates: "The signature of a black hole in a galaxy has been known for many years. The material falling into a black hole emits light in narrow wavelength regions forming emission lines that can be seen when the light is dispersed into a spectrum.
"These emission lines carry the information about the speed and direction of the black hole and the material falling into it. If two black holes are present, they would orbit each other before merging and would have a characteristic dual signature in their emission lines. This signature has now been found."
Both of these black holes dwarf the Milky Way.
It is estimated that the quasar, known as SDSS J153636.22+044127.0, appears to host a pair of black holes orbit each other every 100 years.
BBC News reports:
"Previous work has identified potential examples of black holes on their way to merging, but the case presented by Boroson and Lauer is special because the pairing is tighter and the evidence much stronger," said Jon Miller, an astronomer at the University of Michigan.