Black hole pairs destined
DR EMILY BALDWIN
Posted: 13 January 2011
New research has spotted 16 pairs of close-knit black holes cruising for a collision as their host galaxies merge, the largest population of such objects found as a result of a systematic search.
The black holes are separated by just a few thousand light years, a hundred to a thousand times closer together than the black hole pairs that have been observed before. S. George Djorgovski, who presented the results at the American Astronomical Society meeting this week, points out that even though thousands of light years may seem like a large separation, "the galaxies themselves are in a serious interaction when some tens of kiloparsecs apart, or even higher."
Examples of some of the newly discovered double active nuclei. On the left are traditional astronomical "seeing limited" images from the Sloan Digital Sky Survey (SDSS); the central box is shown expanded on the right, as observed with the Keck telescope and Adaptive Optics. (In some images there is a further zoom-in on the central portion, shown in the upper right.) Image: S. G. Djorgovski, H. Fu, et al., Caltech.
“This is a very nice confirmation of theoretical predictions,” he says. “These close pairs are a missing link between the wide binary systems seen previously and the merging black-hole pairs at even smaller separations that we believe must be there.”
The observations were enabled thanks to the Laser Guide Star Adaptive Optics system at the W. M. Keck Observatory on Mauna Kea, which removes the blurring effect of Earth's atmosphere to allow sharper images to be obtained. The galactic targets were selected from the Sloan Digital Sky Survey, but in these images the galaxies are unresolved, so the astronomers identified black hole pairs that displayed double sets of emission lines in their spectra, a classic signature of two active nuclei.
Galaxy mergers have played an important role in the evolution of the Universe, combining forces to make larger galaxies. All galaxies are thought to host a black hole in their core, which are also destined to combine during a merging event. These dramatic collisions are expected to generate gravitational waves, which are yet to be detected, but the new discovery of close active nuclei is one step closer to learning the effects of such an event.
Djorgovski tells Astronomy Now that the black hole pairs identified in this new study will collide on the order of millions of years, and that the future generation of telescopes such as the Thirty Metre Telescope (TMT) will help astronomers search for black hole binaries that are even closer together.
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