Double-Nucleus Galaxies More Common than Thought

A Cauldron of Stars at the Galaxy's Center: the central white patch in the image is the dense star cluster at the center of our galaxy
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Established astronomical knowledge had it that galaxies with two nuclei were very rare. Experts believed that small galaxies had one made up of a star cluster, whereas the more massive ones had a black hole at their cores. But a new study comes to prove that the double-nucleus galaxy is, in fact, not that rare of an occurrence. In the research, which analyzed 50 regular galaxies, 12 were found to have both a black hole and a star cluster at their cores. A paper detailing the finds appears in the latest issue of the scientific journal Monthly Notices of the Royal Astronomical Society, ScienceDaily reports.

In charge of the new investigation were Swinburne University of Technology (SUT) Associate Professor Alister Graham and Dr. Lee Spitler. Much to their amazement, they discovered that it was not at all uncommon for regular galaxies to have a black hole at their cores, as well as a cluster containing up to ten million stars around them. The presence of such a significant number of double-nucleus galaxies increases the chance of some peculiar astronomical phenomena occurring, Graham reveals. One example consists of black holes beginning to consume nearby stars.

“When stars get too close to massive black holes, the gravitational attraction is such that they can be devoured. When you’ve got up to a million stars within the immediate vicinity of a black hole, the chance of this occurring increases significantly,” the expert says. He adds that such proximity could mean that there are also more hyper-velocity stars in existence than first estimated. “This is when a star approaches a massive black hole and gets caught in a gravitational slingshot. When this happens stars can be ejected from galaxies at speeds in excess of 500 kilometers per second,” Graham explains.

The team also says that double-nucleus galaxies increase chances that the phenomenon known as gravitational radiation actually exists. “Such emission has been predicted by Einstein’s General Theory of Relativity, but has never been observed. It is theorized that when stars spiral quickly around a black hole the motion will create gravitational waves – causing ripples in the space-time continuum,” Spitler shares.

“As part of our study we were able to look at star clusters and black holes and determine their mass in proportion to each other and their host galaxies. This knowledge is going to affect the way astronomers develop models for galaxy formation and evolution. Previously evolution models only dealt with one type of nucleus per galaxy. We now have the rationale and data to develop hybrid models that can account for co-existing nuclei and hopefully explore their dynamic joint evolution,” Graham concludes.