The First Pair of Supermassive Black Holes Discovered In An Ordinary Galaxy

Images: ESA - C. Carreau & ESA - A. Read (University of Leicester).

For the first time, at the center of an inactive galaxy astrophysicists have discovered a pair of supermassive black holes. The distinctive objects were revealed because they ripped apart a star when the ESA's telescope just occurred to be viewing in the right direction. Maximum massive galaxies (including Milky Way galaxy) are believed to port at least one supermassive black hole at their center. Till now, only a few candidates have been discovered, and all of them have been in active galaxies where they’re tearing gas clouds apart, a harsh procedure that heats up gas so much that it shines at numerous wavelengths. They’re considered “active” because of the resultant bright center.

This recently discovered binary supermassive black hole, by a worldwide team directed by Fukun Liu of Peking University, is not in an active galaxy, but in an “inactive” one. A very first of its kind. The discovery was distributed in the Astrophysical Journal this week.

 According to the study, co-author Stefanie Komossa from Max-Planck-Institut für Radioastronomie, the entire populations of inactive galaxies might be hosting binary black holes in their center. But finding them is hard as inactive galaxies have no gas clouds to uninterruptedly nourish black holes, which leaves these galaxies’ centers dark. Black holes in inactive galaxies are nourished by “tidal disruption events” that happen intermittently. That’s after the gravity of a black hole tears a star into parts, giving out a burst of X-rays.

The European Space Agency's X-ray Multi-Mirror Mission (XMM-Newton) was plotting the sky in a random arrangement when, on 10 June 2010, it detected a tidal distraction event in the galaxy SDSS J120136.02+300305.5. Many days later, the galaxy was still leaking X-rays into space.

Then something strange occurred: The X-rays fell below measureable levels between days 27 and 48 after the detection. But then they returned and continued to track a more predictable dying rate, as if nothing had occurred. "This is exactly what you would expect from a pair of supermassive black holes orbiting one another," Liu explains in a news release.

Liu’s representations of black hole binary systems projected an unexpected drop to darkness, followed by a retrieval. The gravity of one black hole can momentarily deprive the other of its fuel to emit X-ray flares.

He measured two imaginable configurations: one with an elliptical orbit and the other with a circular one. In both circumstances, the black holes were only parted by 0.6 milliparsecs, or about 2 thousandths of a light year. Being this near means they’ll finally spiral together, and in about two million years, they’ll combine into a single black hole.
Binary black holes can tell astronomers about how galaxies grew into their current shapes and sizes. “The final merger is expected to be the strongest source of gravitational waves in the Universe," Liu says. Here, is the X-ray swing tracks recorded by XMM-Newton from over 1200 characters recorded between 2001 and 2012.

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