UA Researcher Helps Identify Massive Black Hole, Tidal Disruption

TUSCALOOSA, Ala. — Astronomers have predicted big black holes sit at the center of all galaxies. A University of Alabama professor contributed to a study finding one such black hole a million times as massive as our sun in the midst of eating a large star with a mass twice that of our sun.

The researchers found a multi-wavelength flare from a tidal disruption in a dwarf starburst galaxy – a galaxy that can be seen as generating a large number of stars. The galaxy, some 1.8 billion light years from Earth, features a large star that’s being consumed – the tidal disruption event – by a black hole, said Dr. Jimmy Irwin, associate professor of physics and astronomy.

“If a star gets too close, a black hole will rip it apart,” Irwin said. “When it gets ripped apart, some of the material gets thrown out into the galaxy, while the rest of the material begins to orbit the black hole. As the material circles the black hole, it generates a lot of heat, and it generates a strong X-ray signature. Several dozen of these events have been found to date– but most take about a year to subside, because the majority of the material is eaten by the black hole and is no longer visible.”

The tidal disruption event in this particular galaxy has been observed for more than 11 years, Irwin said. Researchers conclude a large black hole in the middle of this galaxy is causing the event. This discovery tends to support the long-held astronomic conjecture that a big black hole sits in the middle of most galaxies. Black holes are by definition hard to see – they don’t give off enough energy, and most galaxies are too far away to observe star movement around them.

“One thing the discovery tells us is that there’s a black hole there,” Irwin said. “It’s too far away to determine its existence by the motion of the stars around the center. We believe every galaxy has a black hole, but we don’t usually don’t see it. These X-ray flares are the only clues we have that a massive black hole is in the center of a galaxy.”

Irwin said the rate of X-ray emission from the event suggests the material coming from the star will decrease, and the event will fade over the next few years.

The researchers used data from a trio of orbiting X-ray telescopes, NASA’s Chandra X-ray Observatory and Swift Satellite as well as ESA’s XMM-Newton. The lead author, Dr. Dacheng Lin works at the University of New Hampshire and is a former UA post-doctorate researcher with whom Irwin has collaborated. For more information on the discovery, go to https://phys.org/news/2017-02-black-hole-frenzy.html.