UCLA-Led Team Solves The Mystery Of The Astronomical Object G2

Chuck Bednar for redOrbit.com – Your Universe Online

An unusual object located at the center of the Milky Way is most likely not a hydrogen gas cloud headed towards the galaxy’s black hole, but a pair of binary stars that had been orbiting it together before merging into a single, extremely large star, researchers from the UCLA Department of Physics and Astronomy have discovered.

Writing in Monday’s edition of Astrophysical Journal Letters, UCLA physics and astronomy professor Andrea Ghez and her colleagues reached the conclusion after studying the object, known as G2, during its closest approach to the black hole this summer. Their observations, they said, were designed to test the theory that G2 was a gas cloud with a mass of approximately three Earth masses.

In actuality, the authors determined that the movement of the now-combined binary stars was choreographed by the black hole’s powerful gravitational field. Had it been a hydrogen cloud, they noted, it likely would have been torn apart by the black hole, and the resulting “celestial fireworks” would have had a dramatic impact on the black hole, which was formed out of the collapse of matter and is so dense that nothing can escape its gravitational pull.

“G2 survived and continued happily on its orbit; a simple gas cloud would not have done that,” Professor Ghez, who is also the Lauren B. Leichtman and Arthur E. Levine Chair in Astrophysics at UCLA and a 2008 MacArthur Fellow, explained in a statement Monday. “G2 was basically unaffected by the black hole. There were no fireworks.”

Black holes cannot be observed directly, as not even light can escape their gravity, but their influence on nearby stars can be used to analyze them, according to the researchers. Ghez, who has studied thousands of stars in the neighborhood of the supermassive black hole, said that G2 appears to be one of an emerging class of stars located near the black hole that are created because the powerful gravity causes binary stars to merge into one.

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The professor noted that massive stars found in the Milky Way typically come in pairs, and that the star at the center of the new study suffered an abrasion to its outer layer but should be fine on the whole. The research was conducted at the W.M. Keck Observatory in Hawaii, which is home to the world’s two largest optical and infrared telescopes.

When two binary stars near the black hole combine, the resulting star continues to expand for more than a period of one million years before settling back down, Ghez explained. She noted that this phenomenon “may be happening more than we thought. The stars at the center of the galaxy are massive and mostly binaries. It’s possible that many of the stars we’ve been watching and not understanding may be the end product of mergers that are calm now.”

Based on their observations, the team behind this new study determined that G2 appears to currently be in the inflated stage, and is undergoing something Ghez refers to as “spaghetti-fication,” a phenomenon that takes place near black holes in which large objects become elongated. In addition, the gas at G2’s surface is being heated by surrounding stars, creating a massive cloud of gas and dust that has enveloped most of the massive star.

The researchers said they would have been unable to successfully complete their research without the 10-meter telescopes at the Keck Observatory, which use adaptive optics in order to correct the distorting effects of the Earth’s atmosphere and give the astronomers a better look at the space surrounding the supermassive black hole.

“We are seeing phenomena about black holes that you can’t watch anywhere else in the universe. We are starting to understand the physics of black holes in a way that has never been possible before,” Ghez explained. The research was funded by the National Science Foundation (NSF), the Lauren Leichtman and Arthur Levine Chair in Astrophysics, the Preston Family Graduate Student Fellowship and the Janet Marott Student Travel Awards.

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