Astronomers Unfold Mystery About G2 Cloud Near Black Hole

Astronomers at UCLA have unfolded a mystery about a bizarre object in the center of the Milky Way that was discovered by Lawrence Livermore National Laboratory  and once believed to be a hydrogen gas cloud that was on its way to galaxy’s enormous black hole (to be fed on).

The astronomers identified the object, designated G2 , during its closest approach to the black hole this summer, and found the black hole did not feed on it. Previously, it was believed to be cloud of dust and gas and known as G2 cloud.

According to Andrea Ghez, professor of physics and astronomy in the UCLA College, G2 is most likely a pair of binary stars that had been orbiting black hole one behind the other which later got merged together, cloaked in gas and dust, and choreographed by the black hole’s powerful gravitational field.

Some scientists believed G2 was a cloud of hydrogen gas that could have been torn apart by the black hole and the state of the black hole would have changed due to the resulting celestial fireworks, but Ghez resisted that it wasn’t just a simple cloud of gas. G2 survived as its gravity remained uninterrupted and continued to stay on its orbit. A simple gas cloud would not have done that and there were no fireworks.

“Black holes, which form out of the collapse of matter, have such high density that nothing can escape their gravitational pull — not even light. They cannot be seen directly, but their influence on nearby stars is visible and provides a signature,” said Ghez.

She conjectured that G2 appears to be just one of an emerging class of stars near the black hole that are created because of the black hole’s powerful gravity that drives binary stars that once moved in tandem to merge into one. She also noted that, in our galaxy, massive stars primarily come in pairs. She says the star suffered an abrasion to its outer layer but otherwise will be fine.

“G2 is not alone,” said Ghez. “We’re seeing a new class of stars near the black hole, and as a consequence of the black hole.”

Ghez determined that G2 appears to be in an inflated stage now; and at the same time, is now undergoing “spaghetti-fication” — a phenomenon in which large objects become elongated and rip apart by gravitational forces on falling into a black hole.

Also, the gas at G2’s surface is being heated by stars around it, creating an enormous cloud of gas and dust that has shrouded most of the massive star.

“We are seeing phenomena about black holes that you can’t watch anywhere else in the universe,” Ghez added. “We are starting to understand the physics of black holes in a way that has never been possible before, and is possible only at the center of the galaxy.”

The research was conducted at Hawaii’s W.M. Keck Observatory, home of two largest optical and infrared telescopes in the world. It was published in the journal Astrophysical Journal Letters.

• Reference: Detection of Galactic Center Source G2 at 3.8 μm during Periapse Passage
• Sources: W.M. Keck Observatory, UCLA
• Image: ESA, Ethan Tweedie