G2, a celestial object discovered by scientists in 2003 and believed to be a cloud of hydrogen gas, had a close encounter with a supermassive black hole at the center of the Milky Way earlier this year.
This is a phenomenon that astronomers were excited about because this would allow them to witness the giant gas cloud being gobbled up by the black hole called Sagittarius A*.
Contrary to what astronomers expected, though, G2 was not destroyed during its close approach with the black hole, and a new study offers a plausible explanation why.
For their research published in the journal Astrophysical Journal Letters on Nov. 3, Andrea Ghez from the department of physics and astronomy at the University of California Los Angeles (UCLA), and colleagues said that the reason G2 proceeded unscathed after its encounter with the black hole is that it is not actually a cloud of hydrogen gas at all.
If G2 had been a hydrogen gas cloud as it was initially believed, astronomers assumed that it could have been torn apart by Sagittarius A*, which would have produced celestial fireworks.
"G2 survived and continued happily on its orbit; a simple gas cloud would not have done that," Ghez said. "G2 was basically unaffected by the black hole. There were no fireworks."
After conducting a detailed study of G2 using the world's largest optical and infrared telescopes at the W.M. Keck Observatory in Hawaii, the researchers proposed that G2 is likely to be a pair of stars. The researchers acknowledged that had it not been for Keck's technology, their detailed observations would not have been made possible.
Ghez and colleagues determined that the binary star system had been orbiting the black hole together and then merged to become an extremely large star enveloped in dust and gas with its movement being influenced by the powerful gravitational field of the black hole.
The researchers likewise noted that G2 appeared to be one of an emerging class of stars close to the black hole, which were created due to the powerful gravity of the black hole causing the binary stars to merge into one.
"G2 is a dusty red object associated with gas that shows tidal interactions as it nears its closest approach with the Galaxy's central black hole," the researchers wrote. "We suggest that G2 is a binary star merger product and will ultimately appear similar to the B-stars that are tightly clustered around the black hole (the so-called S-star cluster)."
