The forces generated by Sagittarius A* (Sgr A*), the supermassive black hole at the center of our own Milky Way, appear to have formed a new class of celestial objects.
In results published in the journal Nature by researchers from UCLA's Galactic Center Orbits Initiative, the team describes how the objects — termed "G objects" — behave like stars but appear as blobs of gas. Over the course of their orbits, which range from 100 to 1,000 years, the six observed objects remain compact, but then dramatically stretch as they approach the black hole.
"At the time of closest approach, G2 had a really strange signature," co-author Andrea Ghez, UCLA professor of astrophysics and director of the Galactic Center Group, said in a statement. "We had seen it before, but it didn't look too peculiar until it got close to the black hole and became elongated, and much of its gas was torn apart. It went from being a pretty innocuous object when it was far from the black hole to one that was really stretched out and distorted at its closest approach and lost its outer shell, and now it's getting more compact again."
A stellar merger
The plotted orbits of the six G objects around Sgr A*. (Photo: Anna Ciurlo, Tuan Do/UCLA Galactic Center Group)
Based on 13 years of data collected from observations by the Keck Observatory on Maunakea in Hawaii, Ghez and her team believe the strange objects were likely originally binary stars (stars that closely orbit each other), but violently merged due to the strong gravitational forces of the black hole.
The findings are exciting, not only because it's likely these mergers are happening near every supermassive black hole, but because they may also help explain other odd objects that have puzzled researchers.
"Mergers of stars may be happening in the universe more often than we thought, and likely are quite common," Ghez said. "Black holes may be driving binary stars to merge. 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."
According to co-author Mark Morris, UCLA professor of physics and astronomy, the most visually interesting part of this whole mystery may be yet to come.
"One of the things that has gotten everyone excited about the G objects is that the stuff that gets pulled off of them by tidal forces as they sweep by the central black hole must inevitably fall into the black hole," Morris said. "When that happens, it might be able to produce an impressive fireworks show since the material eaten by the black hole will heat up and emit copious radiation before it disappears across the event horizon."