Three new dusty stellar objects — so-called ‘G-type’ objects — have been spotted at the center of our Milky Way Galaxy.
This 3D spectro-imaging data cube was produced using software called OsrsVol, short for OSIRIS-Volume Display; Ciurlo et al developed this custom volume rendering tool to separate G3, G4, and G5 from the background emission; once the 3D analysis was performed, the astronomers could clearly distinguish the G-objects, which allowed them to follow their movement and see how they behave around the supermassive black hole. Image credit: Ciurlo et al.
First discovered in the early 2000s, G-objects look like gas clouds, but behave like stars; they move extremely fast and close to the Milky Way’s supermassive black hole, Sagittarius A*.
A G-object named G1 was first seen in 2004, and G2 was discovered in 2012. Both were thought to be gas clouds until they made their closest approach to the supermassive black hole.
G1 and G2 somehow managed to survive the black hole’s gravitational pull, which can shred gas clouds apart.
“If they were gas clouds, G1 and G2 would not have been able to stay intact,” said Professor Mark Morris, from the University of California, Los Angeles.
The three newfound objects — dubbed G3, G4, and G5 — share the physical characteristics of G1 and G2.
Professor Morris and colleagues made their discovery by obtaining spectroscopic measurements of the Galactic Center’s gas dynamics using Keck Observatory’s OH-Suppressing Infrared Imaging Spectrograph (OSIRIS).
“Our view of the G-objects is that they are bloated stars — stars that have become so large that the tidal forces exerted by Sagittarius A* can pull matter off of their stellar atmospheres when the stars get close enough, but have a stellar core with enough mass to remain intact,” Professor Morris said.
The question is then, why are they so large? It appears that a lot of energy was dumped into the G-objects, causing them to swell up and grow larger than typical stars.
“We think that these G-objects are the result of stellar mergers — where two stars orbiting each other, known as binaries, crash into each other due to the gravitational influence of the giant black hole,” the astronomers said.
“Over a long period of time, the black hole’s gravity alters the binary stars’ orbits until the duo collides. The combined object that results from this violent merger could explain where the excess energy came from.”
“In the aftermath of such a merger, the resulting single object would be ‘puffed up,’ or distended, for a rather long period of time, perhaps a million years, before it settles down and appears like a normal-sized star.”
“If these objects are indeed binary star systems that have been driven to merge through their interaction with the central supermassive black hole, this may provide us with insight into a process which may be responsible for the recently discovered stellar mass black hole mergers that have been detected through gravitational waves,” said Dr. Andrea Ghez, from the University of California, Los Angeles.
“Understanding G-objects can teach us a lot about the Galactic Center’s fascinating and still mysterious environment. There are so many things going on that every localized process can help explain how this extreme, exotic environment works,” added Dr. Anna Ciurlo, also from the University of California, Los Angeles.
The astronomers presented their findings June 7, 2018 at the 232nd Meeting of the American Astronomical Society in Denver, Colorado.
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Anna Ciurlo et al. 2018. Keck Observations of the Gas Dynamics at the Galactic Center. 232nd Meeting of the American Astronomical Society, abstract # 402.05
