At the center of the Milky Way sits Sagittarius A*, a supermassive black hole that weighs 4.6 million times our Sun. It is orbited by several stars and a few peculiar objects including the mysterious X7. It’s possible X7 is not long for this world and could become food for Sagittarius A* within the next 15 years.
Astronomers have been studying the object, a suspected gas cloud, for a long time and have now shared observations of X7 spanning two decades. Its changing shape is an indication that it is not exactly solid; it is being altered by the gravity of the supermassive black hole. Now, they suspect it’s a debris cloud from a stellar collision.
X7 has a mass equivalent to about 50 Earths and is on an orbit around Sagittarius A* that takes about 170 years to complete. But the team believes that the cloud won’t be able to finish its orbit. In 2036, it will be at its closest point from the supermassive black hole, and it will likely be pulled in and eventually spiral toward it.
“We anticipate the strong tidal forces exerted by the galactic black hole will ultimately tear X7 apart before it completes even one orbit,” said co-author Mark Morris, UCLA professor of physics and astronomy, said in a statement.
At first, X7 was believed to be a G object. These are peculiar objects at the center of the galaxy that looks like gas clouds but behave like stars. But no G object has changed as much as X7 has.
“No other object in this region has shown such an extreme evolution,” lead author Anna Ciurlo, also of UCLA, said. “It started off comet-shaped and people thought maybe it got that shape from stellar winds or jets of particles from the black hole. But as we followed it for 20 years we saw it becoming more elongated. Something must have put this cloud on its particular path with its particular orientation.”
But there are few possibilities about where X7 comes from.
“One possibility is that X7’s gas and dust were ejected at the moment when two stars merged,” Ciurlo explained. “In this process, the merged star is hidden inside a shell of dust and gas, which might fit the description of the G objects. And the ejected gas perhaps produced X7-like objects.”
“This is a very messy process: The stars circle each other, get closer, merge, and the new star is hidden within a cloud of dust and gas. X7 could be the dust and gas ejected from a merged star that’s still out there somewhere.”
Another explanation is that the cloud is associated with a young star S50 and that the cloud comes from it and is responding to the peculiar environment around the supermassive black hole.
The findings are reported in The Astrophysical Journal.
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