An elongated dust and gas feature named X7 has a mass of about 50 Earth masses and is on an orbital path around Sagittarius A*, the supermassive black hole at the center of our Milky Way Galaxy, that would take 170 years to complete.
Morphology evolution of X7’s thermal dust emission between 2002 and 2021: the images are oriented with equatorial north at the top and with Sagittarius A* positioned in the upper left corner of each panel. Image credit: Ciurlo et al., doi: 10.3847/1538-4357/acb344.
“No other object in this region has shown such an extreme evolution,” said Dr. Anna Ciurlo, an astronomer in the Department of Physics and Astronomy at the University of California, Los Angeles.
“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.”
X7 has a mass of about 50 Earths and is on an orbital path around Sagittarius A* that would take 170 years to complete.
But that might never happen. Based on its trajectory, Dr. Ciurlo and colleagues estimates that the object will make its closest approach to the supermassive black hole around the year 2036, and then likely spiral toward it and disappear.
“We anticipate the strong tidal forces exerted by the Galactic black hole will ultimately tear X7 apart before it completes even one orbit,” said University of California, Los Angeles Professor Mark Morris.
“Tidal forces are the gravitational pull that cause an object approaching a black hole to stretch; the side of the object closest to the black hole is pulled much more strongly than the opposite end.”
X7 shows some of the same properties as the other strange dusty objects orbiting Sagittarius A*.
Those so-called G-objects look like gas but behave like stars.
But X7’s shape and velocity have changed more dramatically than G-objects have.
As it accelerates toward the black hole, X7 is moving rapidly, clocking in at speeds of up to around 1,130 km per second (700 miles per second).
“It’s exciting to see significant changes of X7’s shape and dynamics in such great detail over a relatively short time scale as the gravitational forces of the supermassive black hole at the center of the Milky Way influences this object,” said Dr. Randy Campbell, an astronomer at the W.M. Keck Observatory.
Although X7’s origin is still the subject of debate, the finding suggests that it arose after two stars collided.
“One possibility is that X7’s gas and dust were ejected at the moment when two stars merged,” Dr. Ciurlo said.
“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.”
“The merger of two stars is very common, especially when they are near black holes.”
“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.”
A paper on the findings was published in the Astrophysical Journal.