New Class Of Strange Objects Discovered Orbiting The Milky Way’s Supermassive Black Hole

Sagittarius A*, a supermassive black hole that weighs more than 4.6 million times as much as our Sun, is located at the centre of the Milky Way. Stars and gas are located everywhere around it. Now, astronomers from UCLA and the W. M. Keck Observatory have discovered an additional object: strange objects that belong to a distinct class.

In 2005, the first object of this new "G" class was found. In 2012, G2, a second one, was discovered. A recent Nature research has now shown the existence of four more. It is thought that the objects are the result of a stellar merger. The resulting large star has a thick gas envelope that spreads out like an interstellar gas cloud as it approaches the black hole.

According to co-author Professor Andrea Ghez, director of the UCLA Galactic Center Group, "These things appear like gas yet behave like stars."

Ghez observed that G2 had an extremely peculiar signature at the moment of closest approach. "We'd seen it before, but until it got close to the black hole, it didn't seem particularly strange. It then grew longer and much of its gas was shattered. It was a fairly harmless object when it was far from the black hole, but when it got close, it was really stretched out and distorted and lost its outer shell. Now it's starting to get more compact again.

The team hypothesises that Sagittarius A* may have been instrumental in promoting mergers of this nature. While the gas was stretched during the close approach to the black hole, the team found that the dusty component within the gas was not, which gives them confidence that the G objects are stars.

It must have been maintained compact in order for it to survive its collision with the black hole. This supports the existence of a stellar object inside G2, according to lead author and UCLA postdoctoral researcher Anna Ciurlo.

We were able to make this discovery thanks to the special dataset that Professor Ghez's team has amassed over the course of more than 20 years, she continued. It is not necessary to explain a "one-time event" like G2 because there is now a population of "G" objects.

The six G objects' orbits around the supermassive black hole take between 100 and 1,000 years to complete. It's possible that the activity observed in 2019 is related to the gas that G2 lost during its close approach in 2014 finally reaching Sagittarius A*. 

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