The objects, known as G3, G4, G5 and G6, could be gas clouds, according to some astronomers, but others believe they may be stars covered in dust. G1 was discovered by astronomer Andrea Ghez in 2005 and G2 was discovered in 2012 by German researchers.
“These objects look like gas and behave like stars,” said Ghez, one of the co-authors of the new research, in a statement.
In 2014, the German researchers spotted G2 making its way closer to the black hole, known as Sagittarius A*, leading Ghez and the others to believe it was likely two stars that were orbiting the black hole in conjunction with one another and eventually merged into a larger star, covered by a cloud of gas and dust.
“At the time of closest approach, G2 had a really strange signature,” Ghez added. “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.”
Mark Morris, a professor of physics and astronomy at UCLA and one of the study’s co-authors, said the mysterious “G objects” have excited researchers because of “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.”
“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,” Morris added.
It’s possible that all six G objects are binary stars (a two-star system orbiting each other) that are merging thanks to the strong gravitational force of Sagittarius A*, Ghez said, adding the process could take more than 1 million years to complete. This event is “quite common” throughout the universe, she pointed out.
“Black holes may be driving binary stars to merge,” Ghez continued. “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. We are learning how galaxies and black holes evolve. The way binary stars interact with each other and with the black hole is very different from how single stars interact with other single stars and with the black hole.”
The study’s lead author, Anna Ciurlo, said that even though the gas from G2’s outer shell was stretched, the dust inside the gas did not stretch, giving credence there is “a stellar object inside G2.”
“The unique dataset that Professor Ghez’s group has gathered during more than 20 years is what allowed us to make this discovery,” Ciurlo added. “We now have a population of ‘G’ objects, so it is not a matter of explaining a ‘one-time event’ like G2.”
The research has been published in the scientific journal Nature.
In May 2019, astronomers observed the sudden brightening of Sagittarius A*, suggesting it may have come in contact with another celestial object. Also known as Sgr A,* it has a mass 4 million times that of the sun and is 25,000 light-years from Earth.
In October 2018, astronomers observed Sgr A* pulling gas blobs into its vortex at 30 percent of the speed of light.