Mystery Objects Near Milky Way's Supermassive Black Hole Discovered

A group of mystery objects have been discovered near the supermassive black hole at the center of the Milky Way. These objects are huge, measuring around 100 AU—or 9.3 billion miles—and they appear to be interacting with the black hole, Sagittarius A* (Sgr A*), researchers say.

In total, researchers found six of these objects at the center of our galaxy. They have been named G1 to G6. The first, G1, was discovered in 2005 and the second, G2, was found in 2012. However, researchers led by Anna Ciurlo, from UCLA, have now found four more. Their findings have been published in Nature.

"The center of our galaxy is a complex and fascinating region," Ciurlo told Newsweek. "It hosts the closest supermassive black hole to us and so it provides a unique chance to look at the environment of a supermassive black hole. Initially, we were going to look at the effect of the black hole on the interstellar medium—gas clouds and clumps—around it. But then, these four compact objects caught our attention."

She continued: "We knew about G1 and G2 but we did not expect there to be a population of such objects. Since there are that many of these, it means that it's not just a rare chance event. There has to be a mechanism to form them."

What these objects are is unknown. However, the researchers say they look like gas but behave like a star. Their proximity to Sgr A* means that when they come near to it, the objects interact with it and are stretched along their orbit.

In 2014, G2 made a close approach to Sgr A*. At the time, scientists thought it might get swallowed, but it did not. Instead it was warped and elongated, before going back to its original shape after passing the black hole. This led to suggestions G2 was a large star cocooned in dust.

The discovery of four additional G objects may help scientists work out what these objects are.

Because they are not dragged into the black hole, researchers think they must be hiding a stellar object inside. The star's mass helps to keep the gas together and away from the black hole, Ciurlo explained. She added that had G2 been made up of just gas, it would have been swallowed by Sgr A*.

black hole objects
Diagram showing the orbits of the six G objects near to the supermassive black hole at the center of the Milky Way. Anna Ciurlo, Tuan Do/UCLA Galactic Center Group

"We believe these are what remains of the mergers of a pair of stars—a stellar core and dust and gas around it," she said. "We know that many stars form in pairs and we know that the presence of the black hole makes them merge more easily... This is not the only possible explanation, but it is the one that most nicely fits with what we know about this region."

In a statement, co-author Andrea Ghez said star mergers may be happening far more often than we think and that black holes may be driving these events. How black holes and galaxies evolve is not well understood. "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," she said.

"The Earth is in the suburbs compared to the center of the galaxy, which is some 26,000 light-years away. The center of our galaxy has a density of stars one billion times higher than our part of the galaxy. The gravitational pull is so much stronger. The magnetic fields are more extreme. The center of the galaxy is where extreme astrophysics occurs—the X Games of astrophysics."

Ciurlo said the team now plans to follow the G objects to better understand their orbits, including when they will next have a close encounter with Sgr A*. They will also look for more of these objects, in the Milky Way and beyond.