In 2020, researchers discovered six objects around Sagittarius A* that are unlike anything in the galaxy. The region of a supermassive black hole is already a fairly strange location. They are so unusual that astronomers have given them a brand-new class they are calling G objects.

Nearly two decades ago, the initial two objects, G1 and G2, first drew the attention of astronomers. Over the following years, their orbits and peculiar characteristics were progressively pieced together. They seemed to be enormous gas clouds that were 100 astronomical units wide, growing larger as they moved closer to the black hole and emitting spectra of gas and dust.

G1 and G2, however, weren’t acting like gas clouds.

According to physicist and astronomer Andrea Ghez of the University of California, Los Angeles, “These objects look like gas but behave like stars,” in 2020.

For more than 20 years, Ghez and her colleagues have been researching the galactic centre. The UCLA astronomer Anna Ciurlo and her team used that information to identify four further examples of these objects, designated G3, G4, G5, and G6.

weird orbits

They follow radically different orbits than G1 and G2 (seen above), and their combined orbital durations span from 170 to 1,600 years.

Although G2’s unbroken exit from periapsis in 2014, when it was at its closest point in its orbit to the black hole, was a significant indication, according to Ghez, it is still unclear exactly what they are.


“G2 had a really strange signature at the time of closest approach,” she stated.

“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 most of its gas was shattered. It was a fairly harmless thing when it was far from the black hole, but as it got close, it was greatly stretched out and twisted and lost its outer shell. Now it’s starting to grow more compact again.

Before, it was believed that G2 was a hydrogen gas cloud that Sgr A* was going to gobble up and consume, creating some supermassive black hole accretion pyrotechnics. It was afterwards referred to as a “cosmic fizzle” that nothing occurred.

The researchers think that large binary stars hold the key to finding the solution. The most of the time, these twin stars, which are in a shared orbit, merely hang around and act like buddies. But occasionally, exactly like two binary black holes meeting, they can squish together and merge into a single large star.


When this occurs, a huge cloud of gas and dust is created, which surrounds the newly formed star for almost a million years following the collision.


Ciurlo said, “Something must have maintained [G2] compact and allowed it to survive its encounter with the black hole.” This is proof that there is a star object inside of G2.

What about the other five, then? They may also be binary star mergers, though. The majority of the big stars at the galactic centre are binary stars. Additionally, the strong gravitational forces at work around Sgr A* may be sufficient to periodically disrupt their binary orbits.


Star mergers are probably fairly common in the universe and may occur more frequently than we previously assumed.




Binary star mergers may be triggered by black holes. It’s likely that many of the stars we’ve been observing and finding difficult to explain are the result of mergers that are at peace right now. We are finding out how black holes and galaxies develop. The interactions between binary stars and the black hole are substantially different from those between single stars and other single stars, as well as from those between single stars and the black hole.


Whatever they are, the G objects do appear to have a lot in common, and increasing the dataset will only add more details to help solve the enigma. However, there is still plenty to learn. like some unexplained explosions that have been seen flashing out of Sgr A*.

Was that the periapsis of G2’s delayed response? Was the cosmic fizzle actually not all that fizzly? To find out what happens next, we may have to keep an eye on this odd small supermassive black hole region in space.


The study was released in Nature.

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