Researchers have identified four more of these strange objects that look like gas clouds but behave like stars.
By Bruno Carbinatto
16 Jan 2020, 5:19 pm
In the center of the Milky Way, about 26,000 light-years away from Earth, is a supermassive black hole called Sagittarius A * that swallows anything that dares to get too close. But this galactic monster is not alone in the heart of our galaxy – a series of foreign bodies, dubbed "G-objects," have been detected by astronomers in recent years, and the discovery of four such objects was confirmed last Thursday. (16), in a study published in the journal Nature.
But there is a problem. No one really knows what these objects really are: they look like clouds of gas, but they behave like stars.
G1, the first object of its kind, was discovered in 2005 and already displayed ambiguous characteristics. A few years later, in 2012, a team of German astronomers discovered the G2, which proved to be an even bigger puzzle: in 2014, it got too close to the Sagittarius A * black hole, but contrary to what was expected, the object did not was destroyed. The G2 suffered only deformations, losing its outermost part to the black hole and maintaining a compact remnant. This behavior looks more like a star orbiting the black hole than a cloud of gas – which makes its exact nature a great mystery.
The newest four G-objects, named G3 through G6, were identified by the team of Anna Ciurlo, an astronomer at the University of California, Los Angeles. The discovery comes after 13 years of analyzing data about the center of the Milky Way collected at the W.M.Keck Observatory in Hawaii.
Initially, the researcher sought to study the influence of Sagittarius A * on the surrounding gas, but, on the way, came across these dense and strange bodies. Newly discovered objects appear compact most of the time, undergoing slight deformation as they approach the black hole – following the pattern of others already detected.
There is, however, an important difference between them: While the orbits of G1 and G2 relative to the center of the Milky Way are relatively similar, those of the new objects vary significantly. This may be an indication that, even though they belong to the same “group”, the objects can have different origins – or at least influence factors -.
The mystery continues
Although no one knows for sure what they are, there are some good guesses. One is that G-objects are the result of the fusion of binary stars – systems formed by two stars orbiting a common center of mass. According to the team in the new study, these stars may have fused due to the enormous gravitational pull of Sagittarius A *, in a process that lasted millions of years and resulted in a single star surrounded by a large layer of gas and dust. This would explain their conflicting appearance and behavior. When these objects approach the black hole, that outer layer would be destroyed, but the inner star object would remain intact.
"Star fusions may be happening in the universe more often than we thought and are probably quite common," said Andrea Ghez, professor of astronomy at the University of California at Los Angeles and co-author of the new study. “Black holes may be causing binary stars to merge. It is possible that many of the stars that we observe and cannot understand may be the end product of these mergers. ”
Another hypothesis is that the objects are just very compacted gas clouds, formed by the extreme events that frequently occur in the center of our galaxy, with enough resistance to face the black hole without being totally destroyed. One piece of evidence that seems to support this idea is that, despite the seemingly stellar behavior, no light has been detected in the bodies.
In addition to the four new G-objects, the team announced that it is studying other candidates that could be included in the group. If confirmed, they will offer more opportunities for observations (and research) that may reveal new details about the strange nature of these hybrids.