Supermassive black holes are greedy. When clumps of dust and gas are drawn too close, they are easily disrupted by turbulence and radiation. So why are several of them orbiting the edge of the Milky Way’s supermassive monster, Sagittarius A*? Perhaps these mysterious clumps are hiding something.
An international team of researchers led by astrophysicist Florian Peisker of the University of Cologne analyzed observations of the dusty objects and found that these clumps could potentially harbor young stars (YSOs) shrouded in a haze of gas and dust. Even more strange, these infant stars are younger than an unusually young and luminous cluster of stars already known to orbit Sgr A*, known as an S star.
Stars orbiting supermassive black holes are thought to be fainter and much older, making it unusual for the two groups to orbit so close together. [these] They said they perceived the object as a coreless cloud in the high-energy radiation field of the supermassive black hole Sgr A*. study It was recently published in Astronomy and Astrophysics.
It’s not just space dust
To work out what the objects near Sgr A* might be, the researchers had to rule out those that weren’t: objects embedded in layers of gas and dust that maintain particularly high temperatures and don’t evaporate easily, and each orbits a supermassive black hole on its own.
The researchers were able to determine its chemical properties from the photons it emitted and found that its mid- and near-infrared emissions were consistent with those of a star. They used one of these objects, G2/DSO, as a case study to test their ideas about possible objects. This object is the easiest to study because of its high brightness and particularly strong emission. Its mass is also roughly the same as that of known low-mass stars.
YSOs are low-mass stars that have passed the protostellar stage but have not yet developed into main sequence stars, where hydrogen fuses into helium in their cores. These objects resemble YSO candidates because they cannot be clumps of gas and cosmic dust. A gas cloud with no gravitational force holding it inside cannot survive long in the close vicinity of a supermassive black hole. Its intense heat causes the gas and dust to evaporate quickly, and the thermally excited particles collide with each other and fly off into space.
The team calculated that a cloud the size of G2/DSO would evaporate in about seven years. A star orbiting the same distance from the supermassive black hole would not be destroyed as quickly, as it would be much denser and more massive.
Another type of object that dust clumps could hypothetically be, but aren’t in reality, are compact planetary nebulae (CPNs). These nebulae are the expanding outer gaseous layers of small to medium-sized stars in their death throes. CPNs share some characteristics with stars, but the strength of the gravity of a supermassive black hole causes the gaseous layers to easily separate and break apart.
And even though most stars form in binary systems, it’s unlikely that any YSOs are binary: SGR A*’s scorching temperatures and turbulence would likely cause stars that were once part of a binary system to move.
Stargazing
Further observations have revealed that some of the dusty objects are newborn stars, while others are thought to be stars of some kind but have not been definitively identified.
The properties that made G2/DSO an exceptional case study are also what identified it as a YSO: D2 is another luminous object with a mass similar to that of a low-mass star, and is easily observable in the near- and mid-infrared. D3 and D23 have similar properties; they are clumps close to a black hole that researchers believe are most likely YSOs.
There are other candidates that require further analysis. These include additional objects that show stellar characteristics but may or may not be YSOs, as well as the more difficult to observe objects D3.1 and D5. D9’s mid-infrared emission is particularly low compared to the other candidates, but it is thought to be some type of star, although it may not be a YSO. Objects X7 and X8 both exhibit the bow shock phenomenon, a shock wave caused by the stellar wind of one star pushing against the wind of another. It is unclear whether these objects are in fact YSOs.
It’s not clear where these dusty objects came from or how they formed. The researchers suggest that they formed together in molecular clouds falling towards the center of the galaxy. They also suggest that, regardless of where they were born, they traveled towards Sgr A* and that those that were in a binary system were separated by the black hole’s immense gravity.
Although it is unlikely that YSOs and potential YSOs originated in the same cluster as the slightly older S-type stars, they may be related in some way: they have undergone similar processes of formation and migration, and the young stars may eventually reach the same stage.
“Our guess is that the dust source will evolve into a low-mass S-type star,” Peisker’s team said in the same paper. study.
A black hole looks even more beautiful with a sparkling diamond necklace.
Astronomy and Astrophysics, 2024. DOI: 10.1051/0004-6361/202449729