The nature of a mystery cloud that survived a near encounter with a supermassive black hole has finally been revealed.
According to a recent study of the phenomenon, known as G2, it's really three young stars engulfed in a dense cloud of the gas and dust from which they were created. This explanation provides a neat response to the concerns that remained unanswered when G2 flew by Sgr A*, the supermassive black hole at the center of the Milky Way, in 2014.
"We propose that the monitored dust-enshrouded objects are remnants of a dissolved young stellar cluster whose formation was initiated in the circumnuclear disc," the researchers wrote in their paper.
In 2011, G2 was identified (described in a study published in 2012). It was speeding towards an event known as perinigricon — the point in its orbit when it was closest to the black hole.
Astronomers were fully expecting G2 to be ripped apart and slurped up by Sgr A*, resulting in some supermassive black hole feeding fireworks.
Nothing occurred, which was afterward referred to as a "cosmic fizzle." G2 extended and stretched as it approached the black hole, then recovered to a more compact form after perinigricon.
Another perplexing feature of G2 is that it is very hot, considerably hotter than a cloud of dust should be. It's conceivable that Sgr A* or other stars heated the object, but it stayed the same temperature regardless of where it was. This indicated that whatever was heating G2 was originating from inside the cloud itself, rather than from outside factors.
Astronomers discovered that both of these traits are more compatible with the activity of a star. Last year, a group of astronomers proposed that the G2 cloud may include a hidden star — the result of a collision between two stars that created a massive cloud of gas and dust around them.
However, the same study discovered four additional comparable objects near the galactic core, increasing the total number of G objects to six. That's a lot of binary stars merging together.
After completing a rigorous assessment of 14 years' worth of data obtained with the Very Large Telescope's SINFONI instrument, a team of researchers headed by astrophysicist Florian Peißker of the University of Cologne in Germany has come up with an alternate explanation.
According to their calculations, G2 should be hiding three stars that are roughly 1 million years old. That is extremely young for stars; the Sun is 4.6 billion years old. Because the G2 stars are so young, they are still surrounded by material from the cloud in which they originated.
"That G2 actually consists of three evolving young stars is sensational," Peißker says, noting that the discovery makes the three stars the youngest stars ever observed around SgrA*.
The S-cluster, an unusual collection of young stars, already exists in the galactic center. The G2 stars, according to Peißker's team's hypothesis, might be part of this population.
The stars might have formed a cluster in the same stellar nursery, which has now disintegrated, with individual stars breaking away and creating new orbits around Sgr A*.
Even if they were not members of the S-cluster, the G2 stars were most likely formerly part of a bigger cluster of stars. Other dusty objects circling Sgr A* might potentially have been part of this cluster, which would have been shattered by gravity after traveling a larger distance towards the supermassive black hole.
Because the environment near Sgr A* is not thought to be favorable for star formation, additional research will be required to determine where G2 and the other G objects may have originated. Astronomers may be able to utilize the new discoveries to learn more about black holes.
"The new results provide unique insights into how black holes work," Peißker says.
"We can use the environment of SgrA* as a blueprint to learn more about the evolution and processes of other galaxies in completely different corners of our Universe."
Reference(s): The Astrophysical Journal, University of Cologne
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