During the 232nd American Astronomical Society Meeting, a team of researchers led by Anna Ciurlo of UCLA presented the results of a research on what were called G-objects. They look like dust clouds but act like stars and move very fast in the area around the supermassive black hole at the center of the Milky Way. Using data collected over the past 12 years by the Keck Observatory in Hawaii, the researchers concluded that these are bloated stars, so large that the black hole steal their materials from them.
The supermassive black hole at the center of the Milky Way, Sagittarius A* or simply Sgr A*, has an estimated mass of around 4 million solar masses. The area around it is chaotic, subject to huge gravitational forces but is far from empty. For example, there are stars so fast that they’re influenced by the effects predicted by Albert Einstein’s theory of general relativity. There are also stranger objects, for example in 2004 the first of the ones called G-objects was discovered and today a team of researchers has offered an explanation for their nature.
In 2012 another G-object was discovered and at that point the two were called respectively G1 and G2. The strange characteristics, in part like dust clouds and in part like stars, raised perplexity among astronomers. The discussions between various teams that conducted research on them went on but two objects were perhaps not enough to obtain a final answer.
Analyzing the data collected in the last 12 years using the Keck Observatory’s OH-Suppressing Infrared Imaging Spectrograph (OSIRIS) instrument, the team led by Anna Ciurlo discovered three more G-objects, called G3, G4 and G5. The image (courtesy Keck Observatory. All rights reserved) shows a 3D representation of the data collected with the OSIRIS spectrograph using a software called OsrsVol (OSIRIS-Volume Display).
The software was developed to separate G3, G4 and G5 from background emissions and allow to follow their movements and behaviors in their motion around Sagittarius A*. The analysis of the data led to the conclusion that they’re bloated stars that have become so large that the tidal forces exerted by Sagittarius A* can steal materials from their atmosphere when they approach the black hole. However, they have a stellar nucleus with enough mass to remain intact.
The researchers wondered why these stars are so big that they can be mistaken for dust clouds. One hypothesis is that they’re the result of mergers of stars that originally formed binary systems. Normally in these cases the two companions orbit each other but the gravitational interference of Sagittarius A* may have destabilized that balance. The energy generated by the merger could have bloated those stars.
For now that’s a hypothesis and further studies will be needed to understand if it’s the correct one. The observations will be particularly interesting when the G-objects will be at their closest to Sagittarius A* but this will happen over the next few decades. There’s plenty of time to conduct a lot of research, also with the next generation instruments, to study the Milky Way’s most extreme area.