Our Milky Way galaxy hosts a supermassive black hole- named Sagittarius A*- at its center. For years, astronomers have known that Sagittarius A* flashes every day. It emits bursts of radiation ten to a hundred times brighter than normal signals observed from the black hole.
After analyzing 15 years’ worth of data, an international team of scientists found that the black hole not only flares irregularly from day to day but also in the long term.
The team analyzed data gathered by NASA’s Neil Gehrels Swift Observatory. Analysis revealed high levels of activity from 2006 to 2008. There was a sharp decline in activity observed in the next four years. After 2012, the frequency of flares increased again- making it difficult for scientists to distinguish a pattern.
Scientists are looking forward to obtaining enough data to rule out whether the variations in the flares from Sagittarius A* are due to passing gaseous clouds or stars or whether something else can explain the irregular activity observed from our galaxy’s central black hole.
Dr. Nathalie Degenaar, also at the University of Amsterdam, said, “The long dataset of the Swift observatory did not just happen by accident. Since then, I’ve been applying for more observing time regularly. It’s a very special observing programme that allows us to conduct a lot of research.”
Co-author Dr. Jakob van den Eijnden of the University of Oxford comments on the team’s findings: “How the flares occur exactly remains unclear. It was previously thought that more flares follow after gaseous clouds or stars pass by the black hole, but there is no evidence for that yet. And we cannot yet confirm the hypothesis that the magnetic properties of the surrounding gas play a role either.”
- A Andres et al. A Swift study of long-term changes in the X-ray flaring properties of Sagittarius A. DOI: 10.1093/mnras/stab3407