An international team of researchers, led by postgraduate student Alexis Andrés, has found that the black holeA black hole is a place in space where the pull of gravity is so strong not even light can escape it. Astronomers classify black holes into three categories by size: miniature, stellar, and supermassive black holes. Miniature black holes could have a mass smaller than our Sun and supermassive black holes could have a mass equivalent to billions of our Sun.”>black hole at the center of our galaxy, Sagittarius A*, not only flares irregularly from day to day but also in the long term. The team analyzed 15 years’ worth of data to come to this conclusion. The research was initiated by Andres in 2019 when he was a summer student at the University of Amsterdam. In the years that followed, he continued his research, which is now to be published in Monthly Notices of the Royal Astronomical Society.
Sagittarius A* is a strong source of radio, X-rays, and gamma rays (visible light is blocked by intervening gas and dust). Astronomers have known for decades that Sagittarius A* flashes every day, emitting bursts of radiation that are ten to a hundred times brighter than normal signals observed from the black hole.
To find out more about these mysterious flares, the team of astronomers, led by Andrés, searched for patterns in 15 years of data made available by NASAEstablished in 1958, the National Aeronautics and Space Administration (NASA) is an independent agency of the United States Federal Government that succeeded the National Advisory Committee for Aeronautics (NACA). It is responsible for the civilian space program, as well as aeronautics and aerospace research. It’s vision is “To discover and expand knowledge for the benefit of humanity.””>NASA’s Neil Gehrels Swift Observatory, an Earth-orbiting satellite dedicated to the detection of gamma-ray bursts. The Swift Observatory has been observing gamma rays from black hole since 2006. Analysis of the data showed high levels of activity from 2006 to 2008, with a sharp decline in activity for the next four years. After 2012, the frequency of flares increased again — the researchers had a difficult time distinguishing a pattern.
In the next few years, the team of astronomers expect to gather enough data to be able 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.
“The long dataset of the Swift observatory did not just happen by accident,” says co-author and previous supervisor to Andrés, Dr. Nathalie Degenaar, also at the University of Amsterdam. Her request for these specific measurements from the Swift satellite was granted while she was a PhD student. “Since then, I’ve been applying for more observing time regularly. It’s a very special observing program that allows us to conduct a lot of research.”
Co-author Dr. Jakob van den Eijnden, of the University of OxfordThe University of Oxford is a collegiate research university in Oxford, England that is made up of 39 constituent colleges, and a range of academic departments, which are organized into four divisions. It was established circa 1096, making it the oldest university in the English-speaking world and the world’s second-oldest university in continuous operation after the University of Bologna.”>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.”
Reference: “A Swift study of long-term changes in the X-ray flaring properties of Sagittarius A” by A Andrés, J van den Eijnden, N Degenaar, P A Evans, K Chatterjee, M Reynolds, J M Miller, J Kennea, R Wijnands, S Markoff, D Altamirano, C O Heinke, A Bahramian and G Ponti, D Haggard, 9 December 2021, Monthly Notices of the Royal Astronomical Society.