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Black hole in the center of the Milky Way is unpredictable and chaotic – mysterious flares erupt every day

Super massive black hole artist concept illustration

The artist's concept illustration of a supermassive black hole emitting an X-ray. Credit: NASA / JPL-Caltech

An international team of researchers, led by postgraduate student Alexis Andrés, has found that black hole at the center of our galaxy, Sagittarius A *, flares not only irregularly from day to day, but also in the long run. The team analyzed 15 years 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 announcements from the Royal Astronomical Society.

Sagittarius A * is a powerful source of radio, X-rays and gamma rays (visible light is blocked by intermediate gas and dust). Astronomers have known for decades that Sagittarius A * flashes every day and emits radiation eruptions that are ten to a hundred times brighter than normal signals observed from the black hole.

X-ray image of Sagittarius A *

This X-ray image of the galactic center fuses all Swift observations from 2006 to 2013. Sagittarius A * is in the center. Low energy (300 to 1,500 electron volts) X-rays look red. Green is medium energy (1,500 to 3,000 eV). Blue is high energy (3,000 to 10,000 eV). Credit: NASA / Swift / N. Degenaar

To find out more about these mysterious eruptions, the team of astronomers, led by Andrés, searched for patterns in 15 years of data provided by NASA's Neil Gehrels Swift Observatory, a satellite in orbit around the Earth dedicated to detecting gamma-ray bursts. Swift Observatory has been observing gamma rays from black holes since 2006. Analysis of the data showed high activity levels from 2006 to 2008 with a sharp decline in activity over the next four years. After 2012, the frequency of flares increased again - researchers had difficulty distinguishing a pattern.

Over the next few years, the team of astronomers expects to collect enough data to rule out whether the variations in Sagittarius A * burnouts are due to passing gaseous clouds or stars, or whether something else may explain the observed irregular activity from our galaxy's central black hole.

"The long data set from the Swift Observatory did not just happen by accident," says co-author and former supervisor of 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 have applied for more observation time regularly. It is a very special observation program that allows us to do a lot of research. ”

Co-author Dr. Jakob van den Eijnden, or the University of Oxford, comments on the team's results: "How exactly the flare-up occurs is still unclear. It was previously thought that more eruptions follow gaseous clouds or stars pass the black hole, but there is no evidence for that yet. And we can not yet confirm the hypothesis of , that the magnetic properties of the surrounding gas also play a role. ”

Reference: "A Swift study of long-term changes in the X-ray burning properties of Sagittarius A "by A Andrés, J van den Eijnden, N Degenaar, PA Evans, K Chatterjee, M Reynolds, JM Miller, J Kennea, R Wijnands, S Markoff, D Altamirano, CO Heinke, A Bahramian and G Ponti, D Haggard, December 9, 2021, Monthly announcements from the Royal Astronomical Society.
DOI: 10.1093 / mnras / stab3407

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