Sagittarius A (Sgr A), the supermassive black hole at the center of the Milky Way, is not quite active. It is not classified as an active galactic nucleus – one of those nuclei that glow extremely brightly as they absorb copious amounts of material from the surrounding space.
However, the brightness of the center of our galaxy fluctuates slightly every day across the entire electromagnetic spectrum. Astronomers have confirmed that Sgr A's most energetic X-ray flares have been increasing in the past few years.
This study has been accepted for publication in the journal Astronomy & Astrophysics and is now available on arXiv while the peer-review process is underway. The results support the findings of earlier studies that found our galactic center is indeed becoming restless.
In particular, a group of French and Belgian researchers led by astrophysicist Enmanuel Mossu of the University of Liege in Belgium continued work on a 2017 study, which found that the frequency of bright flares had tripled since August 31, 2014.
An earlier work – also co-authored with Mossu – examined X-ray data on Sgr A from the XMM-Newton, Chandra and Swift observatories, collected between 1999 and 2015. They found 107 flares. Not only have the brightest X-ray flares increased since August 2014, the faintest ones have decreased since August 2013.
To see if these trends have continued, Mossu and his colleagues collected and analyzed data from all three telescopes between 2016 and 2018. They found 14 more flares that can be added to the previous data for a total of 121.
They then analyzed all bursts of activity using previous methods and revised methods to determine the frequency of bursts and their distribution. They found that one of the earlier findings was wrong — there was no reduction in the rate of weak flares; they remained fairly stable throughout the data period.
“However, this did not change our global result: a change in the intensity of the flares was found for the brightest and most energetic flares on the same day as in the previous section,” the researchers write in their paper.
While both of these studies are only about X-rays, they are not the only hints that something is wrong with Sgr A. Last year, the black hole was 75 times brighter than normal near infrared brightness – the brightest we have ever seen. at these wavelengths.
A team that analyzed the near infrared observations and last year they found three nights when Sgr A activity in the near infrared was boosted. In their article, they stated that this is “unprecedented compared to historical data.”
Mossu and her team also tested whether the 2019 black hole activity was consistent with their recent findings. They analyzed data from the Swift Observatory for 2019 and found four bright flares, the largest number ever observed in a single observation session, confirming that the black hole is not settling down.
Observations at other wavelengths can provide more information as well. Continuous near infrared and radio wavelength observations can help us figure out what is causing Sgr A to 'wiggle'.
“Since 2014, the activity of Sgr A has increased by several wavelengths,” the researchers write.
“Additional multiwavelength data are needed to infer the persistence of this increase and to gain information about the source of this unprecedented supermassive black hole activity.”
The study is available on the arXiv website.
Sources: Photo: Sgr A. (NASA / CXC / MIT / F. Baganoff, R. Shcherbakov et al.)
