Our galaxy’s black hole went through ‘unprecedented’ changes and left scientists baffled as it suddenly grew 75 times brighter than normal.
In comparison to an active nucleus which spews out light and heat, Sagittarius A*, the supermassive black hole at the heart of the Milky Way, is quite calm, typically displaying minimal fluctuations in its brightness.
Sgr A* is the closest black hole we can see, located 26,000 light-years from Earth, and on May 13 scientists observing it with the Keck Telescope on the summit of Mauna Kea in Hawaii observed it growing 75 times brighter in the near-infrared band of the light spectrum.
The team managed to capture the scene in a time-lapse, with two hours condensed down to a few seconds:
Here's a timelapse of images over 2.5 hr from May from @keckobservatory of the supermassive black hole Sgr A*. The black hole is always variable, but this was the brightest we've seen in the infrared so far. It was probably even brighter before we started observing that night! pic.twitter.com/MwXioZ7twV
— Tuan Do (@quantumpenguin) August 11, 2019
UCLA astronomer Tuan Do, who was one of the astronomers observing the black hole, told ScienceAlert at first he didn’t even know what he was looking at.
The scientist explained:
I was pretty surprised at first and then very excited.
The black hole was so bright I at first mistook it for the star S0-2, because I had never seen Sgr A* that bright. Over the next few frames, though, it was clear the source was variable and had to be the black hole. I knew almost right away there was probably something interesting going on with the black hole.
Taken when I was @keckobservatory, this raw image shows the brightest Sgr A* has ever been observed in the infrared (center). The emission associated with the black hole also changed by a factor of 75 over that night. Is Sgr A* waking up? Will we finally see 🎆? pic.twitter.com/lX7ZO2PhX2
— Tuan Do (@quantumpenguin) August 8, 2019
In a forthcoming study set to be published in The Astrophysical Journal Letters, Do explains the Milky Way’s supermassive black hole ‘reached much brighter flux levels in 2019 than ever measured at near-infrared wavelengths’.
The study explains the unusually bright flux levels and variability showed peaks ‘twice the maximum historical flux measurements’ – meaning the next-brightest flare was only twice as bright as this one.
The scientists aren’t sure exactly what caused the black hole to suddenly light up but the team are gathering data in an attempt to figure it out.
According to ScienceAlert, black holes themselves don’t emit radiation which we can detect but the surroundings do when the black hole’s gravitational forces generate immense friction, which produces radiation.
The brightness variations come from the light of hot gas falling towards the black hole, before it crosses the event horizon. The black hole itself doesn't emit light. Increased activity is probably related to changes in the gas flow. Big questions: why? how long will this last?
— Tuan Do (@quantumpenguin) August 14, 2019
The radiation translates as brightness when we view it with a telescope so when the surroundings of a black hole flare like they did on May 13 it’s a sign something may have come close enough to be grabbed by its gravity.
One possibility is an object thought to be a gas cloud, known as G2, which approached within 36 light-hours of Sagittarius A* in 2014. If it is a gas cloud the proximity should have torn the object apart, but nothing happened. However, scientists have suggested the recent sudden brightness was a delayed reaction.
Another possibility is the star S0-2, which is on a 16-year elliptical orbit around Sgr A* and last year made its closest approach.
One of the possibilities is that the star S0-2, when it passed close to the black hole last year, changed the way gas flows into the black hole and so more gas is falling on it, leading it to become more variable.
Astronomers will continue to observe the supermassive black hole in the coming weeks to gather more data and the team are currently awaiting results from other telescopes which have been observing Sgr A* in the last few months.
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Emily Brown first began delivering important news stories aged just 13, when she launched her career with a paper round. She graduated with a BA Hons in English Language in the Media from Lancaster University, and went on to become a freelance writer and blogger. Emily contributed to The Sunday Times Travel Magazine and Student Problems before becoming a journalist at UNILAD, where she works on breaking news as well as longer form features.