Nature gets very, very weird when this happens, but it’s nowhere near Earth. So being able to watch it, even from tens of thousands of light-years away, is like having a front-row seat to the cutting edge of human knowledge. That’s why astronomers aimed an instrument called Gravity at Sagittarius A*. In uncomplicated terms, Gravity combines the light harvested by four telescopes, each with a 30-foot diameter, in the VLT array in Chile, operated by the European Southern Observatory.
Gravity does so as a super-precise, super-cooled instrument that allows researchers to extract more information from the incoming light, turning the array into one very powerful virtual telescope equivalent to 425 feet in diameter. This extra resolving power helped astronomers peer at a plane of gas and dust falling toward Sagittarius A*, a feature called an accretion disk.
The disk is about 100 million miles wide, or a little wider than Earth is distant from the sun. The Gravity tool helped the team look for flares of infrared light, which astronomers had seen for more than a decade. But this time, with incredible resolving power, they tried to stare at the innermost edge of the disk.
During observations on the nights of May 27, July 22, and July 28, Gravity saw three flares, one after another, in a clockwise pattern. The data suggested the flares came from a blob of hot gas circling the black hole.
“As a cloud of gas gets closer to the black hole, they speed up and heat up,” Peters said. “It glows brighter the faster and hotter it gets. Eventually, the gas cloud gets close enough that the pull of the black hole stretches it into a thin arc.”
This happened just outside the event horizon, in an area that astronomers refer to as a physical point of no return, called the “innermost stable circular orbit” or ISCO, a region not yet observed before.
Move a blob of matter closer than the ISCO, the thinking goes, and it can’t escape. The gravity of a black hole will accelerate the blob of matter, giving it more energy, which will, as Einstein’s work explains, give it a stronger gravitational force. This then pulls it faster toward the black hole, creating a feedback loop of relativistic physics that ends in oblivion.
What the edge of our supermassive black hole might look like
The event observed by astronomers is shown in the ESO’s image at the top of this story, though it’s not a photograph, but a visual simulation that uses data collected by Gravity and other telescopes.
Orange shows what researchers think is the blob of superheated gas, or plasma, while blue shows radiation that bleeds off the matter and occasionally bursts into bright flares. The image also illustrates the bending and distortion of light caused by the black hole warping space-time with its concentrated mass, an effect called gravitational lensing.
ESO also created an animation of the gas cloud and flares:
The flares were seen on Earth in infrared light, which is just out of the range of human visibility. But infrared wasn’t the only form of flare radiation.
“If you were close enough to observe these flares, you’d be in a lot of trouble,” Tana Joseph, an astrophysicist and fellow at the University of Manchester who wasn’t involved in the study, told Business Insider in an email. “We would see extremely bright flashes of optical light, and there would be lots of high-energy radiation, like gamma rays and X-rays, that would be very damaging to our bodies.”
Peters said flares had been seen coming from Sagittarius A* before. But she added that the new observations, showing the very edge of the black hole, were like going from the resolution of an old television to a high-definition flat-screen TV.
A flashing space-time lens?
What causes these flares is an active mystery. One idea is that extreme forces around the black hole — primarily intense magnetic fields — will occasionally toss off and accelerate some of the hot plasma into jets, which then bleed off energy as flares.
“We see plasma flares associated with magnetic fields in many places, including our own sun, but we don’t yet fully understand the exact causes of such flares,” Misty Bentz, an astrophysicist at Georgia State University who also wasn’t part of the study, told Business Insider in an email.
But something far weirder may be at play: large distortions in space-time caused by the spinning of a black hole at some fraction of the speed of light. Such distortions might be focusing the energy bleeding off orbiting blobs of hot plasma into a beam, which occasionally flashes across the telescopes of Earth, creating a flare.
“The black hole is like this lighthouse lens that’s causing this thing to flash at us as it goes around,” Avery Broderick, an astrophysicist at the Perimeter Institute of Theoretical Physics and the University of Waterloo, told Quanta Magazine. (Broderick first proposed this idea in 2005.)
The ESO’s press release says the flares “provide long-awaited confirmation that the object in the center of our galaxy is, as has long been assumed, a supermassive black hole.”
This claim is most likely overblown, however, since it’s virtually impossible to directly confirm the existence of a black hole, short of visiting one or “listening” to them crash together.
“One might argue that you can never prove the existence of an invisible object like a black hole,” Bentz said. “But this new study with Gravity confirms that a compact object with a mass of 4 million suns is still the only way to explain all the observations.”
Bentz is eager to know what the flares foretell. She also described the very circular orbit of the blob of plasma as unusual. This may suggest that the rotational axis of Sagittarius A*, like a tilting spinning top, wasaligned with the Milky Way a few million years ago but has inexplicably pointed toward Earth.