A researcher at Saint Mary’s University in Halifax was part of a team of scientists that observed light coming from behind a black hole for the very first time, confirming a prediction from famous physicist Albert Einstein’s theory of general relativity.
While scientists have seen X-ray emissions around black holes before, it’s the first time light has been spotted behind a black hole – and the new discovery could lead to a better understanding of what’s still largely considered to be an astronomical mystery.
Luigi Gallo, a professor of astronomy at Saint Mary’s University who’s been studying black holes for 20 years, worked on the data analysis and interpretation for this research project, led by Stanford University astrophysicist Dan Wilkins.
“They’re my favourite objects, but I think I’m biased a bit,” Gallo said of black holes. “It’s the most extreme object in space, right? We don’t know a lot about them.”
Gallo’s research focuses on supermassive black holes – the regions in space where gravity is so strong that not even light can escape. Supermassive black holes are 10 million times larger than the sun.
Because of their very nature, black holes themselves can’t be seen. Scientists are only able to observe the objects around them.
As materials in space fall into a black hole, they form what’s called an “accretion disk,” where they spiral around before falling into the black hole.
On top of a black hole is a primary light source known as a “corona,” which illuminates the material. When the light shines onto the accretion disk, it bounces off and creates X-ray emissions or flares.
“It’s not exactly like a reflection in a mirror. What happens is that light comes back with different colours and it comes back at different times,” Gallo explained.
Proving Einstein right
What the five-person research team observed was a big flare coming from a supermassive black hole in a galaxy 800 million light-years away known as I Zwicky 1, using two space-based X-ray telescopes from NASA and the European Space Agency.
Shortly after seeing the big flare, Gallo said they observed a smaller flare in a different colour – an “echo” of the first flare.
“We were able to interpret that as light coming from the other side of the black hole,” said Gallo. “Which is really kind of cool, we haven’t ever been able to isolate exactly where light is coming from on the accretion disk … but in this instance, we’re actually able to say, ‘Oh, this light is coming from behind the black hole.’”
That echo could be seen because the black hole was warping space by bending light around itself. Thus, Einstein’s century-old prediction was proven right, Gallo said.
“This is basically confirming how the space-time around a supermassive black hole is shaped,” he said.
“That’s why we can see light coming from behind the black hole, it’s because it’s taken this curved path around the black hole and landing now on us, so that we can see it … Because space is bent, which is a prediction of general relativity, we’re able to see what’s behind the black hole.”
This research, published earlier this week in Nature, opens the door a little further for scientists studying black holes.
Gallo said it will allow them to eventually draw a 3D picture of what the region around the supermassive black hole looks like. As well, he said they will continue to study “coronas” to better understand them, which was actually the driving motivation behind this discovery.
Gallo took note of the “incremental” nature of science and said there are decades of other discoveries that led them to this point.
“The telescopes that we work on get better and better with time, and the techniques that we develop get better and better,” he said.
“The discovery made today … is based on decades of work of many, many other scientists that brought us here.”
He added that it’s important to study black holes, since their formation and evolution is “tightly linked” to the formation and evolution of galaxies.
“Galaxies are stars, and then the stars are forming planets, and planets are where we are,” he said. “All this is kind of tied in understanding the origins of where we come from.
“So it is an important field of research, but it’s fun. So it’s kind of easy for me to justify doing this kind of work.”
— With a file from The Canadian Press