Astrophysicists detect light from behind a black hole for the very first-time confirming Einstein right, again
For the first time ever, scientists have detected light from behind a black hole, which was earlier thought to be impossible due to the supposed nature of Black Holes, but this discovery proves the elegant predictions seeded in Albert Einstein’s General Theory of Relativity.
We all know that a black hole is an astronomical object with a gravitational pull so strong that nothing, not even light, can escape it. A black hole’s surface called its event horizon, defines the boundary where the speed needed to escape exceeds the speed of light, which is the speed limit of the cosmos. Matter and radiation fall in, but they can’t get out.
Within the event horizon of a black hole space is curved to the point where all paths that light might take to exit the event horizon point back inside the event horizon. This is the reason why light cannot escape a black hole. Once a particle of light (‘photon’) passes the ‘event horizon’ of a black hole, it can no longer escape, but there’s nothing to suggest that it is destroyed. Like matter, the photon is rapidly sucked towards the singularity at the centre of the black hole, where a huge mass is packed into an infinitely small space.
Stanford University Astrophysicist Dan Wilkins and his colleagues were studying the X-rays flaring from a supermassive black hole in the center of the spiral galaxy named — Zwicky 1, 800 million light years away from us when they discovered the unexpected phenomenon. Aside from the anticipated X-ray flashes from the front of the black hole, the scientists additionally detected a number of ‘luminous echoes’ from an origin they at start couldn’t place. These additional flashes of X-rays were smaller, of different colors than the bright flares and arrived latter. According to the astrophysical theory, these luminous echoes were consistent with X-rays reflected from behind the black hole — but that creates a even bigger question — How can light from behind a black hole even be seen? Isn’t it strange if not impossible?
“Any light that goes into that black hole doesn’t come out, so we shouldn’t be able to see anything that’s behind the black hole,” said Wilkins, who is a research astrophysicist at the Kavli Institute for Particle Astrophysics and Cosmology at Stanford and SLAC National Accelerator Laboratory. It is another strange feature of the black hole, however, that makes this observation possible. “The reason we can see that is because that black hole is warping space, bending light and twisting magnetic fields around itself,” Wilkins explained. This odd discovery, detailed in a paper published July 28 in Nature, is the first direct observation of light from behind a black hole — a scenario that was predicted by Einstein’s General theory of Relativity but never confirmed, until now.
The real reason behind this research was to learn more about a mysterious characteristic of certain black holes, called a corona. Material falling into a supermassive black hole generates the brightest continuous sources of light in the universe, and as it does so, forms a corona around the black hole. This light — which is X-ray light — can be analyzed to map and characterize a black hole. The current theory for what a corona is starts with gas sliding into the black hole where it heats to millions of degrees. At that temperature, electrons separate from atoms, creating a magnetized plasma. Being stuck in the powerful rotational spin of the black hole, the magnetic field arcs so high above the black hole, and twirls about itself so much, that it eventually breaks altogether — a situation so close to what happens around our own Sun that it borrowed the name “corona.”
“This magnetic field getting tied up and then snapping close to the black hole heats everything around it and produces these high energy electrons that then go on to produce the X-rays,” said Wilkins.
As Wilkins took a closer look to investigate the origin of the flares, he saw a series of smaller flashes. These, the researchers determined, are the same X-ray flares but reflected from the back of the disk — a first glimpse at the far side of a black hole.
“I’ve been building theoretical predictions of how these echoes appear to us for a few years,” said Wilkins. “I’d already seen them in the theory I’ve been developing, so once I saw them in the telescope observations, I could figure out the connection.”
The echoes of X-rays from the disk have specific ‘colors’ of light and as the X-rays travel around the black hole, their colors change slightly. Because the X-ray echoes have different colors and are seen at different times, depending on where on the disk they reflected from, they contain a lot of information about what is happening around a black hole. The astronomers want to use this technique to create a 3D map of the black hole’s surroundings.
The mission to characterize and understand coronas continues and will require more observation. Part of that future will be the European Space Agency’s X-ray observatory, Athena (Advanced Telescope for High-Energy Astrophysics). As a member of the lab of Steve Allen, professor of physics at Stanford and of particle physics and astrophysics at SLAC, Wilkins is helping to develop part of the Wide Field Imager detector for Athena.
“It’s got a much bigger mirror than we’ve ever had on an X-ray telescope and it’s going to let us get higher resolution looks in much shorter observation times,” said Wilkins. “So, the picture we are starting to get from the data at the moment is going to become much clearer with these new observatories.”
Another mystery to be solved in future studies is how the corona produces such bright X-ray flares. The mission to characterize and understand black hole coronas will continue with XMM-Newton and ESA’s future X-ray observatory, Athena (Advanced Telescope for High-Energy Astrophysics).
The team published their findings in Nature. DOI: 10.1038/s41586–021–03667–0
Original Paper : https://arxiv.org/ftp/arxiv/papers/2107/2107.13555.pdf
