Black holes are notoriously dark objects, but now Stanford astronomers have spotted some strange light coming from behind one. The X-ray echoes seem to be the result of the intense gravity of the object warping space and bending the light back around into view.
Famously, the gravitational pull of a black hole is so powerful that not even light itself can escape. That of course makes these strange objects invisible – but they can reveal themselves from the light they produce around them.
As black holes slurp up dust and gas, the intense energy heats that material up to incredible temperatures, creating a highly magnetized plasma that glows brightly. A black hole can then be seen as a circular silhouette against this bright disc.
Sometimes, X-ray flashes can be seen emanating from the disc. In the extreme environment around the black hole, the plasma’s magnetic field can twist and arc all over the place, eventually snapping and producing high-energy electrons. These in turn give off X-ray flares.
In the new study, astronomers started out by investigating the cause of these X-rays, around a supermassive black hole some 800 million light-years away. In doing so, they noticed something new – smaller flashes of X-rays occasionally followed the main ones, at different wavelengths. According to models, these later flashes were the same X-ray flares being reflected from the back of the disc, marking the first time astronomers have seen light from the far side of a black hole.
“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,” says Dan Wilkins, an author of the study. “The reason we can see that is because that black hole is warping space, bending light and twisting magnetic fields around itself.”
This phenomenon is known as gravitational lensing, where a sufficiently large mass can warp the fabric of spacetime around it. That bends the path of light from distant objects, like stars, quasars and galaxies, so that they appear in different parts of the sky. Sometimes it even splits the light so that it appears in two spots at once, or causes events like supernovae to replay at different times.
The researchers say that next-generation X-ray telescopes should be able to capture X-rays from black holes in higher resolution, which should help unravel more mysteries around them.
The research was published in the journal Nature.
Source: Stanford University
