For the first time, astronomers have observed light coming from behind a black hole, once again confirming Albert Einstein’s theories. Scientists were observing X-rays erupting from a supermassive black hole at the center of the spiral galaxy Zwicky 1, located 800 million light-years away, when they encountered an unexpected discovery.

Along with the anticipated X-ray bursts from the front of the black hole, they also noticed “luminous echoes” that they initially couldn’t explain

What was even stranger was that these out-of-place light flashes were smaller, appeared later, and were a different color compared to the X-ray flares observed from the front of the black hole.

The researchers soon realized that the echoes were actually coming from behind the supermassive black hole. As Einstein’s theory of general relativity predicted, the black hole was warping space-time, allowing the light to curve around it.

“Any light that falls into that black hole doesn’t escape, so we shouldn’t see anything from behind it,” explained Dan Wilkins, a research scientist at the Kavli Institute for Particle Astrophysics and Cosmology at Stanford University, in a statement. “The reason we can see this light is that the black hole is distorting space, bending light, and twisting magnetic fields around it.”

Einstein’s theory of general relativity explains that massive objects distort the fabric of space-time. According to Einstein, gravity isn’t an invisible force but our experience of space-time bending in response to matter and energy.

This distorted space, in turn, dictates how energy and matter move. While light normally travels in a straight line, light passing through a highly curved space-time, like the area around a black hole, will also bend — in this case, from the back of the black hole to the front.

Although astronomers have observed black holes bending light before, a phenomenon known as gravitational lensing, this is the first instance of them detecting light echoes from behind a black hole.

The researchers were not initially aiming to prove Einstein’s theory, which dates back to 1915. Instead, they were using the European Space Agency’s XMM-Newton and NASA’s NuSTAR space telescopes to study the light from the super-hot cloud of particles, called the corona, that forms just outside a black hole’s event horizon.

This cloud of hot particles, or corona, surrounds the black hole and heats up as it gets closer. According to the scientists, the corona’s temperatures can reach millions of degrees, turning the particles into a magnetized plasma as electrons are stripped from atoms. As the black hole spins, the combined magnetic field of the corona arcs high above the black hole before snapping, which leads to the release of X-rays from the corona.

“This magnetic field gets tangled and eventually snaps near the black hole, which heats the surrounding material and creates high-energy electrons that emit X-rays,” Wilkins explained.

Now that they’ve made this groundbreaking observation, the researchers plan to investigate more closely how light bends around black holes and explore how black hole coronas produce such bright X-ray flashes.

The researchers published their findings in the journal Nature.