In a discovery aligning closely with Albert Einstein’s predictions, scientists have now observed what can best be described as the “waterfall” of space—a region where matter irrevocably plunges into the abyss of a black hole. This multi-university study was published in the Monthly Notices of the Royal Astronomical Society and provides an interesting glimpse into one of the most mysterious aspects of black hole physics—the plunging region.

Einstein’s general relativity theory states particles cannot safely follow circular orbits when they are close enough to a black hole. Rather, they “plunge” toward the black hole at nearly the speed of light, but very quickly.

For the first time, the study looked at this area in great detail using X-ray data to comprehend the force that black holes produce.

“Einstein’s theory predicted that this final plunge would exist, but this is the first time we have been able to demonstrate it happening,” said Oxford University’s Andrew Mummery who led the study. “Think of it like a river turning into a waterfall – hitherto, we have been looking at the river. This is our first sight of the waterfall.”

Black hole whirlpool

Using data from NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) and the Neutron Star Interior Composition Explorer (NICER) aboard the International Space Station, the team scrutinized the fate of hot, ionized gas as it took its final plunge. This not only verified Einstein’s prediction about the plunging region but also showed it as a site of intense gravitational influence, possibly the strongest in our Milky Way galaxy.

The focus centered on MAXI J1820+070, a black hole system located about 10,000 light-years from Earth. During a ‘soft-state’ outburst, MAXI J1820+070 showed significant emissions from the innermost stable circular orbit (ISCO). This finding indicates that emissions from the plunging region can greatly affect the X-ray spectra observed, influencing the estimated physical characteristics of black holes, like their mass and spin.

The discovery of emissions from the plunging region reshapes our understanding of black hole accretion disks. Traditionally, models assumed that no significant emissions occurred past the ISCO, but the study’s findings highlight a strong detection of intra-ISCO emissions, confirming the area’s active role in black hole dynamics. This observation aligns with the principles of general relativity and initiates a new phase of exploring the surroundings close to black holes.

This discovery opens the door for further research into the environments of farther-off black holes and may improve techniques for more precisely measuring their characteristics. With plans underway for projects like the Africa Millimeter Telescope, which aims to capture direct images of black holes, the potential for further groundbreaking discoveries looks promising.

“This is the first look at how plasma, peeled from the outer edge of a star, undergoes its final fall into the center of a black hole, a process happening in a system around ten thousand light years away,” Mummery said. “What is really exciting is that there are many black holes in the galaxy, and we now have a powerful new technique for using them to study the strongest known gravitational fields.”