Scientists have confirmed for the first time that the fabric of space-time “sinks” at the edge of a black hole. The observation of this subduction zone around black holes was made by astrophysicists at Oxford University’s Physics department, and it helped confirm a key prediction of Albert Einstein’s 1915 theory of gravity: general relativity.

The Oxford team made the discovery by focusing on regions surrounding stellar-mass black holes in binary systems with companion stars relatively close to Earth. The researchers used X-ray data collected from a number of space telescopes, including NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) and the Neutron Star Interior Composition Explorer (NICER) on the International Space Station.

These data allowed them to determine the fate of the hot ionized gas and plasma ejected from the companion star, eventually sinking to the very edge of the corresponding black hole. The resulting data showed that these so-called subduction zones around the black hole are the locations of some of the strongest points of gravitational influence ever observed in our Milky Way galaxy.

“This is the first look at how plasma stripped from the outer edge of a star undergoes its final fall into the center of the black hole, a process that takes place in a system about 10,000 light-years away,” said the head of the study. Oxford University physics team. – says the testimony of scientist Andrew Mummery. “Einstein’s theory predicted that this final collapse would occur, but this is the first time we have been able to show that it has occurred.

“Think of it like a river turning into a waterfall; So far we have looked at the river. “This is our first time seeing the waterfall.”

Where does a falling black hole come from?

Einstein’s general theory of relativity proposes that massive objects cause deformation of the fabric of space and time and coalesce into a single four-dimensional entity called “spacetime.” Gravity occurs as a result of curvature.

Although general relativity works in 4 dimensions, it can be vaguely illustrated by a rough two-dimensional analogy. Imagine that balls of increasing mass are placed on a stretched rubber sheet. A golf ball causes a small, almost imperceptible dent; a cricket ball will result in a larger dent; and the bowling ball is a huge dent. This is similar to how moons, planets, and stars “cut through” 4D spacetime. As the mass of the object increases, the curvature caused by them also increases and therefore the gravitational effects increase. A black hole is just like a cannonball on a rubber sheet.

By squeezing masses equivalent to tens or even hundreds of suns into Earth-like expanses, the curvature of spacetime and the gravitational influence of stellar-mass black holes can become quite extreme. Supermassive black holes are a completely different story. Them oversized It is so massive that it dwarfs even the masses of stars, with a mass equivalent to millions or even billions of suns.

Turning to general relativity, Einstein suggested that this warping of space-time leads to other interesting physics. For example, he said, there must be a point outside the black hole where particles cannot move in a circular or fixed orbit. Instead, matter entering this region will sink towards the black hole at close to the speed of light.

Astrophysicists’ goal for some time has been to understand the physics of the matter in the subduction zone of this hypothetical black hole. To solve this problem, the Oxford team investigated what happens when black holes are present in a binary system with a “normal” star.

If they are close enough or the star is slightly swollen, the black hole’s gravitational pull can push star material away. Because this plasma has angular momentum, it cannot fall directly onto the black hole, but instead forms a flattened cloud called an accretion disk that orbits around the black hole.

From this accretion disk, matter gradually enters the black hole. According to black hole power models, there should be a point called an internal stable circular orbit (ISCO), which is the last point at which matter can rotate stably in the accretion disk. Any matter beyond this is in the “sink zone” and begins its inexorable descent towards the mouth of the black hole. The debate over whether this subduction zone could be detected was resolved when the Oxford team, outside ISCO, discovered emissions from accretion disks around the Milky Way’s binary black hole, called MAXI J1820+070.

Located about 10,000 light-years from Earth and with a mass of about eight suns, the black hole component MAXI J1820+070 ejects material from its companion star by emitting twin jets at about 80% of the speed of light; It also produces powerful X-rays.

The team found that the X-ray spectrum of MAXI J1820+070 is in a “soft” flare, representing emission from the accretion disk (the full accretion disk, including the dip) surrounding the rotating Kerr black hole. area.

The researchers say this scenario represents the first reliable detection of radiation from a region dipping into the inner edge of a black hole’s accretion disk; they call such signals “intra-ISCO emissions.” These emissions at ISCO confirm the accuracy of general relativity in identifying regions immediately around black holes.

To continue this research, a separate team from Oxford’s Department of Physics is collaborating with a European initiative to build the African Millimeter Telescope. This telescope should improve scientists’ ability to take direct images of black holes and allow them to investigate the subduction zones of more distant black holes.

“What’s really exciting is that there are so many black holes in the galaxy, and we now have a powerful new technique that can use them to study the strongest known gravitational fields,” Mummery concluded.