Scientists have confirmed, for the first time, that the very structure of space-time takes a “final plunge” at the edge of a black hole.
The observation of this plunging region around black holes was carried out by astrophysicists from the University of Oxford and helps validate 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 binaries with companion stars located relatively close to Earth. The researchers used X-ray data collected from a range of space telescopes, including NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) and the Neutron Star Interior Composition Explorer (NICER) mounted on the International Space Station.
This data allowed them to determine the fate of hot ionized gas and plasma, extracted from a companion star, plunging one last time to the very edge of its associated black hole. The results demonstrated that these so-called dipping regions around a black hole are the location of some of the strongest points of gravitational influence ever observed in our galaxy, the Milky Way.
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“This is the first glimpse of how plasma, peeled off from the outer edge of a star, undergoes its final fall into the center of a black hole, a process taking place in a system about 10,000 years away – light,” said the head of the physics team at the University of Oxford. said scientist Andrew Mummery in a statement. “Einstein’s theory predicted that this final fall would exist, but this is the first time we have been able to demonstrate that it happens.
“Think of it like a river turning into a waterfall: until now we’ve looked at the river. This is the first time we’ve seen the waterfall.”
Where does the black hole dive come from?
Einstein’s theory of general relativity suggests that objects with mass cause the very fabric of space and time to warp, united into a single four-dimensional entity called “space-time.” Gravity results from the resulting curvature.
Although general relativity works in 4D, it can be vaguely illustrated by a crude analogy in 2D. Imagine placing spheres of increasing masses on a stretched sheet of rubber. A golf ball would cause a small, almost imperceptible dent; a cricket ball would result in a larger dent; and a bowling ball a huge bump. This is analogous to moons, planets and stars “damaging” 4D spacetime. As the mass of an object increases, the curvature it causes also increases and, therefore, its gravitational influence increases. A black hole would be like a cannonball on this analogous rubber sheet.
With masses equivalent to tens or even hundreds of suns compressed to a width around that of Earth, the curvature of space-time and the gravitational influence of stellar-mass black holes can become quite extreme. Supermassive black holes, on the other hand, are a completely different story. They are extremely massive, with masses equivalent to millions or even billions of suns, dwarfing even their stellar-mass counterparts.
Returning to general relativity, Einstein suggested that this curvature of space-time leads to other interesting physics. For example, he says, there must be a point just outside the limits of the black hole where the particles would be unable to follow a circular or stable orbit. Instead, matter entering this region would plunge toward the black hole at speeds close to light.
Understanding the physics of matter in this hypothetical plunging region of a black hole has been a goal of astrophysicists for some time. To solve this problem, the Oxford team studied what happens when black holes exist in a binary system with an “ordinary” star.
If the two are close enough, or if that star is slightly inflated, the gravitational influence of the black hole can tear away stellar matter. Since this plasma has angular momentum, it cannot fall directly toward the black hole. It therefore forms a flattened rotating cloud around the black hole called the accretion disk.
From this accretion disk, matter is gradually transported towards the black hole. According to black hole power models, there should be a point called the innermost stable circular orbit (ISCO) – the last point where matter can remain in stable rotation in an accretion disk. Any matter beyond is in the “dive region” and begins its inevitable descent toward the black hole’s maw. The debate over whether this diving region could ever be detected was settled when the Oxford team discovered emissions just beyond the ISCO from accretion disks around a binary black hole of the Milky Way called MAXI J1820+070.
Located about 10,000 light years from Earth with a mass of about eight suns, the black hole component of MAXI J1820+070 extracts matter from its stellar companion while throwing out twin jets at about 80 percent of the speed of the light ; it also produces strong X-ray emissions.
The team discovered that the X-ray spectrum of MAXI J1820+070 in a “soft-state” explosion, which represents the emission from an accretion disk surrounding a rotating black hole, or “Kerr” , — a complete accretion disk, including the plunging black hole. region.
The researchers say this scenario represents the first robust detection of emission from a dipping region located at the inner edge of a black hole accretion disk; they call these signals “intra-ISCO emissions”. These intra-ISCO emissions confirm the accuracy of general relativity in describing the regions immediately around black holes.
To follow up on this research, a separate team from Oxford’s physics department is collaborating with a European initiative to build the African Millimeter Telescope. This telescope is expected to improve scientists’ ability to capture direct images of black holes and make it possible to probe the diving regions of more distant black holes.
“What’s really exciting is that there are many black holes in the galaxy, and we now have a powerful new technique to use them to study the strongest known gravitational fields,” concluded Mummery.
The team’s research is published in the journal Monthly Notices of the Royal Astronomical Society.