A gas falling into a black hole, permanently isolated from the rest of the universe. In the last moments of these gas debris, they emit the last beam of light, one of the brightest radiations in the universe. For humans, the “death fall” of these gases is too far away to be directly observed. But astronomers have devised a new technique that can detect their final traces of radiation and gain insight into the most extreme gravitational environments in the universe.
In the new study, physicists calculated the closest way to avoid falling into a black hole by looking at specific radiation characteristics. This threshold is known as the innermost stable circular orbit ( ISCO). In this way, the more sensitive X-ray telescopes of the future may actually unlock this orbit.
Black holes are undoubtedly the most mysterious objects in the universe, hiding in the dark, devouring all the light that enters. All black holes, regardless of size, share common characteristics, which is the event horizon. Cross this line and you won’t come back. Once anything crosses the horizon of events, even the light itself cannot return to the universe. The gravitational pull of black holes in this region is too strong. Outside the region, however, business as usual.
Black holes have a certain mass, some of which are only a few times the mass of the sun, distributed in smaller galaxies, and billions of times the mass of the sun, making them the true “monsters” of the universe. Orbiting a black hole is like orbiting other large mass objects. Gravity is gravity, and orbit is orbit. Supermassive black holes, because of their powerful gravity, can aaccumulate matter moving to their vicinity, such as gases, stars, etc. The absorbent matter usually has angular momentum, which surrounds the black hole to form a rotating accretion disk or a thicker accretion stream, some of which eventually enters the black hole. Because of the denseness and strong gravity of the black hole, the black hole’s accretion process releases a large amount of gravitational energy, which is converted into the kinetic energy of the absorbent matter, some of which dissipates the gas’s internal energy due to the “friction” between gases or the action of magnetic fields. The black hole accretion process is probably the most efficient physical process in the known universe, with an energy conversion rate of dozens of times that of thermonuclear fusion energy.
As a result, much of the matter in the universe revolves around black holes. Once these “reckless adventurers” are surrounded by the gravitational pull of black holes, they begin their journey toward the end of life. When matter falls into a black hole, it is often squeezed into a disk called a “accretion disk”. The disk rotates non-stop, with the release of heat, friction, magnetic energy, and electrical energy, giving bright light to the material.
In the case of the largest black holes, the accretion disks around them emit so much light that they have a new name: active galactic nuclei ,AGN, which can be more than millions of individual galaxies. In the accretion disk, the blocks of matter rub against each other, suck away their respective rotational energy, and push them continuously toward the black hole’s open event horizon. But without these frictions, matter can orbit black holes forever, just as planets have been orbiting the sun for billions of years.
The closest black hole to Earth
Astronomers at the European Southern Observatory (ESO) have made a remarkable discovery of the black hole that has so far reached Earth. If the conclusion holds, people in the southern hemisphere could even see the star system in which the black hole is located without the use of observation devices.
The mysterious black hole, located 1,000 light-years south of the Constellation of Taurus, is unobservable and has such a strong gravitational force that no object, even light, can escape the gravitational bond of the black hole. Astronomers initially thought it was a binary system or two stars orbiting a central mass object, and when they used MPG/ESO2.2 diameter land-based telescopes for in-depth observations, they named the binary system HR 6819, and to their surprise, they also observed a third object, a black hole.
Although astronomers cannot observe the black hole directly, they can infer its existence based on its gravitational interaction with two companion stars. After several months of observation, they were able to map the orbit of the star and infer that another large, invisible object played an important role in the binary system.
Observations also show that one of the two-star systems orbits the invisible object every 40 days, while the other remains independently in a farther area from the invisible object. They calculated that the invisible object was a star-mass black hole, formed by the collapse of a dying star, about four times the mass of the sun.
In addition to the HR 6819 black hole, the closest black hole to Earth is in the constellation Kirin, 3,000 light-years away, but scientists have analyzed the possibility that there may still be a potential black hole closer, possibly only millions in the Milky Way.
So there may be more black holes hidden near us.
The disappearance of the gas
However, as you get closer to the center of the black hole, you reach a point where all hopes for stability will be dashed by gravity. At this point you are outside the black hole, and have not yet reached the event horizon, but gravity has become so extreme that there is no stable orbit.
The first human black hole photos, published last year, allow us to test general relativity in a highly gravitational environment like the edge of a black hole. The EHT discovery comes from the Messier 87 (M87) black hole. The black hole casts a silhouette on the “background wall” of the radiation that accumulates gas around it. Such a “shadow” is created because the black hole will engulf all the light that emits from behind it and shoots at the observer. At the same time, other light from behind the black hole that just sweeps across the horizon brightens the shadows and forms a bright region. A powerful gravitational lens effect bends light, and even the light emitted by matter directly behind a black hole can be bent around a dark area to contribute a part of the “light”.
Once you reach this area, you can’t stay in a calm orbit, but have only two options: you can push yourself to safety with rockets or other energy, and if you’re a bad gas, you’ll have to fall freeand and fall into endless darkness.
Of course, Einstein’s general theory of relativity also predicted the existence of the innermost stable circular orbit, but despite the success of general relativity in predicting and interpreting cosmic phenomena, and our conviction that black holes are real, scientists have never confirmed the existence of the innermost stable circular orbits and whether they conform to the predictions of general relativity. Now, astronomers have found a way out of the gas that falls into the black hole that could prove the existence of the orbit.
A team of astronomers has described how to use the impending light to study the innermost stable circular orbit. Their method relies on an astronomical technique called reverberation mapping, which uses the characteristic of different regions around black holes emitting light in different ways.
When the gas flows out of the accretion disk and passes through the innermost stable circular orbit (the innermost part of the accretion disk), it becomes very hot and emits a large number of high-energy X-rays. X-rays are sent from black holes in all directions. We can observe these radiations from Earth, but the details of the accretion disk structure disappear in the light of the X-ray (more knowledge of the accretion disk will also help astrophysicists understand the innermost stable circular orbit).
Similarly, these X-rays illuminate areas other than the accretion disk, which are composed mainly of cold gas clumps. Cold gases are stimulated by X-rays and begin to glow, a process known as fluorescence. We can also detect this radiation and distinguish it from the X-rays emitted by the closest region of the black hole.
It takes some time for light to spread from the outer most inner stable circular orbit and the outside of the accretion disk to the cold gas mass, and if we look closely, we can first see the flash of the central area (the innermost stable circular orbit and the innermost part of the accretion disk), and soon the outer side of the innermost stable circular orbit and around the accretion disk will appear bright lying.
The timing and details of these reflected light are dependent on the structure of the accretion disk, which astronomers have previously used to estimate the mass of supermassive black holes at the center of the active galaxy. In the new study, the researchers used sophisticated computer simulations to look at the motion of the gas inside the innermost stable circular orbit, which is how the gas disappears when it eventually falls into the black hole event horizon, and how this in turn affects X-rays emitted from nearby and external gases.
Although current telescopes do not have sufficient sensitivity to measure these gases, the next generation of X-ray telescopes should be able to confirm the existence of the innermost stable circular orbit and verify that it conforms to the general relativity predictions.
Where will black holes lead?
If you could cross a black hole, where would you go? What’s waiting for you? If you could come back unscathed, what interesting story could you tell?
All of these questions can be answered in a simple way: “Who knows?” “In today’s ever-changing science and technology, the mysteries of black holes remain unfathomable. After falling into the event horizon, it was actually over a barrier. Once someone falls, they can no longer send the information back, and they will be torn to pieces by the great gravity. So in theory, anyone who crosses the horizon of an event doesn’t go anywhere.
This may sound like a disappointing and painful answer, but it is also to be expected. Einstein’s general theory of relativity linked space-time to gravitational forces, predicting the existence of black holes, which were later shown to be caused by the death of stars large enough. When a star dies, it leaves behind a small, dense residual core, assuming that the mass of the core is about three times that of the sun, then gravity will cause it to collapse into a point called a “wonder point” (also known as a gravitational wonder or space-time odd ity), a point that is infinitely small, dense, gravitationally infinite, space-time curvature, and is considered to be the center of a black hole.
The resulting black hole has an extremely powerful gravitational pull that even light cannot escape. So if you find yourself in the realm of events, you’re doomed to have nowhere to run. Karl Schwarzschild, a German astronomer, calculated that if the full mass of an object were compressed into a very small “gravitational radius”, all its material and energy, including light, would be trapped by gravity. From the outside, this object is the existence of absolute darkness, that is, a black hole. Event horizons are the spatial and temporal boundary around a black hole, and light and matter can only pass inward through the event horizon. According to Macy’s, tidal forces shrink your body into an atomic chain (also known as “pasta”) and eventually crush at the odd spot. You might want to escape from the other end of the black hole, but that seems to be a complete fantasy. (Any day)
Author: Paul Sutter (astrophysicist)
Compilation: Any day