Corollary to Einstein's theory
In 1916, Karl Schwarzschild predicted black holes as a theoretical
Gamma-ray bursts
In the 1930s, Indian astrophysicist SubramanianChandrasekhar studied what happens to a star when it runs out of fuel. He found that the end result depends on the mass of the star. If this star is really large, say, with a mass of 20 Suns, then its dense core collapses down to a black hole.
Gamma-ray bursts detected by ground-based equipment. (Image credit: NASA / Swift / Cruz deWilde)
All this happens incredibly quickly, inin a matter of seconds, and releases a huge amount of energy in the form of a gamma-ray burst. This flare can emit as much energy into space as an ordinary star emits during its entire life. And telescopes on Earth have detected several such events where black holes are born, despite a distance of billions of light years.
Gravitational waves
Black holes don't always exist in isolation -sometimes they appear in pairs, orbiting each other. When they do this, the gravitational interaction between them creates ripples in spacetime that spread out as gravitational waves. By the way, this is another prediction of Einstein's theory of relativity.
An artist's impression of gravitational waves.Black holes orbiting each other create ripples in spacetime that travel outward in gravitational waves. (Image courtesy of R. Hurt / Caltech-JPL)
Observatories such as LIGO and Virgo give scientiststhe ability to detect these waves. Physicists announced the first discovery related to the merger of two black holes back in 2016. As the detector's sensitivity increases, scientists are detecting other events that have triggered gravitational waves. For example, the collision between a black hole and a neutron star, which took place far beyond the Milky Way, at a distance of 650 million to 1.5 billion light years from Earth.
Invisible satellite
Another proof of the existence of black holes— their gravitational influence on other stars. While observing the usual pair of rotating stars HR 6819 in 2020, astronomers noticed oddities in their movement.
The artist's print shows the orbits of objects in the HR 6819 triple system. (Image courtesy of L. Calzada / ESO)
They can only be explained by the presencethird, completely invisible object. Scientists calculated its mass - it turned out to be four times that of the Sun - and realized that it could only be a black hole. By the way, it is one of the closest to Earth, located only 1000 light-years from it.
X-ray object
The very first object that scientists recognizedthe object Cygnus X-1 (or Cyg X-1) became a black hole. This is an X-ray source in the constellation Cygnus, discovered in 1964. Almost immediately, astronomers assumed that the source of the radiation was a black hole, which is located in a binary system together with a blue supergiant. However, many experts believed that all evidence of its existence was indirect, and Cygnus X-1 could be, for example, a neutron star. British astronomer and popularizer of science Stephen Hawking bet in 1974 that this is not so.
The main obstacle to recognizing Cygnus X-1 as a black hole is the uncertainty of the distance to the object. However, in 2011, astronomers calculated it.
The black hole Cygnus X-1 is pulling material from a massive blue companion star. (Image courtesy of NASA / CXC)
The authors of the new work analyzed the datacollected by the Very Long Baseline Array radio telescopes. According to scientists, the distance to Cygnus X-1 is 6050 light years ±400 light years. Moreover, the mass of the blue supergiant is 19 times the mass of the Sun, and the X-ray source itself is 14.8 times the solar mass.
The new mass value is much greater than the critical valuethe limit that separates a neutron star and a black hole (after “death” a large star can turn into one of these objects). Thus, the new work provides evidence that the very first black hole is indeed one.
Supermassive black holes
Scientists' data indicate that in addition toOrdinary black holes exist and supermassive ones. Each of them has millions or even billions of solar masses, and they hide in the centers of galaxies from the very beginning of the history of the Universe.
At the center of our galaxy lies a supermassive black hole in a region known as Sagittarius A.
(Image credit: ESA - C. Carreau)
According to NASA, central black holes ingalaxies are surrounded by accretion disks that emit intense radiation at all wavelengths of light. Scientists have evidence that one of them - the massive and compact object Sgr A * (Sagittarius A *) - is located in the center of the Milky Way. The closer the stars are to it, the more they rotate - up to 8% of the speed of light. The Milky Way's central black hole is currently estimated to be about 4 million solar masses.
Spaghettification
More evidence for the existence of black holes -this is spaghettification. During this process, the black hole's tremendous gravitational force pulls the object into thin strands. This usually happens with a star that has approached a black hole. In October 2020, astronomers witnessed spaghettification. They saw a flash of light from a star as a black hole ripped it apart. It happened in a galaxy 215 million light years from Earth.
And finally - a direct image
In April 2019, scientists obtained the first ever direct image of the supermassive black hole at the center of the active galaxy Messier 87.
Accretion disc
This photograph was taken by astronomers usingthe Event Horizon telescope. In fact, this is not one instrument, but a large network of telescopes scattered around the world. The photo clearly shows the dark shadow of a 6.5 billion solar black hole against the orange glow of the surrounding accretion disk.
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LIGO (Laser Interferometer Gravitational-Wave Observatory) is a laser-interferometric gravitational-wave observatory.
Virgo is a French-Italian gravitational wave detector located at EGO (European Gravitational Observatory).