Eight Ways for Humanity to Know the Existence of Black Holes

Since a black hole is a celestial body with such a strong gravity that even light cannot escape, its existence cannot be directly observed using not only visible light but also electromagnetic waves of all wavelengths such as X-rays and infrared rays. Live Science, a science news site, has put together eight methods that scientists have devised to discover the existence of such black holes.

8 ways we know that black holes really do exist | Live Science


◆ 1: Albert Einstein's 'firm prophecy'
The term 'black hole' began to be used in the 1960s, but in 1916, German astrophysicist Karl Schwarzschild could form a black hole-equivalent object in the universe. Was expected. Schwarzschild predicted that 'if the general theory of relativity is correct, there will be a black hole,' based on the general theory of relativity published by Einstein from 1915 to 1916.

Then, in 1965, British mathematical physicists Roger Penrose and Stephen Hawking discovered that 'black holes form singularities with infinite density and gravity,' which led to Penrose. He received the 2020 Nobel Physics Award. The reason for the award at this time was 'the discovery that the formation of a black hole is a' firm prophecy 'of the general theory of relativity.'

◆ 2: Gamma-ray burst
Black holes cannot be observed directly, but their existence can be inferred by observing the effects of black holes on the universe. One of them

is the gamma-ray burst, which is known as the 'highest luminosity physical phenomenon' in the field of astronomy.

In the 1930s, Indian astrophysicist Subrahmanyan Chandrasekhar, who was investigating what happened to a star that ran out of fuel, said, 'A star with a certain mass collapses due to its own gravity and collapses into a black hole.' Advocated. At this time, the core of the burned-out star collapses at a tremendous speed of only a few seconds, and the enormous energy generated by this is released into the universe as a gamma-ray burst. The energy of this gamma-ray burst is said to correspond to the total energy released from the birth of a normal star to its burning, and it is possible to know the existence of a black hole by capturing its brilliance.

by NASA Goddard Space Flight Center

◆ 3: Gravitational waves
Not only do black holes exist alone, but multiple black holes can orbit each other. Einstein's general theory of relativity predicted that in this black hole binary , a very strong gravitational interaction could generate gravitational waves that spread ripples in space. And in 2016, the American laser interferometer gravitational wave observatory 'LIGO' succeeded in observing the gravitational wave when the two black holes merged, proving the gravitational wave predicted by Einstein.

Finally succeeded in observing gravity waves, and there is a possibility that space research will be greatly expanded by complementing space observation with light --GIGAZINE

◆ 4: Stars that move strangely
Gamma-ray bursts and collisions between black holes that occur when a star reaches the end of its life are temporary events and cannot be observed at all times. However, even if the astronomical phenomenon generated directly from the black hole cannot be observed, its existence can be indirectly identified by observing the movement of other celestial bodies affected by the gravity of the black hole.

Astronomers at the European Southern Observatory, who were observing a binary star called HR 6819 in 2020, noticed that the binary star with two observable stars was behaving strangely. And astronomers said, 'This binary is actually a black hole.' It must be a three-star star, including. ' The black hole of HR 6819 is the closest known black hole to the earth, and the light emitted by the entire binary star can be seen with the naked eye.

A black hole closest to the solar system is found just 1000 light-years from Earth-GIGAZINE

by L. Calçada / ESO

◆ 5: X-ray
In HR 6819 mentioned above, it is thought that the black hole and the two stars have almost no contact, but if the distance between the black hole and the other celestial body is close enough, the material that makes up the star will be stripped off by the black hole. I will continue.

At this time, the substances that made up the star are not swallowed by the black hole in a straight line, but rotate at high speed around the black hole to form an accretion disk. The accretion disk emits very strong X-rays, and the location of the black hole can be identified by observing the X-rays. Cygnus X-1, which is said to be the first black hole discovered by humankind, was discovered in this way.

◆ 6: Supermassive black hole
Black holes are created by the collapse of stars that cause gamma-ray bursts, as well as

supermassive black holes located in the center of the galaxy. It is said that there is a supermassive black hole in the center of most galaxies, and all kinds of electromagnetic waves such as radio waves, infrared rays, ultraviolet rays, X-rays, and gamma rays are prosperous from the galactic nuclei of special galaxies called active galactic nuclei. Has been released to.

In the center of the Milky Way the Earth is located not seat A in regions that, we found that there is a supermassive black hole with 4 million times the mass of the sun.

◆ 7: Spaghetti
Another phenomenon that indicates the existence of black holes is spaghettification . Spaghettiization means that the celestial body near the black hole is crushed by too much gravity and stretched like spaghetti. In 2020, the moment when a black hole actually makes a star spaghetti and swallows it is observed.

You can capture the moment when a black hole 'spaghettis' a star and swallows it --GIGAZINE

◆ 8: Observe the shadow of a black hole
The ultimate way to know the existence of a black hole is to look at the outline of the black hole. The black hole itself does not emit anything, so it cannot be observed, but by observing the accretion disk surrounding the black hole with extremely high accuracy, you can see the shadow that can be formed on the accretion disk due to the influence of the black hole, that is, the black hole shadow. can do.

In 2019, a project called 'Event Horizon Telescope ' that observes the same place with radio telescopes all over the earth and captures a black hole as if it were one huge telescope, will be a super- large otomeza galaxy group M87. The accretion disk of a mass black hole and the silhouette of a black hole were imaged for the first time.

'Event Horizon Telescope' aiming to capture black hole shadows will hold a press conference --GIGAZINE

by EHT Collaboration

in Science, Posted by log1l_ks