Black Hole

Jai Ganesh · 2025-08-06 21:27:02

Black hole

Gist

A black hole is a region in spacetime where gravity is so strong that nothing, not even light, can escape. This occurs when a massive amount of matter is squeezed into a tiny space, warping the fabric of spacetime. Black holes are not actually holes, but rather extremely dense objects, and they are invisible, though their presence can be inferred from their gravitational effects on nearby matter.

Inside a black hole, there's a point of infinite density called a singularity, surrounded by the event horizon, the boundary beyond which nothing can escape. General relativity predicts the singularity, but its exact nature is unknown, and current physics theories break down there.

Summary

A black hole is a massive, compact astronomical object so dense that its gravity prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. The boundary of no escape is called the event horizon. A black hole has a great effect on the fate and circumstances of an object crossing it, but has no locally detectable features according to general relativity. In many ways, a black hole acts like an ideal black body, as it reflects no light. Quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is of the order of billionths of a kelvin for stellar black holes, making it essentially impossible to observe directly.

Objects whose gravitational fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace. In 1916, Karl Schwarzschild found the first modern solution of general relativity that would characterise a black hole. Due to his influential research, the Schwarzschild metric is named after him. David Finkelstein, in 1958, first published the interpretation of "black hole" as a region of space from which nothing can escape. Black holes were long considered a mathematical curiosity; it was not until the 1960s that theoretical work showed they were a generic prediction of general relativity. The first black hole known was Cygnus X-1, identified by several researchers independently in 1971.

Black holes typically form when massive stars collapse at the end of their life cycle. After a black hole has formed, it can grow by absorbing mass from its surroundings. Supermassive black holes of millions of solar masses may form by absorbing other stars and merging with other black holes, or via direct collapse of gas clouds. There is consensus that supermassive black holes exist in the centres of most galaxies.

The presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as visible light. Matter falling toward a black hole can form an accretion disk of infalling plasma, heated by friction and emitting light. In extreme cases, this creates a quasar, some of the brightest objects in the universe. Stars passing too close to a supermassive black hole can be shredded into streamers that shine very brightly before being "swallowed." If other stars are orbiting a black hole, their orbits can be used to determine the black hole's mass and location. Such observations can be used to exclude possible alternatives such as neutron stars. In this way, astronomers have identified numerous stellar black hole candidates in binary systems and established that the radio source known as Sagittarius A*, at the core of the Milky Way galaxy, contains a supermassive black hole of about 4.3 million solar masses.

Details

A black hole is a cosmic body of extremely intense gravity from which nothing, not even light, can escape. A black hole can be formed by the death of a massive star. When such a star has exhausted the internal thermonuclear fuels in its core at the end of its life, the core becomes unstable and gravitationally collapses inward upon itself, and the star’s outer layers are blown away. The crushing weight of constituent matter falling in from all sides compresses the dying star to a point of zero volume and infinite density called the singularity.

Details of the structure of a black hole are calculated from Albert Einstein’s general theory of relativity. The singularity constitutes the centre of a black hole and is hidden by the object’s “surface,” the event horizon. Inside the event horizon the escape velocity (i.e., the velocity required for matter to escape from the gravitational field of a cosmic object) exceeds the speed of light, so that not even rays of light can escape into space. The radius of the event horizon is called the Schwarzschild radius, after the German astronomer Karl Schwarzschild, who in 1916 predicted the existence of collapsed stellar bodies that emit no radiation. The size of the Schwarzschild radius is proportional to the mass of the collapsing star. For a black hole with a mass 10 times as great as that of the Sun, the radius would be 30 km (18.6 miles).

Only the most massive stars—those of more than three solar masses—become black holes at the end of their lives. Stars with a smaller amount of mass evolve into less compressed bodies, either white dwarfs or neutron stars.

Black holes usually cannot be observed directly on account of both their small size and the fact that they emit no light. They can be “observed,” however, by the effects of their enormous gravitational fields on nearby matter. For example, if a black hole is a member of a binary star system, matter flowing into it from its companion becomes intensely heated and then radiates X-rays copiously before entering the event horizon of the black hole and disappearing forever. One of the component stars of the binary X-ray system Cygnus X-1 is a black hole. Discovered in 1971 in the constellation Cygnus, this binary consists of a blue supergiant and an invisible companion 14.8 times the mass of the Sun that revolve about one another in a period of 5.6 days.

Some black holes apparently have nonstellar origins. Various astronomers have speculated that large volumes of interstellar gas collect and collapse into supermassive black holes at the centres of quasars and galaxies. A mass of gas falling rapidly into a black hole is estimated to give off more than 100 times as much energy as is released by the identical amount of mass through nuclear fusion. Accordingly, the collapse of millions or billions of solar masses of interstellar gas under gravitational force into a large black hole would account for the enormous energy output of quasars and certain galactic systems.

One such supermassive black hole, Sagittarius A*, exists at the centre of the Milky Way Galaxy. Observations of stars orbiting the position of Sagittarius A* demonstrate the presence of a black hole with a mass equivalent to more than 4,000,000 Suns. (For these observations, American astronomer Andrea Ghez and German astronomer Reinhard Genzel were awarded the 2020 Nobel Prize for Physics.) Supermassive black holes have been detected in other galaxies as well. In 2017 the Event Horizon Telescope obtained an image of the supermassive black hole at the centre of the M87 galaxy. That black hole has a mass equal to six and a half billion Suns but is only 38 billion km (24 billion miles) across. It was the first black hole to be imaged directly. The existence of even larger black holes, each with a mass equal to 10 billion Suns, can be inferred from the energetic effects on gas swirling at extremely high velocities around the centre of NGC 3842 and NGC 4889, galaxies near the Milky Way.

The existence of another kind of nonstellar black hole was proposed by the British astrophysicist Stephen Hawking. According to Hawking’s theory, numerous tiny primordial black holes, possibly with a mass equal to or less than that of an asteroid, might have been created during the big bang, a state of extremely high temperatures and density in which the universe originated 13.8 billion years ago. These so-called mini black holes, like the more massive variety, lose mass over time through Hawking radiation and disappear. If certain theories of the universe that require extra dimensions are correct, the Large Hadron Collider could produce significant numbers of mini black holes.

Additional Information

Black holes are some of the strangest and most fascinating objects in the universe. They're extremely dense, with gravitational forces so strong, that nothing, not even lights, can escape once it crosses the boundary known as the event horizon.

The Milky Way could contain over 100 million black holes, though detecting these gluttonous beasts is very difficult. At the heart of the Milky Way lies a supermassive black hole — Sagittarius A*. The colossal structure is about 4 million times the mass of the sun and lies approximately 26,000 light-years away from Earth, according to a statement from NASA.

The first image of a black hole was captured in 2019 by the Event Horizon Telescope (EHT) collaboration. The striking photo of the black hole at the center of the M87 galaxy 55 million light-years from Earth thrilled scientists around the world.

KerimF · Yesterday 21:12:31

I may be wrong, but this is how I expected the existence of what we may call 'black holes'.

As the atomic universe forms the various matters of our universe, I use to see our universe, in turn, forming matter of a much bigger universe.
If an atomic particle escapes from a matter in our universe, the possibility for it, in general, to return to that matter, from where it exited, is close to zero.

Similarly, if a particle (planet, star... even light and the like) escapes from our universe (forming a piece of matter in the higher universe), the possibility for it to return back is close to zero too.

In brief, a 'black hole' is an exit from our universe with no return; as the light in a room crossing one of its windows (one of its black holes).

Last edited by KerimF (Yesterday 21:16:07)

Jai Ganesh · Yesterday 21:20:27

Read the entire post again. If you still believe you are right, you are entitled to your opinion.

KerimF · Today 00:12:56

Jai Ganesh wrote:

Read the entire post again. If you still believe you are right, you are entitled to your opinion.

You are right.
It is clear that I am totally wrong based on what the representatives of the today's science say.

Jai Ganesh · Today 00:40:35

Fine! Knowledge prevails!

Math Is Fun Forum

#1 2025-08-06 21:27:02

Black Hole

#2 Yesterday 21:12:31

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