What is a black hole

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You may have heard the term black holes,but what it is,what it does,and how it is formed here you will find a deep detail of it even if you are totally newbie to these kind of terms.so we will start with a little definition

A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing—including particles and electromagnetic radiation such as light—can escape from inside it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of the region from which no escape is possible is called the event horizon. Although crossing the event horizon has enormous effect on the fate of the object crossing it, it appears to have no locally detectable features. In many ways a black hole acts like an ideal black body, as it reflects no light. Moreover, 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 on the order of billionths of a kelvin for black holes of stellar mass, making it essentially impossible to observe.

When it was first discovered

Albert Einstein first predicted black holes in 1916 with his general theory of relativity. The term “black hole” was coined in 1967 by American astronomer John Wheeler, and the first one was discovered in 1971.

How it is formed

A common type of black hole is produced by certain dying stars. A star with a mass greater than about 20 times the mass of our Sun may produce a black hole at the end of its life.

In the normal life of a star there is a constant tug of war between gravity pulling in and pressure pushing out. Nuclear reactions in the core of the star produce enough energy and pressure to push outward. For most of a star’s life, gravity and pressure balance each other exactly, and so the star is stable. However, when a star runs out of nuclear fuel, gravity gets the upper hand and the material in the core is compressed even further. The more massive the core of the star, the greater the force of gravity that compresses the material, collapsing it under its own weight.

For small stars, when the nuclear fuel is exhausted and there are no more nuclear reactions to fight gravity, the repulsive forces among electrons within the star eventually create enough pressure to halt further gravitational collapse. The star then cools and dies peacefully. This type of star is called a “white dwarf.”

When a very massive star exhausts its nuclear fuel it explodes as a supernova. The outer parts of the star are expelled violently into space, while the core completely collapses under its own weight.

If the core remaining after the supernova is very massive (more than 2.5 times the mass of the Sun), no known repulsive force inside a star can push back hard enough to prevent gravity from completely collapsing the core into a black hole.

From the perspective of the collapsing star, the core compacts into a mathematical point with virtually zero volume, where it is said to have infinite density. This is called a singularity.

Where this happens, it would require a velocity greater than the speed of light to escape the object’s gravity. Since no object can reach a speed faster than light, no matter or radiation can escape. Anything, including light, that passes within the boundary of the black hole — called the “event horizon” — is trapped forever.

Types of blackholes

There are three types: stellar black holes, supermassive black holes and intermediate black holes.

When a star burns through the last of its fuel, it may find itself collapsing. For smaller stars, up to about three times the sun’s mass, the new core will be a neutron star or a white dwarf. But when a larger star collapses, it continues to fall in on itself to create a stellar black hole.

Black holes formed by the collapse of individual stars are (relatively) small, but incredibly dense. Such an object packs three times or more the mass of the sun into a city-size range. This leads to a crazy amount of gravitational force pulling on objects around it. Black holes consume the dust and gas from the galaxy around them, growing in size.

According the Harvard-Smithsonian Center for Astrophysics, “the Milky Way contains a few hundred million” stellar black holes.stellar-black-hole.jpg

Small black holes populate the universe, but their cousins, supermassive black holes, dominate. Supermassive black holes are millions or even billions of times as massive as the sun, but have a radius similar to that of Earth’s closest star. Such black holes are thought to lie at the center of pretty much every galaxy, including the Milky Way.

Scientists aren’t certain how such large black holes spawn. Once they’ve formed, they can easily gather mass from the dust and gas around them, material that is plentiful in the center of galaxies, allowing them to grow to enormous sizes.black_hole_spin.jpg

Scientists once thought black holes came in only small and large sizes, but recent research has revealed the possibility for the existence of midsize, or intermediate, black holes (IMBHs). Such bodies could form when stars in a cluster collide in a chain reaction. Several of these forming in the same region could eventually fall together in the center of a galaxy and create a supermassive black hole.

In 2014, astronomers found what appeared to be an intermediate-mass black hole in the arm of a spiral galaxy.

“Astronomers have been looking very hard for these medium-sized black holes,” co-author Tim Roberts, of the University of Durham in the United Kingdom, said in a statement.

“There have been hints that they exist, but IMBH’s have been acting like a long-lost relative that isn’t interested in being found.”

Some bizarre facts about blackholes

  • The massive gravitational influence of a black hole distorts space and time in the near neighborhood. The closer you get to a black hole, the slower time runs. Material that gets too close to a black hole gets sucked in and can never escape.
  • Material spirals in to a black hole through an accretion disk — a disk of gas, dust, stars and planets that fall into orbit the black hole.
  • The “point of no return” around a black hole is called the “event horizon”. This is the region where the gravity of the black hole overcomes the momentum of material spinning around it in the accretion disk. Once something cross the event horizon, it is lost to the pull of the black hole.
  • Black holes were first proposed to exist in the 18th century, but remained a mathematical curiosity until the first candidate black hole was found in 1964. It was called Cygnus X-1, an x-ray source in the constellation Cygnus.
  • Black holes do not emit radiation on their own. They are detected by the radiation given off as material is heated in the accretion disk, and also by the black hole’s gravitational effect on other nearby objects (or light passing by).

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