What are Black Holes?

According to wikipedia, a black hole is a region of spacetime exhibiting such strong gravitational effects that nothing, not even particles and electromagnetic radiation such as light, can escape from inside it. The gravity is so strong because matter has been squeezed into a tiny space. The boundary of the region from which no escape is possible is called the *event horizon*. The event horizon is referred to as such because if an event occurs within the boundary, information from that event cannot reach an outside observer, making it impossible to determine if such an event occurred. Although the event horizon has an enormous effect on the fate and circumstances of an object crossing it, no locally detectable features appear to be observed. In many ways a black hole acts like an ideal black body, as it reflects no light.

https://www.nasa.gov/sites/default/files/styles/side_image/public/cygx1_ill.jpg?itok=9BTOTPaU
An artist's drawing a black hole named Cygnus X-1. It formed when a large star caved in. This black hole pulls matter from blue star beside it.
Credits: NASA/CXC/M.Weiss

Albert Einstein first predicted black holes in 1915 with his general theory of relativity and the first strong candidate for a black hole, Cygnus X-1, was discovered in 1972 by Charles Thomas Bolton, Louise Webster and Paul Murdin.

> The American astronomer John Wheeler has the credits for coining the term *black hole* though it was a student who reportedly suggested the phrase at one of his lectures in 1967. A black hole can not be seen because strong gravity pulls all of the light into the middle of the black hole. However, space telescopes with special tools can help find black holes. The special tools can see how stars that are very close to black holes act differently than other stars.

How Black Holes are Formed

Scientists have actually, over the years, discovered a few ways which a black hole can form. They think the smallest blacks holes formed when the universe began, maybe as a result of the *big bang* but the most commonly discussed way black holes form is the "Gravitational Collapse". Gravitational collapse is when an object falls in upon itself. It occurs when an object's internal pressure is insufficient to resist the object's own gravity. When a star has too little fuel left to maintain its temperature through stellar nucleosynthesis, it experiences a gravitational collapse and a black hole is formed. The black hole formed when a star falls in upon itself is called a _**Stellar Black Hole**_. > Once a black hole has formed, it can continue to grow by absorbing gas and interstellar dust from its surroundings, allowing it to grow to an enormous size. This is how _**Supermassive Black Holes**_, which are the largest black holes are formed. These black holes have masses that are more than 1 million suns together.

https://www.nasa.gov/sites/default/files/blackhole_2.jpg
An artist's drawing shows the current view of the Milky Way galaxy. Scientific evidence shows that in the middle of the Milky Way is a supermassive black hole.
Credits: NASA/JPL-Caltech

Scientists have found proof that every large galaxy contains a supermassive black hole at its center. The supermassive black hole at the center of the Milky Way galaxy is called Sagittarius A. It has a mass equal to about 4 million suns and would fit inside a very large ball that could hold a few million Earths.

Scientist also discovered that black holes can actually merge with other objects such as stars or even other black holes. It was on this basis __*Intermediate-Mass Black Holes*__ were propounded.

Could Earth be destroyed by Black Holes Someday?

This is a question many have asked and has been a topic for argument even with those without much scientific knowledge. Some fear that a black hole might appear close to planet earth some day and earth might just fall into it or absorbed by the black hole, as in the case of supermassive black holes. The truth is earth will not fall into a black hole because no black hole is close enough to the solar system for Earth to do that. Even if a black hole the same mass as the sun were to take the place of the sun, Earth still would not fall in. The black hole would have the same gravity as the sun. Earth and the other planets would orbit the black hole as they orbit the sun now. The sun will never turn into a black hole because is not big enough a star to make a black hole.

Some Interesting Facts about Black Holes

* Black Holes of stellar mass possess temperature in order of billionths of a kelvin, making it essentially impossible to observe. * If you fell into a black hole, theory has long suggested that gravity would stretch you out like spaghetti, though your death would come before you reached singularity. But a 2012 study in Nature suggests that quantum effects would cause the event horizon to act much like a wall of fire, instantly burning anyone to death. * Astronomers estimate there are anywhere from 10 million to a billion stellar black holes, with masses roughly three times that of the sun, in the Milky Way. __*References*__ Wikipedia - [Black Hole](https://en.wikipedia.org/wiki/Black_hole) Nasa - [What is a Black Hole](https://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-is-a-black-hole-k4.html) Space.com - [Black Holes: Facts, Theory & Definition](https://www.space.com/15421-black-holes-facts-formation-discovery-sdcmp.html)