A black hole is a region of spacetime where gravity is so strong that no particle, even light cannot escape from it. Einstein’s general theory of relativity predicts that a sufficient compact mass can create a black hole anywhere in spacetime. The point from which nothing can escape is called as event horizon. This gigantic space monster is formed from a dying star. The gravitational pull is so strong because everything is compressed into tiny space.
Formation of Black Holes
Scientists believe that the smallest black hole was formed when the universe was created. Stellar or huge black holes are formed when the core of a huge star falls upon itself or collapses. When this happens, it creates a supernova. Supernova is an exploding star which blasts its outer part into the space. When a star has exhausted the thermal nuclear fuel in its core, it becomes highly unstable and gravitationally collapses upon itself.
The crushing weight of matter falling upon the star from all sides compresses the star to a point of no volume and infinite density. This point is called as the singularity. Singularity is the center of the black hole which is hidden by its surface which is the event horizon. The event horizon is the farthest place a particle can go while travelling towards the black hole. After that, there is the point of no return. This is because the escape velocity, the velocity needed to escape from the gravitational pull of a cosmic object, of a black hole is more than the speed of light.
Discovery of Black Holes
The first black hole ever discovered was Cygnus X-1, located within the Milky Way in the constellation of Cygnus. Astronomers saw the first signs of the black hole in 1964 via the gas it sucked away from a closely orbiting blue supergiant star. As this gas spiraled into the black hole, it became so hot it emitted high-energy X-rays and gamma-rays that satellites could detect. This black hole is about 7,240 light years away from Earth
Scientists detected that there is a supermassive black hole in the center of our galaxy, Milky Way. The black hole, Sagittarius A* is a massive black hole whose mass is equivalent to 4 million suns. In 2017 it was detected that every galaxy consists a super massive black hole in its center. As black holes are invisible, it is detected using special telescopes to study the things happening around the black hole. The Event Horizon telescope is used designed specially to detect black holes around the universe.
First Images of a Black Hole
The first direct visual evidence of a black hole has been revealed on 10 April 2019 by astronomers working on the Event Horizon Telescope. The image is of the supermassive black hole that lies at the center of the huge Messier 87 galaxy, in the Virgo galaxy cluster. Located 55 million light-years from Earth, the black hole has been determined to have a mass 6.5 billion times that of the Sun.
Though black holes are not visible, scientists and researchers managed to capture the boundary – the event horizon of the black hole. The size of the image of the black hole is almost equal to the size of the selfies taken by 10,000 people in their life time. This is considered as a huge achievement as this is the first time an image as clear as this has been captured.