Black Holes

 Black holes have fascinated scientists from the early 18th century. The term black hole was coined in 1969 by American scientist John Wheeler. A black hole is a dense object from which even light cannot escape. A star after supernova explosion turns into a black hole. But there is a condition. Only star which has mass more than one and a half times the mass of the sun will turn into a black hole otherwise it will become a white dwarf or a neutron star. This mass is known as the Chandrasekhar limit, after the name of its discoverer Subrahmanyan Chandrasekhar. Black holes are not visible because the light could not escape the strong gravitational field and would not reach us. But still its presence would be felt because of the gravitational attraction on nearby objects.

   source: Wallpapers Vista

There are two parts of a black hole the event horizon and the singularity. The boundary of a black hole is called the event horizon. The central, most dense part is called singularity. Cygnus X-1 was the first identified black hole. The nearest known black hole is about 1000 light years away. Though most on it are theoretical but implementation of equations of General Relativity was first done by Karl Schwarzschild in 1916. The ‘No hair theorem’ explains that the information about the body must be lost only its mass and rate of rotation can be calculated. Stephen hawking showed that large black holes emit slow radiation and slow ones emit a large radiation because of which they glow. This thermal radiation because of quantum effects is known as Hawking radiation.

source: wallup.net

The first picture of a black hole was taken in 2019 using 8 telescopes around the world known as Event horizon telescope with the effort of more than 200 scientists. This black hole was spotted at the centre of M87(Messier 87) about 55 million light years away. The algorithm that created the first image was developed by Katie Bouman. The mysteries of black hole have not been fully solved. But scientists around the world are working continuously in revealing it and consequently revealing the beginning of the universe.

source: cutewallpaper.org