Supernova is a huge explosion of a star. First supernova observed by man was observed in 185 CE. It was a Chinese astronomer who observed this massive explosion. The location of this supernova is near the direction of Alpha Centauri, between the constellations Circinus and Centaurus. Chinese mentioned this supernova in a Book of Later Han. It is believed that this is the first observed supernova in history.
This supernova was remained observable for at least eight months in the night sky. Since that time, many supernovae have been observed within the Milky Way Galaxy. With improvements in telescopes the observance of supernovae is extended to other galaxies. In 1987 another supernova was observed and for a long time it was considered as a more powerful recent explosion, but another supernova was observed a few days ago in Messier 82 (M82) Galaxy. It is about 12 million light years away from us that means it was exploded about 12 million years ago. It also means that just under 12 million years ago, a star in the M82 galaxy went boom. We're just seeing the effects of that nowhere on Earth. This supernova is getting brighter and can be picked up easily with amateur telescopes. A supernova initiates with the star collapsing when it can no longer support itself against gravity's inner force. After this massive collapse, it explodes its outer covers into space. The core of the star is left behind in of a neutron star or black hole.
A supernova occurs when the stars burn nearly all of their fuel in the fusion reaction. Stars even more massive than our sun detonate with the huge amount of energy.
To understand supernovae easily astronomers have classified them into two types: Type I and Type II. Type I supernova occurs in binary star systems. In a binary star system one star starts pulling off mass from other mass till it reaches at a certain amount of mass. After that an explosion causes a supernova. Most of the times these stars are on the stage of White dwarfs. Astronomers use Type Ia supernovae as standard candle to measure cosmic distances. Type Ib and Type Ic undergo core-collapse. Type I supernova lack hydrogen gas.
The main thing that cause division of supernova in the two types is the presence of hydrogen gas. Type II supernova shows hydrogen signatures. A star, at least 8 to 10 times massive than sun’s mass can go Type II supernova explosion. The reason behind it explosion is also the star will run out of hydrogen and after hydrogen, then helium in its core to burn and will explode. But it will have enough mass to burn carbon. After that heavier elements build up in its core forming a layer like an onion. Once the star's core reaches the Chandrasekhar limit (certain mass limit), the star begins to shrink and due this reason these supernovas are also well-known as core-collapse supernovae. With an explosion the star transforms into a neutron star. Sub categories of Type II supernova are based on their spectral emission of light Type II-L and Type II-P's. Stars much more massive than twenty to thirty solar masses might not discharge as a supernova. Instead, they collapse forming black holes.