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The above image is of the supernova remnant, "The Crab Nebula".
It was first seen by the Chinese in 1054. It shone so brightly that it was visible in the daytime.
The nebula itself was discovered in 1731 by John Bevis and then independently in 1758 by Charles Messier. Its around 6000 light-years away.

Please read topic pages "nebulae" and, "planetary nebulae" before venturing further.

There are two types of Supernova, "Type I" and, "Type II".
A "Type I" supernova is a massive thermonuclear bomb, fusing carbon and oxygen at high temperatures to produce most of the iron visible in the Universe.
White dwarf stars have the mass of the Sun in a volume the size of Earth. If their mass exceeds 1.4 solar masses (the "Chandrasekhar limit"), they become unstable. The gravity of a white dwarf in a binary system will pull mass from its companion. It exceeds the Chandrasekhar limit, becomes unstable and rapidly becomes hotter.
When the 6,000km diameter iron core reaches the limits of stability, it cannot support its own gravity and collapses in about a second to form a 30km diameter neutron star.
The collapse of the core causes a shockwave to rip through the star at around 40,000km/s. The star's outer layers are heated and ejected in a supernova.
And a "Type II" supernova:
During the red giant stage, a star at least eight times as massive as our Sun, which has already burned off its supply of hydrogen and helium will continue to transmute carbon into oxygen, neon, sodium, silicon etc. When this process reaches as far as iron then gravity wins and the core implodes down to the size of a neutron star. This releases so much energy that it blows off the outer material in a colossal explosion.
The debris thrown back into space contains all the elements in the periodic table that have been produced up to this point.
Although iron is only the twenty-sixth element in the periodic table, the heat from the supernova explosion can release small traces of uranium and that is number ninety-two in the periodic table!
Eventually all these elements will find themselves back in a nebula where starbirth occurs.

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