Science for Thought

Hypernova

Hypernova

This is also called a superluminous supernova, and it's the brightest thing in the universe. These supernovae light up the entire universe and emit a gamma ray burst that is extremely dangerous. They are capable of wiping life away on nearby planets.

A giant star like Eta Carina (I've already talked about this) could emit a super powerful gamma ray burst our way.
What exactly happens to a star when it goes supernova and how does it end up?

There are two ways that a star could supernova: Type I and Type II. There are sub categories to these two, but we will deal with a Type II supernova.

Type II supernovae involve the sudden collapse of a giant star's core. In order for a star to supernova like this it must have a mass at least 8 times the mass of our sun. What happens is that when the star fuses all of its hydrogen and helium, it heats up because of the gravitational pressure of its outer layers. This causes nuclear fusion to take place to make the higher elements as follows: helium fuses to make carbon and oxygen; carbon fuses to make sodium, neon, magnesium and aluminum; neon fuses to make oxygen and magnesium; oxygen fuses to make silicon, sulfur, argon, and calcium; silicon fuses to make nickel, which decays into iron.

The first stage of hydrogen fusing to make helium occurs at a temperature of 7 times 10 to the 7th power Kelvin. The last stage of fusion is completed at a temperature of 2.5 times 10 to 9th power Kelvin. The density of the core goes from 10 grams/centimeter cubed to 10 to the 8th power g/cm3. The hydrogen fusion reaction takes 10 to the 7th power years. The final step only takes 5 days.

What happens is that the iron can no longer fuse even at that high of a temperature. When the mass of the core consisting of iron exceeds the Chandrasekhar limit of 1.4 times the mass of our sun, it becomes extremely unstable. This causes the core to collapse from a hundred thousand miles in diameter to a few miles at a third of the speed of light, literally in a microsecond. The result is the release of a tremendous amount of energy that causes the outer layers of the star to be blasted off in a horrendous explosion.

This explosion creates temperatures in excess of 10 to the 9th power Kelvin and this creates most of the higher elements like gold, and uranium, and since it only lasts for seconds the amount of these higher elements is scarce.
One of the odd things that occurs when the core collapses is that it become so dense that only neutrinos can escape. Neutrinos are created when electrons and protons combine by electron capture. The fact is that this neutrino burst precedes the actual supernova explosion and their detection is one way that astronomers know that there is a pending supernova.

So what's left after a supernova?

That depends upon the size of the star. Most supernovae result in a white dwarf, but if the star is 20 times the mass of the sun, the core becomes a neutron star. If the star is 40 to 50 times the mass of the sun, the core collapses directly into a black hole.

A hypernova is at least 10 times brighter than a normal supernova. It's this extreme type of superluminous supernova that produces a black hole.

God help us if one of these occurs near us.

Thanks for reading.