Death of stars is based on one thing mass. Not the mass they have when born, but the mass they have when they die.
Star Death for mass 1.4 solar masses and less. These stars started big 7.5-10 solar masses. Lives as mainsequence then becomes a red Giant. It will make Carbon and sometimes Oxygen then the core runs out and contracts
It will get a million times denser than water. It has just become a white dwarf.
As the core contracts electrons get squeezed closer together. This state of being so is called Degenerate electrons. White dwarfs with Degenerate electron cores cannot contract any further. A teaspoon of white dwarf would weigh more than a garbage truck.
The more mass a white dwarf has the smaller it gets. The theory is that a white dwarf with a mass of 1.4 solar masses or more will have a radius of zero. The limit of 1.4 solar masses to become a white dwarf is the Chandrasekhar limit.
Chandrasekhar in Indian- American astrophysicist. Figured out the more mass a dying star has the smaller it gets.
Over billions of years it will radiate heat till it cools down to a black lump the size of a planet but the mass of a star. This is a Black dwarf.
It will be made of C and O. As the Black dwarf cools the atoms will solidify into a giant lattice ( rows of atoms) like Diamonds. A Reminder whether it will be a white dwarf or not depends on the amount of mass it has when it is a red giant.
If you find a star cluster with a white dwarf in it this could still be a young group of stars. Large stars up to 7.5 solar masses can lose enough mass and die like our sun.
Large star Deaths With the weight of bigger stars the carbon and oxygen in the core can contract to make larger elements like neon and magnesium. With each element that is made the core contracts more.
The last element it makes is Iron. A massive star does this whole process quickly. In months or even days. The fusion of silicon to iron is the end of fusion under peaceful conditions. Iron is so tightly bound and stable energy is not released it is absorbed.
Larger stars with masses greater that 10 solar masses collapse thru Electron degeneracy. This forces electrons into the nucleus of an atom. Protons and electrons are forced together to make neutrons. They reach a point in the core where neutrons push back, Neutron degeneracy.
The star is made of neutrons. There is a limit. It cannot have a mass greater than 3 solar masses. This is a Neutron star.
It the core is greater than 3 solar masses then neutron degeneracy will not stop it the collapse and it will collapse into a black hole
Neutron degeneracy stops the contraction suddenly this makes a shock wave radiating thru the upper levels of the neutron star. This is the start of the explosion. Total energy in neutrinos is huge. The shockwave combined with the neutrinos makes an explosion in the first second at a level of 10 to the 46 power watts.
This sends amounts of the star spewed out into space. This explosion is a supernova.
This is a type II supernova.
This is the end of a massive star. The material blown into space will be recycled to make new stars and planets.
During the explosion a flood of energetic neutrons hits iron and makes more massive elements like gold, silver and uranium. Supernova also make cosmic rays. These rays may have hit genetic material on the earth contributing to steady mutations.
A supernova 50 ly away from us would wipe all life out. 100 ly away would cause damage. The closest candidate is Spica 260 ly away. Records tell us supernova occur in our galaxy every 25 to 100 years.
A Supernova in the Large Magellanic cloud. A small galaxy near us. It could be seen with the naked eye 160,000 ly away. SN 1987a discovered in 1987. It formed 10 million years ago with a mass of 20 solar mass spectral type O.
After a supernova all that is left is the densest object in the universe. It s gravity 10 to the 11 th power greater that the Earth. It is 95% neutrons and is a neutron star.
Antony Hewish designed a detector.
Jocelyn Bell a grad student.
She detected a pulse that occurred every 1.33728 seconds. They are called pulsars short for Pulsating Radio sources. These pulses are from 1/1000 of a second to every 10 seconds.
Nothing could be visibly seen with these objects till the crab nebula.
Only a dense small object would have enough angular momentum to flash that fast. The beam comes out if its magnetic poles. The only place trapped particles could escape.
We think 100 million neutron stars are in our galaxy. Young pulsars have fast periods and old pulsars long periods.
We now think half of the stars develop in binary systems. This transfer of mass can be dramatic when one receiving is a white dwarf or neutron star. The mass transfer to a white dwarf builds up a layer of H that heats up and explodes causing a nova.
If too much material goes over to the white dwarf to fast it can go past the Chandrasekhar limit of 1.4 solar masses. The core will heat up and collapse then explode in a supernova destroying the white dwarf.
This is a type Ia supernova.
Sometimes material transfer goes to a neutron star. These are called x-ray bursts.
Some pulsars are extreme in speed. They are part of binary systems spinning 1000 times a second. Some are fast from eating the mass of their companion. These are black widow pulsars.
Ways stars die based on the amount of mass they have near the death. < 1.4 solar masses = white dwarf. 1.4 3 solar masses = Neutron stars. > 3 solar masses = the next chapter.