• Question: Are black holes and neutron stars the only two things that can be created when a star dies?

    Asked by anon-252841 to Ry on 4 May 2020.
    • Photo: Ry Cutter

      Ry Cutter answered on 4 May 2020: last edited 4 May 2020 10:39 pm

      There are three main channels (and a bonus one cause I love dead stars!) Each one is based on how much the star weighs.
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      Black-holes form when a massive star (more than 30 times our sun) dies. When fusion stops, it can no longer fight gravity and collapses in on itself. This is called a core-collapse supernova. The gravitational squishing is so intense that all of the matter gets pushed into a single point, making a black hole!
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      Neutron stars are the same, but their alive star (the progenitor), weighs a lot less. Between 8-25 times the mass of the sun. (Anything between 25 and 30 can become either a black-hole or a neutron star, it depends how much material the star keeps as it collapses!) Because the star doesn’t weigh so much, it’s gravitational collapse is not as severe. This means instead of being smushed into a single point, all the subatomic particles are pushed closely together, into about a 15km sphere! The protons and electrons are forced together to make neutrons, hence neutron star. The material is so dense a single tablespoon would weigh more than mt Everest!
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      White dwarfs are what stars less than 8 times our sun become. When these stars run out of fuel, they expand into what we call a red-giant. Here, carbon and oxygen are made that eventually settle into a crystal like structure until the star runs out of fuel. This is why we call white dwarfs hot diamonds! These dead stars weigh about the same as the sun, but are the size of Earth.
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      Another way you can kill a star is by sucking up it’s fuel! These are called spider systems (though zombie system would be more fitting!). This requires one dead star (a neutron star) eating up another. As the fuel of the poor star gets pulled in, it looses mass, until eventually it cannot fuse hydrogen anymore. The star is dead! This leaves what we call a degenerate brown dwarf. Not much study has been done into these stars just yet, but we think they have some very interesting structures inside them!
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      I loved this question!
      Ry

Comments

  • Photo: anon-252841

    anon-252841 commented on :

    Thank you, this is really interesting.

  • Photo: Susan

    Susan commented on :

    To add to Ry’s answer, in fact MOST stars end up as white dwarfs: to become a neutron star or a black hole the star has to start off with at least 8 times the Sun’s mass, and these are very uncommon stars (<1% of all stars).

    Also, there are two kinds of white dwarfs. The most common kind today are the ones Ry describes, with masses of between 0.5 and 1.4 times the Sun's mass and made of extremely compressed carbon and oxygen. These are the remnants of stars that went through two fusion cycles (hydrogen to helium, and helium to carbon) but did not fuse heavier elements. However, the most common type of star, M dwarfs, are not massive enough to attain the core temperatures needed to fuse helium, and the will eventually end up as less massive (0.1 to 0.5 times the Sun's mass) helium white dwarfs. We do not see these tofay because M stars are incredibly long-lived: they fuse their hydrogen very slowly, and will not run out for trillions of years, so every M dwarf ever formed in the history of the universe is still on the main sequence. In the far future, however, in the Milky Way's extreme old age, helium white dwarfs will be the most common type of dead star.