• Question: how can a neutron star be reborn of the remains of a normal star?

    Asked by 10jazminbradford to Evan on 14 Jun 2011.
    • Photo: Evan Keane

      Evan Keane answered on 14 Jun 2011:

      Great question! Ok, this is how it works.

      Stars are made almost entirely of hydrogen. If you look at a periodic table (maybe on the wall in your science lab?) you will see that hydrogen is the lightest element. In the centre of stars it is very crowded and hot, and the hydrogen atoms get pushed together. If you get two hydrogen atoms and squeeze them together they “fuse” and make a helium atom. Check the periodic table – helium is the next element. This “fusion” releases energy and this energy is what is used to make the star shine! This is how stars live.

      What happens when all the hydrogen is turned to helium? Well then the helium atoms get squished together. If you get three helium atoms and “fuse” them, you get a carbon atom, and some more energy is released. Great – this energy can be used to keep the star shining. After the helium all turns to carbon, the carbon atoms can be fused to make nitrogen, and then oxygen, and then silicon and so on. This is how a star gets old.

      But when the centre of the star has done this many times so that all that is left is iron (like our zone name!) there is a problem. Combining two iron atoms WILL NOT release energy. Uh oh. The star is out of energy. The energy from the fusion was acting outwards and keeping the star together as the strong force of gravity acted inwards. But now we only have iron and can fuse no more. So gravity is acting in and nothing is acting out! The star is about to die!

      The outer layers fall towards the centre of the star and squish the iron core A LOT! Once it can’t squish it any more the outer layers bounce off the squished core and are shot out into space in a huge explosion. This is what we call a supernova. They look cool. Here is a picture of the “the Crab” which is a supernova that happened in 1054 (ya, ages ago but when it did it was so bright you could see it during the day!).

      http://apod.nasa.gov/apod/ap051202.html

      All that material flying out is the outer layers of the star that have been shot out into space. The core of the star which was squished down to very small size is a neutron star! And neutron stars can be pulsars and emit a lighthouse beam of light. Here is another picture of the Crab but now an X-ray picture.

      http://apod.nasa.gov/apod/ap061026.html

      Can you see the pulsar in the middle in this one? 🙂

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