Stars and their lives
An average star is born in a nebula, a cloud of gas and dust that contains hydrogen and helium. Gravity causes this dust and gas to bind together and then, a star is formed. The star begins to burn, fuelled by nuclear fusion. The life of a star depends on the star’s mass and the colour of the star depends on the temperature. If the core of the star does not reach the required high temperature, it will be a brown dwarf, a ‘failed star’. But if it does reach the needed temperature, it will evolve into a protostar, the core of this star is 15,000,000°C. As the protostar grows, it releases energy and causes it to shine. When the core is hot enough for the helium to fuse to form carbon, the outer layers start to expand, cools down and it will shine less brightly, this is a red giant. The helium in the core of the star will then run out, and the gassy outer layer will drift off. What is then remaining in the core becomes a white dwarf and when the star stops shining, it will be a black dwarf.
Sometimes, the star is bigger in size after being a protostar. And so instead of evolving into a red giant, it will be a red supergiant. Red supergiants can become blue supergiants if their nuclear reactions slow down. In the next million years, the nuclear fuel in the star will eventually run out, and the core will collapse, causing a massive explosion that will release a large amount of energy. This is called a supernova. Once the star collapses, a neutron star can be formed (a dense star mostly made out of protons and have a strong magnetic field.) And if the neutron star rotates, it is a pulsar. Sometimes, some bigger stars can collapse into a black hole, a dense “hole” that has a great gravitational pull.