Question: What is the life-cycle of a star?

Affelia Wibisono answered on 12 Mar 2019:

The life cycle of stars describe how they’re made, what they do, how they die and what happens afterwards. Stars are made in nebulae which are clouds of gas and dust. Something like an exploding nearby star would stir up the gas and dust and they start to clump together. The clump gets bigger and that attracts more material because of gravity. Eventually the clump of gas gets really hot and it starts to shine and becomes a star. Smaller like our Sun can keep on shining for many billions of years. The Sun is about halfway through its 10 billion year lifetime. Eventually, these stars will start to run out of hydrogen fuel (the thing that powers the star and keeps it shining) and they will expand and cool down until they’re only a few thousand degrees Celsius. They will change their colour from yellow to red. We call these stars red giant stars. An example of a red giant star is Aldebaran, the eye of Taurus.

Afterwards these stars will lose its outer atmosphere and become a planetary nebula. One of my favourites is the Helix Nebula.

The core of the dead star is in the middle and is called a white dwarf star. It heats up the material that once made up the star’s atmosphere and makes them glow different colours depending on what gas it’s made of. The white dwarf star will then eventually cool down and will stop glowing.
Very massive stars use their fuel much quicker – over a few million years. When it starts to run out of fuel it’ll become a super red giant star. The star Betelgeuse which is in the constellation of Orion, is a super red giant star. These stars die violently in a supernova, throwing all of its material out into space. Betelgeuse is about to go supernova anytime soon. We just don’t know exactly when. It could happen tonight or in a thousand years. But when it does go supernova it’ll be so bright that you could see it during the daytime! So I guess we’d better keep our eyes on it. The cores of these stars become very packed together – imagine something that is made up of the same amount of stuff as the Sun squashed into a sphere that’s 20 km wide. This is what makes them so dense. We call these types of stars neutron stars. They’re often spinning and release jets of radiation – but don’t worry there aren’t any that are close enough to the Earth to be dangerous. We call these pulsars, short for pulsating stars. There’s a pulsar in the middle of the Crab Nebula.

If the original star was really, really massive then its core would be so dense that its gravitational pull would be enough to stop light from escaping. This is what a black hole is! We call it the life-cycle of stars because all of the material that was released by the dying stars, whether they were big or small, can then be used to make new stars and so the cycle can begin again.