Star formation
- The Beginning
- Stars form in dense concentrations of gas and dust called molecular clouds.
- The regions in which they form are extremely cold, just above absolute zero.
- Because of these temperatures, gases clump and are very dense.
- When the density reaches a certain point, stars begin to form.
- Protostar
- A protostar is a clump of gas that has broken free from the other parts of the cloud’s core.
- The gas releases heat and the temperature and pressure in the core of the protostar goes up.
- If a protostar has enough matter, the central temperature of the star can reach up to 15 million degrees centigrade.
- If it reaches this temperature, nuclear reactions begin in which hydrogen fuses to form helium.
- At this point, the star begins to release energy, effectively stopping it from contracting and causing it to shine. Now it is a main sequence star.
- Main Sequence Star
- A main sequence star is a star that is fusing hydrogen to form helium. About 90% of stars are main sequence stars.
- The life span of a main sequence star is dependent upon inner temperature and higher or lower mass.
- Eventually, though, the hydrogen is burned through to the core, and the star reaches the end of its life cycle.
- After the End
- So, the star burns out. What next? It just disappears? Wrong!
- After the hydrogen is gone, smaller stars collapse into white dwarfs.
- Larger stars, however, have a much different process. Their outer layers inwardly collapse until their outer layers are hot enough to fuse into carbon, thus releasing a pressure that expands the star, turning it into a red giant.
The video below shows basically what I have said here (and a little more!). It should help you visualize the process that's happening.
Here's a little quiz to see if we got our point across.
1. Where do stars form?
1. Where do stars form?
2. When a star releases energy, stopping it from contracting and causing it to shine, it becomes a:
3. What is a clump of gas that has broken free from the other parts of the cloud's core.
4. What percentage of stars are main sequence stars?
5. What happens when a large main sequence star burns up all of its hydrogen?