(c) Stellar evolution
What is the milky way?
The name of our galaxy is the milky way. It is a spiral galaxy.
What is Galaxy?
Due to high gravitational force many stars form a group called a galaxy.
How does the colour of stars tell us about their temperature?
- A very hot star emits more blue in its spectrum and therefore looks blue,
- A medium star like our sun looks yellow and,
- A cooler star appears red.
What are the two factors that brightness of a star depends on?
- The two factors are:
- The distance between a star and the earth.
- The luminosity of the star.
Describe the birth of a star.
Dust and gas particles are drawn together by gravitational forces. Compression of these particles causes an increase in temperature. Due to high temperature nuclear reactions begin. When nuclear fusion reaction starts, hydrogen nuclei join together to make a large nuclei. Huge amount of energy is released in the form of heat and light, therefore, it forms a hot ball of gas which is a young star. Unused material around the young star begins to group together to form planets, moons and comets which orbit the star.
What happens to a star after the stable period?
- The star expands and becomes cool.
- It forms a red giant.
- The star collapses and the temperature is increased.
- Due to high temperature, the star changes colour.
- It emits more blue and white light.
- It changes into a white dwarf star.
- The white dwarf star cools and forms a black dwarf star.
What is a supernova?
A star which is much larger than our sun expands into a large, red supergiant. After the stable period, then it contracts and becomes unstable. It explodes throwing dust and gas into space to form a new stellar nebula. This exploding star is called supernova.
What is a neutron star?
After the explosion to form supernova of a large red giant star, remaining dust and gas particles form a very dense star called neutron star.
What is black hole?
If the neutron star has a mass of five times greater than the sun or more, it collapses further to become a black hole.