19. Life cycle of stars [Autosaved].pptx

Life cycle of stars

1. 19. Life Cycle of Stars

2. Our solar system is situated in a similar galaxy.

3. Properties of star Stars are gigantic spheres of hot gases. At night, we can see about 4000 stars with our naked eyes . 3. Sun is an ordinary star among them, The reason all sun an ordinary star is that even though it appear to be larger than all other stars in the sky Because it is nearer to us. 4. There are billions of star which have higher or lower mass size and temperature than those of the sun .

4. Mass 2x 10 30  kg Radius 695700 km Surface temperature 5800 K Temperature at centre 1.5 x 10 7 K age 4.5 x 10 9 K Properties of the sun:

5. The mass of the sun is about 3.3 lakh times that of the earth and its radius is 100 times that of the earth. The age of the sun and other stars which can be around between few million and few billion year. The sun have remained unchanged over its lifetime i.e. the past 4.5 billion years and properties will change in further after 4.5 billion years. Comparison of sizes of different stars

6. Birth of Stars (Formation of stars) Huge clouds of gas and dust are present in the empty spaces between stars in a galaxy. These are called interstellar clouds . The size of interstellar clouds is few light years. A light year is the distance travelled by light in one year. One light year is equals to 9.5 trillion kilometers.( 9 .5 x 10 12 km) The speed of light is 3,00,000 km/s . Due to some disturbances the clouds start contracting. The density increases and the temperature also increases with a dense sphere of hot gas formed from the cloud. Because of this, the gas sphere becomes self-luminous and a star is formed.

7. Picture of interstellar clouds taken by the Hubble space telescope.

8. A large cluster of stars. Most of these stars have formed from a single interstellar cloud. Then , why doesn’t the hot gas in the stars disperse in space ? The answer is Gravitational force . The properties of the sun remained unchanged for the last 4.5 billion years because of the gravitational force. The gravitational force between the gas particles of the star keeps these particles together and the pressure of the hot gas which disperses the gas are balanced, then the star remains stable. The gravitational force is acting inwards, towards the center of the star and the gas pressure act outwards , i.e. away from the center of the star. Stability of stars

9. Evolution of Stars Evolution of star means change in its properties with time resulting in its passing through different stages. Stars evolve very slowly for most of their lifetime, As stars are continuously emitting energy, their energy is constantly decreasing. The reason for the evolution of stars is the burning of fuel and therefore the decrease in the amount of fuel in their center. Higher the mass of the star higher is the number of fuels used. During this a lot of changes occur in the star.

10. Three end stages of stars White dwarf It is an end stage for stars having initial mass less than 8 times mass of the sun. It is small size and white appearance. White dwarf is formed after explosion of red giant star. M star < 8 M sun Neutron star It is an end stage for stars having initial mass less than 8 and 25 times mass of the sun. It is completely made up of neutrons. Neutron star is formed after supernova explosion of a supergiant star. 8 M sun < M star < 25 M sun Black hole It is an end stage for stars having initial mass greater than 25 times mass of the sun. It is termed because it absorbs all light falling on it and it can absorb anything in it. Black hole is formed after explosion of a supergiant star. M star > 25 M sun ( M star = Mass of a star ) ( M sun = Mass of a sun)

11. Supernova Explosion

12. White Dwarfs

13. Neutron Stars

14. Black Hole

15. How we see the solar system work How actually the solar system work

16. The End