2. STELLAR EVOLUTION

3. What is a star?
A star is a huge ball of hot gas, held together by its own gravity.
Most of the gas is hydrogen - helium is the second most common.
The gravity of the huge ball of gas forces the atoms together so strongly they fuse together.
This nuclear fusion gives off energy- mostly heat and light.

4. A STAR IS BORN New stars form from huge clouds of dust.
A new generation of stars is currently forming in these pillars of dust.

5. balanced forces
The gravity of all that matter pulls in toward the center.
The heat generated by the nuclear fusion pushes out.
Balanced forces give a stable star.

7. Main Sequence Star
The hydrogen in the core is the fuel for the nuclear reaction that is the source of the star’s energy.

8. Main Sequence Stars
Energy source is the fusion of hydrogen to form helium.
Can be as small as 1/10 mass of the sun
Can be as big as 60 times the mass of the Sun

9. Red Giant The hydrogen fuel supply runs low.
Helium fusion begins in the core.
Outer layers expand.

10. Main sequence star death
Fusion fuel is used up
star collapses
ejects dust and gas cloud
remains form a white dwarf star
life cycle is about 10 billion years

13. The Death of an Evolved, Massive Star
The iron core will not ignite to induce further nuclear burning as has happened earlier to the helium, carbon-oxygen, and other cores.
Iron fusion doesn’t release energy.

14. supernova

15. Crab nebula
This is the dust cloud visible today that is left from a supernova in 1054.

16. Supernova remnant Remnants release X-rays
contain dust with wide variety of elements

17. remnants

18. BLACK HOLES A black hole could form if a star
collapsed into one small area.
All the matter, and all the gravity
of the star
would be in an area so small,
even light would not escape.

19. Size comparison