15-3

1. 15-3 The Lives of Stars

2. Studying the Lives of Stars • Astronomers must study stars at different stages to study the lives of stars

3. A star is born • Stars are born in nebula (a vast cloud of gas and dust) • Gravity pulls gas together • When nuclear fusion takes place a star is born • The youngest stars are called protostars

4. Lifetimes of Stars • How long a star lives depends on it’s mass • The more mass a star has the shorter it will live

5. Red Giant Stars • As the mass of a star’s core decreases, so does its gravity • The core is no longer able to maintain the stars small size, so it expands into a red giant.

6. Deaths of Stars • When a star runs out of fuel it turns into a white dwarf, a neutron star, or a black hole. • White dwarfs • The core of a red giant star whose outer layers have dissipated (spreads out) • Size of earth, with same mass as our sun • Turns into a black dwarf when fuel runs out • Neutron Stars • Left over from a supernova • Supernovas are giant explosions from dying stars • Left over core is called a Neutron Star • 20km across • three times the mass of our sun

7. Death of Stars Continued • Black Holes • Leftover from a supernova of a very massive star • 5 times the mass of the sun packed into a sphere the size of a marble • Gravity so strong nothing, not even light, can escape • Quasars are black holes millions of light years away that shine very bright (galaxies with black holes in the center)