28.3 Life Cycles of Stars

Stars are born out of great clouds of gas and dust They mature, grow old and die They may produce new clouds of dust and gas And planets The more massive a star the shorter the life span

Hertzsprung - Russell Diagram A graph that plots luminosity against surface temperature The HR Diagram is much like the same thing as producing a graph of people’s height vs. weight.

Main Sequence Most stars 90 % Extends from the hot, bright, bluish stars in the upper left to cool, dim, reddish stars in the lower right Vary in temperature, magnitude and lifespan

Giant Stars – 10 – 100 x’s diameter of Sun Cool, luminous stars. – Luminous because of large size.

Supergiants – 100 x’s diameter of sun Bright due to size even though cool

White Dwarfs HOT but faint stars Near end of life Once Red Giants The surface temperatures of these stars are very hot, but since they are so small they are not very luminous

White Dwarfs Supergiants Red Giants Main Sequence Absolute Magnitude Bright Dim Luminosity O B A F G K M Early Types Hot Late Types Cool

Birth of a Star Nebula condenses due to outside force Force compresses gas and dust and the particles move closer together due to gravity Become – Denser – Hotter If large enough nebula will begin to glow Protostar is born

Death of Sun like star

Death of Massive Star

Remnants of Stars Supernova – explosion of star – Neutron star – Gravity crushes atoms electrons into nucleus – 20 Km diameter – Trillion x’s as dense as sun

Pulsar Rapidly spinning neutron star Gives off radio waves in bursts Like lighthouse light

Black Holes Remnant of a star at least 15 Solar Masses Packed into 30 Km diameter Gravitational force so strong light cannot escape Give off x-rays when atoms are ripped apart Gravity of millions or billions of suns