life cycle of a star

Nebula

=cloud of dust and gas

Protostar

1. formed when dust and gas are pulled together by gravity.

2. density increases, particles collide, temperature increases

Main Sequence Star

1. when temperature high enough, nuclear fusion (H→ He) begins

2. releases energy so star core hot

3. outward pressure (from thermal expansion due to nuclear fusion) balances inwards force (due to gravity)

4. so long stable period of billions of years

5. heavier star= shorter life

Red Giant (lower mass)

1. eventually H in core runs out

2. force due to gravity>pressure from thermal expansion

3. star compressed until dense and hot enough that outer layer expands (due to energy and pressure)

4. star red as surface cools

White Dwarf (lower mass)

1. star unstable so ejects outer layer (dust and gas)

2. hot, dense, solid core remains

Black Dwarf (lower mass)

white dwarf cools so turns black

Red Supergiant (higher mass)

1. eventually H in core runs out

2. force due to gravity>pressure from thermal expansion

3. star compressed until dense and hot enough that outer layer expands (due to energy and pressure)

4. star red as surface cools

Supernova (higher mass)

1. star glows brightly as it undergoes fusion of heavier elements

2. expands and contracts rapidly (balance shifting between gravity and thermal expansion)

3. energy eventually released in shockwave (=supernova)

Neutron Star (higher mass)

1. exploding supernova expels outer layer (dust and gas)

2. very dense core remains

Black Hole (highest mass)

1. star collapses inwards

   = super dense point that light cannot escape from