Lives of StarsSection 3

Nebula

• Large cloud of gas and dust spread out in an immense volume

• All stars are born in a nebula, large cloud of gas and dust.

Protostar

• Gas and dust begin to collect due to gravity.

• Once enough material has formed together, a protostar is created.

• This is the beginnings of what will become a star. A star is born when nuclear fusion begins.

Lifetimes of Stars

• Like automobiles burning through their gas, the length a star lives depends on its mass.

• Larger, more massive stars live shorter while less massive stars live longer.

Deaths of Stars

• As the star runs out of fuel, its core shrinks and gets hotter.

• As it does so, it heats the gases surrounding it which causes the outer layers to expand.

• The star will then become a black dwarf or black hole dependent upon its starting mass.

Less Massive Stars

Nebula Protostar

Low-mass or medium-mass star

Red Giant Planetary Nebula

White Dwarf Black Dwarf

Medium Sized Stars

• Medium sized stars are the most common in the universe. An example is our sun. Medium size stars are 10 times more massive than a red dwarf

Red Giant

• 10-100 times the size of our sun. It shines red and it is about 3000oC.

Planetary Nebula

• After the red giant, the star will create a planetary nebula, which is the glowing gas of the outer layers as they expand away from the core.

White Dwarf

• The only thing that remains after is the core of the star, a very hot dense, white dwarf. After billions of years this will eventually cool to become a black dwarf.

Greater Mass Stars

• Nebula Protostar

High-mass star Supergiant

Supernova Neutron Star

Black Hole

Red Supergiant

• High mass stars quickly evolve into brilliant supergiants.

Supernova

• All massive stars will explode in a supernova.

Supernova Images

Neutron Stars

• The lower mass high mass stars will instead become neutron stars.

• Neutron stars spin rapidly and emit radio waves.

Black Holes

• However, only the most massive will become black holes.

• Remains of a supernova which contains enough gravity that light cannot escape

• After a very massive star dies in a supernova explosion, more than 5 times the mass of the sun may be left

• The gravity of this mass is so strong that the gas is pulled inward, packing the gas into smaller and smaller space.

Black Holes

• Not able to detect a black hole directly because no light, no radio waves, or any other form of radiation can ever get out of a black hole

• Detect black hole indirectly• Gas near a black hole is pulled so strongly that it

revolves faster and faster around the black hole• Friction heats the gas up• Astronomers can detect X-rays coming from the

hot gas and infer that a black hole is present

                                                                                    

Reminders

• Only stars with more than 40 times the mass of the sun form black holes when they die

• Other high mass stars become neutron stars when they die

• When a star begins to run out of hydrogen, it can become a red giant or supergiant

• United Streaming Video

• Brain Pop Segment