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
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