Transcript Life Cycle of Stars

• 1st Step:
– Stars form from nebulas
• Regions of concentrated dust and gas
– Gas and dust begin to collide, contract and heat
up
• All due to gravity
• 2nd Step:
– As nebula contracts, a small star is formed
• Called a protostar
– Eventually, the protostar will begin nuclear
fusion
• Hydrogen protons attract to each other
– Strong nuclear force
– Fusion begins
• Necessary for stars to survive
• 3rd Step:
– Star joins the main sequence
• 90% of stars are here
• Nuclear fusion = Hydrogen into Helium
• Mass of star determines location on main sequence
• Beginning of the End:
– Stars begin to die when they run out of
hydrogen
• Gravity begins to take over
– Star begins to shrink; outer core of hydrogen
begins to fuse
• Star gets bigger
• Beginning of the End:
– When star gets bigger, it cools down
• Red giant
– Eventually, star can fuse helium into other
elements
• Carbon, oxygen, and other heavier elements
• Beginning of the End:
– Once star runs out of “fuel”, star shrinks under
its own gravity
– Turn into a white dwarf, neutron star, or black
hole
• Death of Stars:
– What stars end up as depend on mass
– Low and Medium mass stars
• Planetary nebula --------- white dwarf
– High mass stars
• Supernova --------- neutron star or black hole
• Death of Stars: Low and Medium Mass
Main Sequence Star
Red Giant
Planetary Nebula
White Dwarf
• Death of Stars: High Mass
Main Sequence Star
Red Super Giant
Supernova
Neutron Star
Black Hole
• What is a Black Hole???
Black
Holes Info
Sheetthat not even
– An object
so massive
and dense
light can escape its gravity
– The end result from a supernova of a star that
has a mass greater than 3x the sun
Do Do black holes live forever?
•
Since nothing can escape from the gravitational force of a black hole, it was long thought that
black holes are impossible to destroy. But we now know that black holes actually evaporate,
slowly returning their energy to the Universe. The well-known physicist and author Stephen
Hawking proved this in 1974 by using the laws of quantum mechanics to study the region close
to a black hole horizon.
•
The quantum theory describes the behavior of matter on the smallest scales. It predicts that tiny
particles and light are continuously created and destroyed on sub-atomic scales. Some of the
light thus created actually has a very small chance of escaping before it is destroyed. To an
outsider, it is as though the event horizon glows. The energy carried away by the glow decreases
the black hole's mass until it is completely gone.
•
This surprising new insight showed that there is still much to learn about black holes. However,
Hawking's glow is completely irrelevant for any of the black holes known to exist in the
Universe. For them, the temperature of the glow is almost zero and the energy loss is negligible.
The time needed for the black holes to lose much of their mass is unimaginably long. However,
if much smaller black holes ever existed in the Universe, then Hawking's findings would have
been catastrophic. A black hole as massive as a cruise ship would disappear in a bright flash in
less than a second.
http://hubblesite.org/explore_astronomy/black_holes/encyc_mod3_q10.html
• High Mass Stars:
– Mass greater than 3x our sun
• Create high mass elements such as iron
– Neutron Star
• Formed if remaining star < 3x sun’s mass
– Black Holes
• Formed if remaining star > 3x sun’s mass
• As fusion begins to slow down, the core of
the sun will contract
• Temperature in the core will rise
• The outer layers of the sun will expand,
consuming the inner planets
• Sun will become a Red Giant
– Core of the sun will begin to fuse helium into
larger elements such as carbon and oxygen
– Continuing over the next 100 million years…
• Core will become entirely carbon and oxygen
• Core will contract
• Outer layers will expand
– Outer layers will form a planetary nebula
• Core of sun will become a white dwarf