2. Review of Birth
Fusion: Hydrogen fuses into Helium due
due to pressure. Its own gravity causes
the pressure and collapse but energy from
fusion pushes back against the collapse.
And
we
have a
star.
4. Death of a Star
Stars will run out of hydrogen as
approximately
fM/L
fM is the fraction of the total mass of
the star available for burning and L is the
Luminosity of the star in its main
sequence lifetime.
5. Red Giant
After a low mass star
like the Sun exhausts
the supply of hydrogen
in its core, there is no
longer any source of
heat to support the
core against gravity.
Hydrogen burning
continues in a shell
around the core and
the star evolves into a
red giant.
6. Meanwhile,
1. The core of the star collapses under gravity's pull until it
reaches a high enough density to start burning helium to
carbon.
2. After the helium burning phase, star becomes a red giant.
3. At this stage, the Sun will have an outer envelope
extending out towards Jupiter.
https://www.youtube.com/watch?v=kJSOqlcFpJw kahn
academy notes
https://www.youtube.com/watch?v=r35EooK-vFs
7. 4. the Sun will lose mass in a powerful wind.
Eventually, the Sun will lose all of the mass in its
envelope and leave behind a hot core of carbon
embedded in a nebula of expelled gas.
5. Radiation from this hot core will ionize the
nebula, producing a striking "planetary nebula",
much like the nebulae seen around the remnants of
other stars.
8. 6. The carbon core will eventually
cool and become a white dwarf, the
dense dim remnant of a once bright
star.
9. Pair of White Dwarfs
http://www.nasa.gov/vision/universe/starsgalaxies/collide_whitedwarf.html
https://www.youtube.com/watch?v=EdYyuUUY-nc
Kahn Academy notes
11. Death of a Massive Star
• Massive stars burn brighter and perish more dramatically than most.
When stars ten times more massive than Sun exhaust the helium in the
core, the nuclear burning cycle continues. The carbon core contracts
further and reaches high enough temperature to burn carbon to oxygen,
neon, silicon, sulfur and finally to iron. Iron is the most stable form of
nuclear matter and there is no energy to be gained by burning it to any
heavier element. Without any source of heat to balance the gravity, the
iron core collapses until it reaches nuclear densities. This high density core
resists further collapse causing the infalling matter to "bounce" off the
core. This sudden core bounce (which includes the release of energetic
neutrinos from the core) produces a supernova explosion. For one brilliant
month, a single star burns brighter than a whole galaxy of a billion stars.
Supernova explosions inject carbon, oxygen, silicon and other heavy
elements up to iron into interstellar space. They are also the site where
most of the elements heavier than iron are produced. This heavy element
enriched gas will be incorporated into future generations of stars and
planets. Without supernova, the fiery death of massive stars, there would
be no carbon, oxygen or other elements that make life possible.
13. Neutron Star
Neutron stars are
created when giant
stars die in supernovas
and their cores
collapse, with the
protons and electrons
essentially melting into
each other to form
neutrons.
14. Quasars
• https://www.youtube.com/watch?v=4LmIyMy
AuN0 kahn academy notes
• https://www.youtube.com/watch?v=PX_XSnV
WlNc note correction
• https://www.youtube.com/watch?v=GT-
HTJ0HB1I most distant quasar
https://www.youtube.com/watch?v=U72XK0giMzU
15. Pulsars
• A type of neutron star that rotates very fast.
• http://chandra.harvard.edu/photo/2014/igrj1
1014/spacescoop_igrj11014_sm_web.mov
16. Black Holes: The End of Space and
Time
Black holes are the cold remnants of former
stars so dense that no matter—not even
light—is able to escape their powerful
gravitational pull.
https://www.youtube.com/watch?v=Dxk
kAHnqlpY kahn academy notes
https://www.youtube.com/watch?v=3sBXdiN0dy4 Early
speculation.
18. Summary
• Ordinary Star is born through fusion – exists
as main sequence star where it burns
hydrogen into helium – runs out of fuel and
becomes red giant where it expands – next
stage is nebula and stellar winds take most of
it – finally it becomes a white dwarf
• Massive stars – main sequence – super giant –
supernova – neutron star
19. Summary Continued
• Or maybe the result of a star’s death is
a black hole:
• What, How big, How do, How powerful,
• Quasars go back to the beginning of
time.
• http://www.nasa.gov/audience/forstude
nts/5-8/features/what-is-a-black-hole-
58.html#.VPilNeEsCDk
