Post on 15-Jul-2015
transcript
Life and Death of Stars
Where do stars go when they die?
Review of Birth
Fusion: Hydrogen fuses into Helium due due to pressure. Its own gravity causes
the pressure and collapse but energy fromfusion pushes back against the collapse.
And we
have a star.
Main Sequence
Stars spend most of their time just
converting hydrogen to helium.
Death of a Star
Stars will run out of hydrogen asapproximately
fM/L
fM is the fraction of the total mass of the star available for burning and L is theLuminosity of the star in its main sequence lifetime.
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.
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 kahnacademy notes
https://www.youtube.com/watch?v=r35EooK-vFs
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.
6. The carbon core will eventually cool and become a white dwarf, the dense dim remnant of a once bright star.
Pair of White Dwarfs
http://www.nasa.gov/vision/universe/starsgalaxies/collide_whitedwarf.html
https://www.youtube.com/watch?v=EdYyuUUY-ncKahn Academy notes
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.
Supernova
http://chandra.harvard.edu/photo/2010/type1a/type1a_merger_trigger.m4v What does a supernova look like?
https://www.youtube.com/watch?v=yICdhm3GmT8 What does a supernova sound like?
https://www.youtube.com/watch?v=UhIwMAhZpCo Kahn Academy notes
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.
Quasars
• https://www.youtube.com/watch?v=4LmIyMyAuN0 kahn academy notes
• https://www.youtube.com/watch?v=PX_XSnVWlNc note correction
• https://www.youtube.com/watch?v=GT-HTJ0HB1I most distant quasar
https://www.youtube.com/watch?v=U72XK0giMzU
Pulsars
• A type of neutron star that rotates very fast.
• http://chandra.harvard.edu/photo/2014/igrj11014/spacescoop_igrj11014_sm_web.mov
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=DxkkAHnqlpY kahn academy notes
https://www.youtube.com/watch?v=3sBXdiN0dy4 Early speculation.
Black Holes
• https://www.patreon.com/creation?hid=308154 Can light orbit a black hole?
• https://www.youtube.com/watch?v=PHiFJ4sKFbs How do you kill a black hole?
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
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/forstudents/5-8/features/what-is-a-black-hole-58.html#.VPilNeEsCDk