Life Cycle of Stars

• Nebula• hundreds of light

years in size• contract under gravity

http://en.wikipedia.org/wiki/Image:Horsehead-Hubble.jpg

Life Cycle of Stars

• Protostar• radiate heat from

gravitational contraction

http://en.wikipedia.org/wiki/Image:Herbig-Haro_object_HH32.jpg

Life Cycle of Stars

• Main Sequence Stars• fuse hydrogen into

helium (releases energy)

• hydrostatic equilibrium

• most of star’s life spent on main sequence

http://www.oswego.edu/~kanbur/a100/images/hydrostaticequilibrium.jpg

Life Cycle of Stars

• hydrogen depleted in core

• core composed of helium

• core contracts and heats, outer layers expand and cool

• star leaves main sequence

http://personal.tcu.edu/~pmarcum/courses/P2083/handouts/starevol1_lect.html

Life Cycle of Stars

• low mass stars turn into Red Giant Stars

• helium fuses into carbon

• very low mass stars (<1/4 solar mass) do not fuse helium

http://fas.org/irp/imint/docs/rst/Sect20/Arcturus.jpg

Life Cycle of Stars

• helium depleted in core

• core contracts and heats, outer layers expand and cool

• temperatures not hot enough to fuse carbon

• star leaves red giant region

• unstablehttp://personal.tcu.edu/~pmarcum/courses/P2083/handouts/starevol1_lect.html

Life Cycle of Stars

• Planetary Nebula• outer layers expelled

into space• small, dense, hot core

exposed

http://en.wikipedia.org/wiki/Image:Eskimo_nebula_%28cropped%29.jpg

Life Cycle of Stars

• White Dwarf• electron degeneracy

pressure• cool over time

http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit3/Images/WhiteDwarf.gif

Life Cycle of Stars

• high mass stars• evolve quickly• turn into Supergiant

Stars

http://abyss.uoregon.edu/~js/images/Aldebaran.jpg

Life Cycle of Stars

• Supergiant Stars are massive enough to produce temperatures and pressure high enough to fuse heavier elements in successive stages

• iron core is built up

http://en.wikipedia.org/wiki/Image:Evolved_star_fusion_shells.svg

Life Cycle of Stars

• iron cannot fuse into heavier elements

• iron core collapses• star explodes • known as a

Supernova

http://en.wikipedia.org/wiki/Image:Crab_Nebula.jpg

Life Cycle of Stars

• Neutron Stars• remnant after

supernova is less than 3 solar masses

• neutron degeneracy pressure

• fast rotating• radiate beams of

energy• known as Pulsars

http://upload.wikimedia.org/wikipedia/commons/1/1d/Vela_Pulsar_jet.jpg

Life Cycle of Stars

• Black Hole• remnant after

supernova is greater than 3 solar masses

• neutron degeneracy pressure is overwhelmed

• light cannot escape

http://en.wikipedia.org/wiki/Image:BH_LMC.png