[Under Construction]



Life Cycles of Stars


Key Terms:

Notes:  (28-3)

Just like people, stars are born and they eventually die.  The begin as large clouds of nebular dust and end as either burned out masses or violent explosions.  These explosions produce the materials for the production of new stars.

H-R Diagram (Hertzsprung-Russell)

plots the temperature of stars against their luminosity
2 main groups
main sequence stars
~ 90% of the known stars fall into this category
band runs from the upper left to the lower right
our sun is located in the middle of this band
giant stars
largest and brightest stars
located above the main sequence stars
contains the supergiants
most likely to undergo a supernova explosion
white dwarfs
are the remaining cores of previously burned out red giants 
are stars at the very end of their life cycles

(www.aw.com/bc/info/bennett/ images/hrdiagram.jpg)

Birth of a Star
Stars begin as clouds of dusts called nebula
made of mostly H & He gases and small dust particles
gases begin to condense in the presence of an outside force (shock wave)
the condensing gas increases in density and temperature and is now considered a protostar
if the mass and temperature both become great enough, nuclear fusion begins in the core and a star is born

(map.gsfc.nasa.gov/ContentMedia/ M16WF2_s.jpg)

Death of a Star

Main Sequence

Size remains relatively the same for billions of years until the star begins to run out of H
H fusion begins to occur outside the core and the star begins to expand
when the H in the core is gone the He begins to fuse to produce the heavier elements C & O
 the outer lighter gases begin to blow away leaving a white dwarf (O & C core)
the gas remnants of the star absorb radiation from the exposed core creating a planetary nebula


animation of abstracted PN(heritage.stsci.edu/2000/12/ ngc6751/movie175_v1.gif)


Death of a Massive Star
Giants and Supergiants
the first steps are similar to the formation of the neutron star
fusion continues past the formation of O & C as heavier elements are created in the core (Fe)
the Fe continues to absorb the heat energy until it collapses into itself creating a massive outward shockwave
the shockwave blows the outer layers violently away from the core
supernova - explosion is 10 - 100 times brighter than our sun
neutron star
electrons are drawn into the nucleus where they fuse with protons
trillions of times more dense than our sun
affect gravity of all around them
Black hole
densest objects in the universe
gravity is so strong that light cannot escape
are seen as large emitters of X-ray radiation as atoms are ripped apart by the force of the black hole
it is now thought that most galaxies have super massive black holes at their center


Supernova Radio Map

(www.mrao.cam.ac.uk/telescopes/ supernova.gif)









(www.npaci.edu/features/ 02/02/neutron.jpg)

(zebu.uoregon.edu/~js/ast123/ images/agn.gif)

(www.space.com/images/ h_black_hole_000717_03.jpg)

(nssdc.gsfc.nasa.gov/image/ astro/hst_blkhole.jpg)









Last modified: May 30, 2003