Honors 1500 - It= s About Time
The Spectral Sequence
high mass, bright, hot, short MS lifetimes <B O B A F G K M B > low mass, dim, cool, long MS lifetime
(MS = main sequence on the Hertzsprung-Russell diagram)
Summary of Stellar Evolution
all stars
interstellar cloud of gas (mostly hydrogen and helium), ices, and dust
cloud undergoes gravitational collapse to form a protostar
protostar=s center becomes hot enough for nuclear fusion reactions
fusion of hydrogen nuclei (protons) B > helium nuclei begins in the protostar=s core
newborn star on the main sequence of the Hertzsprung-Russell diagram
time passes: 10 billion years for a low-mass G star (our Sun)
15 million years for a high-mass B star
all hydrogen available for fusion in center converted into helium
star's core contracts and heats, surface expands to become a red giant
fusion of helium nuclei B > carbon and oxygen nuclei begins
all helium available for fusion in center converted into carbon and oxygen
star becomes a red supergiant
| low-mass star |
intermediate-mass star |
high-mass star |
| inert carbon-oxygen core |
more fusion produces inert
iron core |
more fusion produces inert
iron core |
| outer layers of red
supergiant ejected to form a planetary nebula |
core of red supergiant
collapses to form a supernova |
core of red supergiant
collapses to form a supernova |
| carbon-oxygen core remains as
a white dwarf |
neutron core remains as a
neutron star |
neutron core collapses to
form a black hole |
| white dwarf cools and crystalizes | neutron star cools |
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Last modified: Sunday, April 24, 2005 04:16 PM
low-mass
inert carbon-oxygen more fusion produces more fusion produces
core inert iron core inert iron core
outer layers of core of core of
red supergiant red supergiant red supergiant
ejected to produce collapses to produce collapses to produce
a planetary nebula a supernova a supernova
carbon-oxygen core neutron core neutron core
remains as a remains as a collapses to form a
white dwarf neutron star black hole
white dwarf cools neutron star cools
and crystalizes