rk2001's write up is mostly wong. Until this coming
thursday I will be a professional
astrophysicist,
well a graduate student at any rate, after that I move
into interactive cinema, but that's another story,
here then is my expert commentary.
Protostar
The first scentence is fairly accurate, gravitational
instability causes clouds to collapse. The centre of the
cloud heats up and becomes dense,
fusion occurs.
The opacity of the star is so high that the radiation
becomes thermalised, i.e. the radiation spectrum
is a
Black Body spectrum and hence the star emits
at all wavelengths.
I pity the poor fool that
lives by a star which emits
gamma rays alone,
I especially worry about their sunblock bills.
Red Giant
Red Giant is a stage in the life cycle of some stars,
it is not the radiation nor the energy released during the formation of a star. It is one of the last stages in
the evoloution of a star. Once most of the fuel of a star
has been spent (after say 10 billion years for the average
G star) the internal dynamics of the star becomes
somewhat unstable. This causes the outer layers to balloon
out, whence the monicer Giant is derived. As the surface area of the outer layer increases so dramatically
the temperature drops according to conservation of energy and the star becomes signifigantly redder than before.
White Dwarf
Any star that will eventually form a white dwarf
will not only burn all of it's hydrogen into helium
but also all of it's helium in to calcium,
and so until all that is left is an iron core.
The final Hydrogen burning will be completed before
the star reaches the Red Giant stage, the white
dwarf stage is after the ref giant stage. The unstable nature of the interior of said star will cause the
outer layers to be ejected forming what is known
as a planetary nebula, M51, the ring nebula
visable just off of the constalation Cygnus
is a wonderful example. When the outer layers are cast aside
the still glowing core is a small compact
(one might even say dwarf like)
and hence bright (or white) object. There is no longer
any burning and the white dwarf will slowly
cool. Some white dwarf's do not make it through to
Iorn and are just carbon, they eventually crystalise,
think of that, giant diamonds in the sky.
Black Dwarf
No astronomical object has this name.
Neutron Star
If a star is big enough it will turn into
a supernova. The star can be thought of as
a tug of war between gravity attempting to
collapse the star and the burning which provides a pressure
against collapse. When the core has burnt through to Iorn, no more energy can be realesd through fusion and the
pressure against gravity stops. Gravity wins and
squeezes the core of the star. The electons in the iorn
core are forced in towards the neuclei as the desnity rises.
The electrons combine with the positorns and the only material left are neutrons closly packed together.
Nuclear degenercy pressure provides support against the collapse. The outer layers get blown away from
the recoil against the now neutron core. The remnant is
a neutron star, left over after the explosion.
Supernova
A star that has exploded, the brightest stage of a star's life.
Pulsar
If a star becomes a pulsar it is likley that it will never
become a black hole. A pulsar is a neutron star
with an accretion disk. As the matter falls onto
the pulsar it gets ejected along the axis of rotation of the star. We don't understand well why this happens, but it
is ubiqitous amonst systems with accretion flow.
The radiation out along the poles is continious
but as the star precesses the direction of this cone
gets swept around in a circle. If we are in the path
of this beam we see pulsed radiation, the pulsar
acts like a cosmic lighthouse.