I'm a little rusty on my astronomy hobby, but here goes.
> 1) what classifies a star type (eg. sol is a G-type star, what's that mean?)
> Also, what are the other classes of stars and what does that mean for
> the star system (I think it has something to do with star burn rates).
Stars are classified by many things. The most important factors in
stars are mass, composition, and distance from the observer. From these
everything else can be deduced:
Basic Stellar Factors:
Mass: Stars vary from 1/100 to 100 times the Sun's mass. At
certain cataclysmic times in their lives, stars will lose mass
(from 10% to 99% of their starting mass). Sometimes stars will
scoop up mass from the atmosphere of a nearby companion. Most
stars are about 10-20% of the sun's mass. Stars larger than the
sun get progressively rarer, mostly due to their short lifetimes.
Composition: Stars start out with about 75% Hydrogen and 25%
Helium. Stars formed from the ashes of earlier stars which have
Nova'ed may have dust formed from elements Iron and lighter.
Stars formed from the ashes of Supernovae (like most stars in
our galaxy today) are further enriched with elements heaver than
Iron. Composition is the single most important factor which
causes stars to age. As stars age they fuse the Hydrogen nuclei
into Helium nuclei. Stars somewhat more massive (>1.4 Solar
masses) can develop the core pressure to burn the Helium into
Carbon, Carbon into Neon, Magnesium, and so on up to Iron. The
smaller stars (<1.4 Solar masses) run out of fuel, blow off
their outer layers, and cool into a naked degenerate matter core
called a white dwarf. The larger stars run out of fuel, blow
off their outer layers in a supernova, and press all the
electrons and nuclei together (in the naked core) called a
neutron star. Or maybe a black hole.
Distance from observer: affect the apparent brightness of the
star. Naturally it has no effect on the intrinsic brightness of
the star.
Resultant factors:
Core Temperature: A function of mass and composition. A few
million degrees Kelvin is necessary to fuse Hydrogen. Several
hundreds of millions of degrees are necessary to create Iron.
Temperature (and Pressure) of that magnitude can only be
achieved in the most massive stars. The core temperature and
pressure is increased by gravitional collapse, and decreased by
the radiation pressure of the gamma rays generated by fusing
elements. As the fusion rates increase, the core expands,
reducing the temperature and pressure, causing the fusion rate
to decrease. This steady state is why stars burn at a steady
rate. Very massive stars have stronger gravity-pressure to
overcome, so they reactions stabilize at vastly higher reaction
rates.
Size: The girth of the star is determined most importantly by
its composition and core temperature. Most normal composition,
that is, main sequence stars (type V) are compact, that is,
about 1-10 million km in size. Stars made of white-dwarf matter
are subcompact (Earth size), and neutron stars are microcompact
-- only a few km (say 15 or so) across. Red giants, where the
core temperature is very high and is goading fusion reactions on
the star's surface, are bloated out to 100 million to 1 billion
km in size.
Surface Temperature: A function of mass and size. Most surface
temperatures are in the 3000K-45000K range. Sol burns at about
5600K. Redder "colors" are cool, 3000-4000K. Yellow is
5000-7000K, White is 8000-15000K, and the hotter stars have a
distinctly bluish tint. This is because the photosphere
(deepest visible layer of the star) radiates like a black body,
in a continuous bell-curve of luminosity vs. wavelength. White
dwarfs tend to be whitish, Red Giants bloated by high core
temperatures and high-atmosphere hydrogen burning are very cool
on the surface.
Luminosity: The intrinsic brightness of the star; it's total
energy output. This is a function of the star's size and its
surface temperature. White dwarfs are hot and very small, so
they are dim. Neutron stars are hotter still and tinier still,
so they are even dimmer. Red Giants are cool but very large, so
they tend to be very bright. Stars range from 10000 to
1/10000'th the luminosity of Sol.
Observable information:
Apparent magnitude: How bright the star looks from your
backyard. A combination of luminosity degraded by distance.
This is a logarithm of the apparent brilliance of the star. Sol
is magnitude -26 or so, the Moon, about -16, Sirius A (brightest
star) is -1.6, Alpha Centauri A, about 1.0, dimmest observable
with unaided human eye, about 6.0, Sirius B (white dwarf), about
15.0.
Absolute magnitude: Magnitude of star if it were brought to a
fixed distance of 10 parsecs. I think the Sun would be around
magnitude 4.0.
Color Index: The degree of blueness or redness of the star as
measured by comparing the brightness of the star from two
photographs, one taken through blue and the other through a red
filter.
Spectrum: A spectrograph is used to look at the emission of the
star at each visible wavelength. The bell curve of black-body
radiation is most evident (hotter stars are bluer, colder are
redder). On closer examination, dark and bright lines can be
distinguished. The dark lines are caused by gases in the star's
atmosphere absorbing light from the lower layers; the bright
lines are emissive gases in the star's atmosphere. The exact
position of the lines map out the composition of the stars to
observing scientists. Hot stars tend to have very understated
emission/absorption lines, whereas the cooler stars have very
pronounced absorption lines.
The spectral class of the star attempted to classify the stars
from the spectral lines, and originally we had type A through
type S stars, with type W Wolf-Rayet stars too. After much
studying and theorizing, they realized everything was screwed
up. They threw out most of the letters as meaningless, and came
up with the order O B A F G K M, which classifies normal (type
V) stars in order of decreasing temperature and size. For finer
degrees of measurement, a decimal was added. Hence Sol is 2/10
of the way from G0 to K0, a G2 star.
Stellar lifecycles:
Formation: all stars form from clouds of dust and gas. Areas of
the clouds will be more dense, and the stronger gravity there
draws in surrounding gas, etc., until a proto-star system is
born. Often the central mass will have other similarly sized
clumps gathered with it. This is a multi-star system. Others
may not, like the Sol system. Any tiny planets tend to clump
together as the star is warming up. Eventually the star heats
up really good and blows away most of the dust and gas around
it. Often the young star burns off the volatiles from the
close-in planets, while the outer ones maintain their hydrogen
and helium envelopes (gas giants).
Main Sequence Life: About this time it probably emerges from the
cluster (in the case of galactic clusters) or spiral arm and
enters the long-term hydrogen-burning steady state "main
sequence". The star spends most of its life converting hydrogen
into helium, at modest core temperatures. This is the time a
star is considered "type V". For Sol, this is around 10 billion
years. For more massive stars, much less time (higher core
temperatures and much greater burning). Sirius A, a class A
star, probably will last 200 million years or so. For less
massive stars (class M), 40-50 billion years.
Uh-oh, low on gas: When the star runs low on hydrogen, the core
will no longer be able to support itself against gravity, and
will shrink, compressing and heating up. The hydrogen outside
the core, what ther is, starts burning like crazy. The intense
heat of this causes the star to bloat hugely into a red giant.
Small Stars: In small stars (1.4 Solar masses or less), the core
will tend to continue collapsing into a state of degenerate
matter called a white dwarf. The remnant core will then blow
off the outer layers of the star into a "plentary nebula". The
inert dwarf, just hot matter with no energy generation, will
slowly cool over billions of years, going from spectral class B
or so down to M and below (a black dwarf).
Large Stars: The core will collapse futher and further until it
gets hot enough to fuse the plentiful helium ash into carbon.
The star has a new lease on life, but the intense temperatures
makes the helium burn very quickly and it lasts only 1/10 to
1/100 as long as the hydrogen lasted. When it runs out, the
story is repeated. THe core collapses until it is hot enough
for carbon to fuse. The star is like an onion, with hydrogen
burning on the surface, helium below, carbon below that. This
can't go on forever. When the star reaches Iron, it cannot fuse
any more to gain energy.
Neutron Star: at this point the core continues collapsing until
the electrons, protons, and neutrons are crushed into a gigantic
ball of neutrons 10-30 km across, the rest of the star falling
in around it. Suddenly the core stops collapsing, and the
infalling matter crashes against the core, rebounding with a
gigantic shock wave which is crushed out before it can leave the
star. At this point heavy elements are created by crushing the
iron and lighter nuclei together. A massive burst of neutrinos
is the neutron core's shockwave of its own. The neutrinos,
unlike photons, mostly pass through the matter of the star, but
those that do collide into the star's matter heat it violently
and the star's outer 95% rends itself away from the core. This
is called a Supernova. The remnant is a neutron star. If the
star was very massive, the neutron star will collapse at this
point into a black hole.
The Remnant: The supernova remnant is highly enriched in heavy
elements. Undoubtedly the gases and dusts will be swept into
more star formation in a few million or billion years. Think of
the gold in the switches in your computer terminal. Yep, those
came out of a supernova long before the solar system formed.
> 2) Are there any physics/astronomy/astrophysics people out there who
> could tell us what a *real* binary/trinary star system would look
> like ('yes' and 'no' are *not* appropriate answers :-).
I suggest going to a star party and asking to see a couple
binaries/trinaries. There are many paintings by artists depicting life
on a planet ruled by binary/trinary star systems. Read "Nightfall"
(don't see the movie) by Larry Niven and ???.. Look for art in
"Cosmos", by Carl Sagan.
> 3) Ar there any other star system types that are known to exist aside
> from the stardard unary/binary/trinary systems? (Ringworld and Dyson
> sphere systems are man/being-made and can be anything we want them
> to be).
Other than multi-star systems and globular and galactic clusters, there
aren't really any other kinds of systems. Globular clusters are
ancient, one-shot star formations of several million stars, very poor in
heavy elements. Galactic clusters (and galactic arms) are full of dust,
gas, and radiation. They are full of young, hot, massive stars that go
"pop" and raise a lot of radiation.
> 4) what does "Planet's rotation is in a resonant spin lock with the star"
> mean?
Mercury is an example. It is in an eccentric orbit, and contains uneven
distribution of mass within itself. It revolves around the Sun in 88
days, and rotates in 59 days. Note the 3:2 ratio, a ratio of small
integers. This has happened because of a resonance; when Mercury is
closest to the Sun, the lowest energy state is when the mass
concentrations on Mercury closest to the Sun. The Moon is a similar
case in it's orbit around earth, only the ratio is 1:1. This effect is
usally felt only when the objects are fairly close to one another, and
have been orbiting for a long, long time.
CraftID: Child's Tricycle, TL 15, kCr265 | James T. Perkins 568BB8, 23 years
Hull: Config=1AF, Armor=10G | Traveller Mailing List Adminstrator
Power: Fusion=1MW, Duration=45/135 | Homeworld: Earth D867A74-8
Loco: StdGravThrust=1ton, NOE=190kph | Computer-2, Physics-1, Leader-0,
Off/Def: Pintel:VRFGauss,1600rounds/min | Wheeled Vehicle-1, Mechanical-1,
Accom: Operator=1, Seats=crampedx1 | Electronics-1, History-0