18084TM@MSU.BITNET (Tommy Mac) (12/14/90)
Hey folks! I just jumped on this listserv (Like it a lot, too), and it looks
like I'm getting about a weeks delay in recieving things. I don't know if this
is true for the rest of you, so if it seems like I'm out in the dark on some of
these topics, that's why:
Re; Vulcan. It seems that I remember "Vulcan", as a planet name was first used
for the planet that some believed held the same orbit as Earth, but at constant
conjunction with Sol (other side). Does this sound familiar? I think they
dropped this idea quite a while ago.
Re; Black Holes
Ray, remember your four forces. Star happen because of gravity defeating
the weak force (I think), as do white dwarves and nuetron stars. Black
holes happen when gravity defeats the strong force (this is the strongest
of the four). The reason they are black is because light doesn't move faster
than their escape velocity, so no matter how 'unstable' it might become, it
could not explode, if you define exploding as matter being thrown from it. If
light doesn't move fast enough to escape, how could matter? The structure of a
black hole is totally unknown because we simply can't see it. The best images
we have of black holes are based on the assumption that they are compressed by
gravity until not even nuetrons hold up to the pressure. This kind of force
would certainly create stability, as nothing can move. Although, spinning
holes could be another story...
Re; Politicians in space.
I have no idea what the record or beleifs of "barfin" are, but; Every naut
(astro and cosmo) has returned with new impressions of earth, usually focussing
on 'oneness' with others, fragility of the biosphere, lack of natioanal borders
and other similar visions. Maybe we should send all politicians into space, or
have all the arms talks there. Maybe we'd get some long-range policy enacted
by this frustrating and petty group.
Re; space stations
When the polynesians (sp?) left on their sea voyages for the islands of the
pacific, they certainly did not plan to return, so they did not build ports.
likewise, all the people who have created successful 'deep space' missions
did not include a space stations (viking, mariner, galilieo, voyager, etc), for
what I think are obvious reasons.
The moon mission was a few shot, exploratory/show-off mission, not a trip
with long-range planning in mind. I'm quite certain that Magellan and
Columbus did not start buying property at every place they landed with the
intention of building ports (wasn't cost-effective).
However, if we want a permanent place in space, a space "station" is very
necessary. Why?
-Space in space. GEO is a very popular place (all of you watching Satcom for
NASA broadcasts know that). With space stations, the density of GEO vehicles
can be increased, allowing greater use of this position
- Storage. Currently, the ETs from the Shuttle are dropped into the Indian
ocean, at a net payload loss, because of lack of something to do with them
in space. A station would allow their storage for future use, as well as the
fuel that is left in them after a boost.
- Industrial processing. Any industrial processing in space (not glass beads
and crystals, I'm talking energy and raw materials) will require a lot of
equipment. Put it all in one place, add some docking ports and habitats, and
you've got a station. Why not send up the parts we can use now with this end
in mind? If you don't want to live or create in space, then why do you read
this stuff?
- Use of cis-lunar space. Of course, the best place for this kind of station
would be on the moon. Does that make it a 'planet-station'?
----Build a PRACTICAL (i.e. designed with long-range goals) space station, and
let the space age begin
-If God had wanted us to travel in space, he would have given us a
large moon full of metal oxides (applies to viewing the corona too)
Tommy Mac
Acknowledge-To: <18084TM@MSU>neufeld@physics.utoronto.ca (Christopher Neufeld) (12/14/90)
In article <Added.YbO0zVm00Ui3ML4E9l@andrew.cmu.edu> 18084TM@MSU.BITNET (Tommy Mac) writes: > >Re; Black Holes >Ray, remember your four forces. Star happen because of gravity defeating >the weak force (I think), as do white dwarves and nuetron stars. Black >holes happen when gravity defeats the strong force (this is the strongest >of the four). > Stars form because of gravitational collapse of gas clouds. If there is any countering force, it would be electromagnetic, radiation pressure pushing back on the infalling gas because it is heating up at the centre, even before nuclear ignition. The weak force has much too short a range to be significant in interactions between particles separated even by micrometres. A white dwarf is formed when the star collapses after nuclear burnout, and the Fermi pressure of electrons holds off the gravity. If the star is too massive, the electron Fermi pressure will never equal that of gravity. A proton+electron -> neutron+neutrino reaction converts most of the mass to neutrons, which are able to exert a higher Fermi pressure than electrons, so the collapse stops. If the star is even more massive, it may be heavy enough that neutron pressure can't stop the collapse. There's no known mechanism which can prevent the mass from falling in past its own event horizon in this case, and a black hole is formed. Note that a black hole does not have to have a mass singularity, and it doesn't have to start in the form of degenerate matter. The radius of a black hole (Schwarzschild radius) is proportional to the mass of the body, while the volume goes as the cube of the radius. If all the stars in the galaxy were placed in a sphere whose radius was that of our solar system, the stars wouldn't touch each other, but the resulting construct would be a black hole. A quick explanation of the Fermi pressure I was describing before: from basic physics or chemistry you know that no two fermions can have the same set of quantum numbers. There turns out to be a set of quantum numbers associated with the volume available for the fermions to travel. A white dwarf sets a limit to how far the electrons can travel, they can't leave its surface. The quantum numbers, proportional to momentum, and hence to the square root of kinetic energy, scale up themselves as the reciprocal of the linear dimension of the object, here it would be the radius. So, if the star is compressed, all the momenta of the electrons shift up. This means that the kinetic energy stored in the electrons is higher, so you have to have done some work on the system to get it there. This implies immediately that you compressed it against some pressure. So, a white neutron star isn't stable because some other elementary force is pushing back against gravity, but rather because it has fallen to the bottom of an energy well. Squeezing it farther would reduce the gravitational potential energy of the mass distribution, but it would raise the internal energy of the star by a greater amount, and so it is energetically unfavourable for it to squeeze farther. A more complete discussion can be found in any moderately good book on statistical mechanics, or in chapter 11 of Weinberg's _Gravitation and Cosmology_. -- Christopher Neufeld....Just a graduate student | neufeld@helios.physics.utoronto.ca Ad astra! | S = k log W cneufeld@{pnet91,pro-micol}.cts.com | Boltzmann's epitaph "Don't edit reality for the sake of simplicity" |