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Besides bringing closer together the results for different varieties of chemical constitution, ionization
by increasing the number of supporting particles lowers the calculated temperatures considerably. It is
sometimes thought that the exceedingly high temperature assigned to the interior of a star is a modern
sensationalism. That is not so. The early investigators, who neglected both ionization and radiation
pressure, assigned much higher temperatures than those now accepted.
Radiation Pressure and MassThe stars differ from one another in mass, that is to say, in the quantity of material gathered together
to form them; but the differences are not so large as we might have expected from the great variety in
brightness. We cannot always find out the mass of a star, but there are a fair number of stars for which
the mass has been determined by astronomical measurements. The mass of the sun is -- I will write it
on the blackboard 2000000000000000000000000000 tons I hope I have counted the 0's rightly, though I dare say you
would not mind much if there were one or two too many or too few. But Nature does mind. When she
made the stars she evidently attached great importance to getting the number of 0's right. She has an
idea that a star should contain a particular amount of material. Of course she allows what the officials at
the mint would call a remedy . She may even pass a star with one 0 too many and give us an exceptionally
large star, or with one 0 too few, giving a very small star. But these deviations are rare, and a mistake
of two 0's is almost unheard of. Usually she adheres much more closely to her pattern.
How does Nature keep count of the 0's? It seems clear that there must be something inside the star
itself which keeps check and, so to speak, makes a warning protest as soon as the right amount of
material has been gathered together. We think we know how it is done. You remember the ether waves
inside the star. These are trying to escape outwards and they exert a pressure on the matter which is
caging them in. This outward force, if it is sufficiently powerful to be worth considering in comparison
with other forces, must be taken into account in any study of the equilibrium or stability of the star. Now
in all small globes this force is quite trivial; but its importance increases with the mass of the globe, and
it is calculated that at just about the above mass it reaches equal status with the other forces governing
the equilibrium of the star. If we had never seen the stars and were simply considering as a curious
problem how big a globe of matter could possibly hold together, we could calculate that there would be
no difficulty up to about two thousand quadrillion tons; but beyond that the conditions are entirely altered
and this new force begins to take control of the situation. Here, I am afraid, strict calculation stops, and
no one has yet been able to calculate what the new force will do with the star when it does take control.
But it can scarcely be an accident that the stars are all so near to this critical mass; and so I venture
to conjecture the rest of the story. The new force does not prohibit larger mass, but it makes it risky.
It may help a moderate rotation about the axis to break up the star. Consequently larger masses will
survive only rarely; for the most part stars will be kept down to the mass at which the new force first
becomes a serious menace. The force of gravitation collects together nebulous and chaotic material; the
force of radiation pressure chops it off into suitably sized lumps.
This force of radiation pressure is better known to many people under the name 'pressure of light'. The
term 'radiation' comprises all kinds of ether-waves including light, so that the meaning is the same. It
was first shown theoretically and afterwards verified experimentally that light exerts a minute pressure
on any object on which it falls. Theoretically it would be possible to knock a man over by turning a searchlight
on him -- only the searchlight would have to be excessively intense, and the man would probably be
vaporized first. Pressure of light probably plays a great part in many celestial phenomena. One of the
earliest suggestions was that the minute particles forming the tail of a comet are driven outwards by the
pressure of sunlight, thus accounting for the fact that a comet's tail points away from the sun. But that
particular application must be considered doubtful. Inside the star the intense stream of light (or rather
X-rays) is like a wind rushing outwards and distending the star.
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By PanEris
using Melati.
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