On one point the new
planetesimal theory differs from the other theories. It supposes
that, since the particles of the whirling nebula are all
travelling in the same general direction, they overtake each
other with less violent impact than the other theories suppose,
and therefore the condensation of the material into planets would
not give rise to the terrific heat which is generally assumed. We
will consider this in the next chapter, when we deal with the
formation of the planets. As far as the central body, the sun, is
concerned, there can be no hesitation. The 500,000,000
incandescent suns in the heavens are eloquent proof of the
appalling heat that is engendered by the collisions of the
concentrating particles.
In general outline we now follow the story of a star with some
confidence. An internal explosion, a fatal rush into some dense
nebula or swarm of meteors, a collision with another star, or an
approach within a few million miles of another star, scatters, in
part or whole, the solid or liquid globe in a cloud of cosmic
dust. When the violent outrush is over, the dust is gathered
together once more into a star. At first cold and attenuated, its
temperature rises as the particles come together, and we have,
after a time, an incandescent nucleus shining through a thin veil
of gas--a nebulous star.
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