Its light gradually flickered and fell, however,
and the star sank back into insignificance. But the photographic
plate now revealed a new and most instructive feature. Before the
end of the year there was a nebula, of enormous extent, spreading
out on both sides from the centre of the eruption. It was
suggested at the time that the bursting of a star may merely have
lit up a previously dark nebula, but the spectroscope does not
support this. A dim star had dissolved, wholly or partially, into
a nebula, as a result of some mighty cataclysm. What the nature
of the catastrophe was we will inquire presently.
These are a few of the actual connections that we find between
stars and nebulae. Probably, however, the consideration that
weighs most with the astronomer is that the condensation of such
a loose, far-stretched expanse of matter affords an admirable
explanation of the enormous heat of the stars. Until recently
there was no other conceivable source that would supply the sun's
tremendous outpour of energy for tens of millions of years except
the compression of its substance. It is true that the discovery
of radio-activity has disclosed a new source of energy within the
atoms themselves, and there are scientific men, like Professor
Arrhenius, who attach great importance to this source.
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