Lord Rosse’s nebula
But since Keeler’s discovery there has been a decided turning away of speculation another way. The form of the spiral nebulæ seems to be entirely inconsistent with the theory of an originally globular or disk-shaped nebula condensing around a sun and throwing or leaving off rings, to be subsequently shaped into planets. Some astronomers, indeed, now reject Laplace’s hypothesis in toto, preferring to think that even our solar system originated from a spiral nebula. Since the spiral type prevails among the existing nebulæ, we must make any mechanical theory of the development of stars and planetary systems from them accord with the requirements which that form imposes. A glance at the extraordinary variations upon the spiral which Professor Keeler’s photographs reveal is sufficient to convince one of the difficulty of the task of basing a general theory upon them. In truth, it is much easier to criticize Laplace’s hypothesis than to invent a satisfactory substitute for it. If the spiral nebulæ seem to oppose it there are other nebulæ which appear to support it, and it may be that no one fixed theory can account for all the forms of stellar evolution in the universe. Our particular planetary system may have originated very much as the great French mathematician supposed, while others have undergone, or are now undergoing, a different process of development. There is always a too strong tendency to regard an important new discovery and the theories and speculations based upon it as revolutionizing knowledge, and displacing or overthrowing everything that went before. Upon the plea that “Laplace only made a guess” more recent guesses have been driven to extremes and treated by injudicious exponents as “the solid facts at last.”
Wonderful spiral in triangulum
Before considering more recent theories than Laplace’s, let us see what the nature of the photographic revelations is. The vast celestial maelstrom discovered by Lord Rosse in the “Hunting Dogs” may be taken as the leading type of the spiral nebulæ, although there are less conspicuous objects of the kind which, perhaps, better illustrate some of their peculiarities. Lord Rosse’s nebula appears far more wonderful in the photographs than in his drawings made with the aid of his giant reflecting telescope at Parsonstown, for the photographic plate records details that no telescope is capable of showing. Suppose we look at the photograph of this object as any person of common sense would look at any great and strange natural phenomenon. What is the first thing that strikes the mind? It is certainly the appearance of violent whirling motion. One would say that the whole glowing mass had been spun about with tremendous velocity, or that it had been set rotating so rapidly that it had become the victim of “centrifugal force,” one huge fragment having broken loose and started to gyrate off into space. Closer inspection shows that in addition to the principal focus there are various smaller condensations scattered through the mass. These are conspicuous in the spirals. Some of them are stellar points, and but for the significance of their location we might suppose them to be stars which happen to lie in a line between us and the nebula. But when we observe how many of them follow most faithfully the curves of the spirals we cannot but conclude that they form an essential part of the phenomenon; it is not possible to believe that their presence in such situations is merely fortuitous. One of the outer spirals has at least a dozen of these star-like points strung upon it; some of them sharp, small, and distinct, others more blurred and nebulous, suggesting different stages of condensation. Even the part which seems to have been flung loose from the main mass has, in addition to its central condensation, at least one stellar point gleaming in the half-vanished spire attached to it. Some of the more distant stars scattered around the “whirlpool” look as if they too had been shot out of the mighty vortex, afterward condensing into unmistakable solar bodies. There are at least two curved rows of minute stars a little beyond the periphery of the luminous whirl which clearly follow lines concentric with those of the nebulous spirals. Such facts are simply dumbfounding for anyone who will bestow sufficient thought upon them, for these are suns, though they may be small ones; and what a birth is that for a sun!
Look now again at the glowing spirals. We observe that hardly have they left the central mass before they begin to coagulate. In some places they have a “ropy” aspect; or they are like peascods filled with growing seeds, which eventually will become stars. The great focus itself shows a similar tendency, especially around its circumference. The sense that it imparts of a tremendous shattering force at work is overwhelming. There is probably more matter in that whirling and bursting nebula than would suffice to make a hundred solar systems! It must be confessed at once that there is no confirmation of the Laplacean hypothesis here; but what hypothesis will fit the facts? There is one which it has been claimed does so, but we shall come to that later. In the meanwhile, as a preparation, fix in the memory the appearance of that second spiral mass spinning beside its master which seems to have spurned it away.