Stellar evolution

“ But if there is annihilation of matter the life of the sun and the loss of mass continue far longer, and an extended track of evolution lies open before the sun; when it has got rid of three-quarters of its present mass it will have become a faint star like Krueger 60.
Our choice between the possible theories of subatomic energy only affects stellar evolution in one point—but it is the vital point. Unless we choose annihilation of matter, we cut the life of a star so short that there is no time for any significant evolution at all. ”

“ Furthermore, it soon became apparent that the light of a star, as decomposed by a prism, was competent to define the star's position in a general scheme of development, in which every advance, from the unformed nebulous cloud on through the highest degree of stellar brilliancy to such a final stage as is typified by the moon, can be defined with but little danger of error. Before we proceed to consider some of the evidences of stellar evolution, let us examine some of the instruments and methods without which the discoveries to be subsequently described would have been impossible. ”

“ So immensely distant are even the nearest of these multitudinous bodies that no telescope can ever be built large enough or powerful enough to reveal a dark planet as large as Jupiter, alongside even the nearest fixed star. Whatever may be the process of stellar evolution, there doubtless is an era of many hundreds of millions of years in the life of a star when it is passing through a planet-maintaining stage. ”

“ With such a motion, not only would the risk to our solar system be removed, but the collisions between the dark bodies themselves would be a matter of rare occurrence; and hence the energy of the universe would be conserved. And when a collision did happen it would be on a grand scale, and the result would be not an imperfect sun without planets, but an incandescent nebula, out of which, by condensation, a complete solar system would be evolved. ”

“ If the former, then, according to the theory that stellar heat had its origin in collision, it is presumptive evidence that space is occupied by dark bodies far more numerous and massive than the luminous ones which the telescope reveals. ”

“ The impact theory does not rest upon a purely hypothetical basis. The cause to which it appeals has a real existence. The point of uncertainty is whether the cause actually produces the effect which is attributed to it. We know from observation that there are stellar masses, some of them probably larger than our sun, moving through space with enormous velocities in all directions. ”

“ If an individual star is to progress any part of the way down the main series it must lose mass. We can put the same inference in a more general way. Now that it has been found that luminosity depends mainly on mass, there can be no important evolution of faint stars from bright stars unless the stars lose a considerable part of their mass.
It is this result which has caused the hypothesis of annihilation of matter to be seriously discussed. All progress in the theory of stellar evolution is held up pending a decision on this hypothesis. ”

“ There can be little if any doubt that our own sun once passed through the successive stages which are represented by the spectra shown in Fig. 8. The time which has elapsed since it acquired its present size and density as the result of the condensation of the great nebula in which the earth and the other planets also had their origin, covers many millions of years. It is fortunate for the study of stellar evolution that the stages through which the sun once passed are all exemplified in existing stars, which for unknown reasons began their stellar life at widely different times. ”

“ From what has been stated it would follow that in most cases the stellar masses have been formed out of the destruction of pre-existing masses, like the geological formations out of the destruction of prior formations. ”

“ The probability is that all the chemical elements composing it would be in a state of utter dissociation, and converted back into the original protyle from which they were derived, again to be slowly reconverted into their former atomic condition as the temperature fell.
Can we on scientific grounds trace back the evolution of the universe to an absolute first condition?—As has been repeatedly stated, all inquiries into the evolutionary history of the stellar universe begin in the middle of a process. Evolution is a process. ”

“ STELLAR EVOLUTION This actual measure of the diameter of Betelgeuse supplies a new and striking test of Russell's and Hertzsprung's theory of dwarf and giant stars. Just before the war Russell showed that our old methods of classifying the stars according to their spectra must be radically changed. Stars in an early stage of their life history may be regarded as diffuse gaseous masses, enormously larger than our sun, and at a much lower temperature. Their density must be very low, and their state that of a perfect gas. ”

“ It will be only when the two bodies, coming from contrary directions, collide with equal momentum that the entire motion will be stopped. But in the case of stellar masses moving, as it were, at random in every direction this is a condition which will but rarely occur. Accordingly, in most cases the resulting stars will have more or less motion. In short, the stars should, according to the theory, be moving in all directions and with all varieties of velocity. ”

“ So far had the detailed chemistry of the stars been carried in the latter years of the century that the question of stellar evolution gave rise to that of inorganic evolution generally, the sequence in the phenomena of which can only be studied in the stars, for laboratory work without stint has shown that in them we have celestial furnaces, the heat of which transcends that of our most powerful electric sparks. In this way astronomy is paying the debt she owes to chemistry. ”

“ For evidences of decay we must investigate the red stars, in which the radiation of heat throughout immense periods of time has resulted in cooling toward the point of final extinction. Thus we may untangle the great problem of stellar evolution, and at the same time build up a complete history of the sun, learning what it has been, what it is and what it will become. ”

“ The theory starts with the assumption that the greater part of the energy possessed by the universe exists or is stored up in the form of the motion of stellar masses. The amount of energy which may thus be stored up is startling to contemplate. Thus a mass equal to that of the sun, moving with a velocity of 476 miles per second, would possess, in virtue of that motion, energy sufficient, if converted into heat, to maintain the present rate of the sun’s radiation for 50,000,000 years. ”

“ In seeking for evidence of stellar evolution, on a plan comprehensive enough to include a place for every star in the heavens. we may begin with visual and photographic observations with the telescope. Such remarkable photographs as that of the Andromeda nebula seem to bring us into the very presence of a greater system, more nearly comparable in size with the Milky Way than with the solar system, in the actual process of formation. ”

“ It thus appears that if the powerful instruments required for these investigations can be provided, the opportunity should exist during the next quarter of a century to make important additions to our knowledge of the origin and development of the sun, and at the same time to throw new light on the great problem of stellar evolution. ”

“ As the sudden compression of a portion of atmospheric air yields heat sufficient to ignite tinder, or fuse and volatilise a descending meteor-mass, so the precipitation of one planet upon another would liberate sufficient heat to reduce them both to a state of fusion, or even of vapour. Still more must the intensest heat be generated by the impact of two nebulous masses, one or both of which together may embrace more matter than all our planets and the sun combined—as much even as the matter of our entire visible firmament of stars. ”

“ Much light has been thrown on it by recent investigations, rendered possible by the development of new and powerful instruments and by advances in physics of the most fundamental character. All the evidence confirms the existence of dwarf and giant stars, but much work must be done before the entire course of stellar evolution can be explained. ”

“ If the latter, viz. that the star has a velocity which never could have been produced by attraction, “then,” as says Professor Newcomb, “it must have been flying forward through space from the beginning, and, having come from an infinite distance, must now be passing through our system for the first and only time.” The probability is, however, that the star derived its motion from the source from which it derived its light and heat; namely, from the collision of the two masses out of which it arose. If the star is ever to be arrested in its onward course, it must be by collision ”

“ If the collisions were insufficient in character, the fewer of them that occurred, the better; for the result of such collisions would simply be a waste of the potential energies of the universe. We should in this case have an innumerable host of imperfect suns without planets, or with at most only one or two, and these at no great distance from the luminary. There would thus be evolved a universe without any grand planetary systems. ”

“ A comet, for example, having an orbit extending to the path of the planet Neptune, approaching so near the sun as to almost graze his surface in passing, would have a velocity within 86 miles of what we have assumed. Twice this assumed velocity would give 200,000,000 years’ heat; four times the velocity would give 800,000,000 years’ heat; and so on.
We are at perfect liberty to begin by assuming the existence of stellar masses in motion; for we are not called upon to explain how the masses obtained their motion, any more than we have to explain how they came to have their existence. ”

“ If the solar nebula thus produced would be swelled out into a spherical incandescent mass with a radius 40 times the radius of the earth’s orbit, simply because the globes fell from a distance of 100 times the radius of that orbit, then for a similar reason the mass would have a radius of 400 times that of the earth’s orbit had the globes fallen from a distance of 1,000 times the radius, and 400,000 times if the globes had fallen from a distance of 1,000,000 times the radius, and two-fifths of any conceivable distance from which they may have fallen. ”

“ A star cluster will result from an immensely widespread nebula breaking up into a host of separate nuclei, each of which becomes a star. The irregular manner in which the materials would, in many cases, be widely distributed through space after collision would prevent a nebula from condensing into a single mass. Subordinate centres of attraction would be established, as was long ago shown by Sir William Herschel in his famous memoir on the formation of stars ”

“ According to the ordinary laws of chance, collision at times would be an inevitable result, and when such an event did take place the destruction of the colliding bodies, and their consequent transformation into a nebulous mass, would, at least in many cases, be a necessary result. In fact, we have, in the case of these vast stellar masses, what we know occurs among the invisible molecules of a gas. So far as mere analogy is concerned, the impact theory is just about as probable as the other. ”

“ There is strong presumptive evidence that the motion of the stars is due to this cause. We know that there are stars which have a far greater velocity than can result from gravitation, such, for example, as the star 1830 Groombridge, which has a velocity of 200 miles per second. Suppose, with Professor Newcomb, that the number of stars belonging to the universe amounts to 100,000,000, and that these have, on the average, five times the mass of the sun, and are spread out in a layer across which light requires 30,000 years to pass. ”

“ For more than a century past the problem of the evolution of the stars, including the solar system and the Earth, has occupied the central place in astronomical thought. No one is bold enough to say that the problem has been solved. The chief difficulty proceeds from the fact that we have only one Earth, one solar system and one stellar system available for tests of the hypotheses proposed ”

“ The result in this case would, no doubt, be that the untransformed fragments, drawn together by their mutual attractions, would collide and form an imperfect star or sun, without a planet. Such a star might continue luminous for a few thousands or perhaps a few millions of years, as the case might be, when it would begin to fade, and finally disappear. We have here an imperfect nebula, resulting in an imperfect star. In short, we should have in those stellar masses, on a grand scale, what we witness every day around us in organic nature, viz. ”

“ It has now attained the zenith of its evolution, and is breaking up into molecules, or solar systems, which again are composed of stellar bodies, or atoms within the molecule. In violent exuberance of youth these rush through space in fulfilment of their individual life. Many will in due time undoubtedly become dust again and then serve to nourish a new youthful nebula. Others succumb to a freezing-death but will be restored to life in collision with a nebulosity or some other stellar body and give form to “new stars” or planetary clouds. ”