A SUPER SYSTEM

Taranaki Daily News, 17 October 1934, Page 12

A SUPER SYSTEM

THE RIDDLE OF. GALAXIES WHAT the future may hold. are clusters disappearing? Recently reference was made in the Manchester Guardian to the remarkable extension in our knowledge of what ues beyond our galaxy. Twenty Years' ago astronomers were uncertain whether our galaxy was the only galaxy or merely one among others. , The question hinged on the‘Status; of the so-called spiral nebulae. Were they true nebulae, component parts or dependants of the galaxy, or were they systems of stars, external, situated at vast, almost inconceivable distances? The great 100-inch reflector at Mount Wilson, in the skilful hands of Dr. Hubble, settled the question once and for all about ten years ago. We now know that the so-called spiral nebulae are not nebulae but galaxies, and this is the name by which they are now coming to be known. , , Within the last ten years much has been learned concerning these external galaxies, their distances from our galaxy and from one another, and their distribution in space. Dr. Hubble, from a survey of 44,000 of these systems,- recently. concluded that they are distributed throughout space more or les3 at random, Dr. Shapley, of Harvard, however, has arrived at a different conclusion, and in a recent bulletin from Harvard College Observatory he announces that the distribution of the galaxies is markedly irregular and that there is evidence of clustering' in the region of the sky which he calls the northern galactic hemisphere. This conclusion is definitely confirmed- by •an independent investigation by Mr. Bart J. Bok, a Dutch astronomer employed at Harvard, who concludes, after a careful study of the distribution of a large number of galaxies, that “different lines of evidence all indicate that the available material points to the existence of a widespread non-uni-formity in the distribution of external galaxies, and that this tendency towards clustering is probably one of the rhlef characteristics of the part of the universe within the reach of modern telescopes.”

CENTRE OF THE UNIVERSE. What does all this mean? It means that even as the stars are irregularly distributed within our stellar system or galaxy, so the galaxies are themselves irregularly distributed within the universe. The sun is one of about 30,000,000,000 stars composing our galaxy. Within the galaxy there is a well-marked region of condensation —the star-clouds of Sagittarius, where the stars are much more numerous than in other parts ■ of Ihe system. This region of high stellar density is apparently the dynamical centre of the galaxy. If Dr. Shapley and Mr. Bok are correct in their recent conclusions the same law of distribution holds good in the system of the galaxies, * of which our galaxy is merely one component; and the region of higher density which these recent investigations have revealed may well be a dynamical centre of the super-system round which the millions of galaxies, including our own, possibly revolve. This concept of a super-system whose members are separated from one another by millions of lightyears is a staggering one; the universe, as recent astronomical progress reveals it to • vs, is vast beyond our imagining. A recent investigation by Mr. Bok on the clusters within our own glaxy has just been issued as Harvard circular 384. It is common knowledge that the stars in our galaxy are very unequally distributed. Apart from the great condensation in Sagittarius, which serves as a dynamical centre, there aro many local clusters. Some of these, such as the Pleiades, the Perseus cluster, and the Cygnus star-cloud, are familiar to the most casual star-gazer. About sixteen years ago Dr. Shapley surprised the scientic world by his announcement that the sun and the nearby stars, out to about 2000 light-years, belong to a “local cluster” which includes smaller clusters such as the Pleiades. And Dr. Shapley threw out the suggestion that the galaxy as we know it has been built up by the process of accretion—a process which, he suggested, is still going on, inasmuch as the globular clusters are rapidly approaching us, and will probably become “moving clusters” inside the main galactic system. CLUSTERS BREAKING UP. All the clusters within .our, stellar system, or galaxy, are being gradually broken up in consequence of the pull of the system as a whole. They are being dissolved, just as the sun and planets bring about the disintegration of comets and meteor streams. Mr. Bok shows, however, that these clusters are in no immediate danger. He calculates that the stars of the Pleiades will not be dispersed for 30,000,000,000 years; while the familiar configuration of the Plough will not be blotted out until at least 2,000,000,000 years have elapsed. If by any chance human life survives on the earth for so long a period, the aspect of the heavens will be much altered; our posterity will gaze on a very different sky. The clusters referred to are comparatively small ones within our local cluster: Mr. Bok baa not been able to calculate how long this cluster will endure as such. The ultimate fate of all the subordinate clusters within the galaxy would seem to be dissolution—and dissolution within what is, cosmically speaking, a comparatively short time. If the unit of star, life is, as recent cosmogonic research suggests, a billion years, and ten to twelve billion years is the average stellar “expectation of life," it is obvious that great changes will take place in the stellar system within the lifetime of the stars. The dissolution of the clusters will lead to a more or less uniform distribution' of the individual stats. More and more the lesser loyal- . ties, as it were, will be undermined, and the individual stars will be simply members of the great galaxy, moving, presumably, round the stellar centre.