THE LIFE OF A STAR.

Auckland Star, Volume LV, Issue 169, 18 July 1924, Page 7

THE LIFE OF A STAR.

A GRAND UNIFORMITY. £ THROUGHOUT NATURE. DISCOVERIES REVIEWED. Profeseor H. H. Turner reviews certain of the recent sensational discoveries that 4 j have been announced at the Royal t I Astronomical Society. He shows how a - very remarkable uniformity has been introduced into modern views on the his- 2 tory and development of the stars. In j the article, which appears in the "Morn- a ing Post," Professor Turner states:— "Einstein's theory, now fully established, seenis to leave us with nothing but relative motion—nothing denoting 'rest' in , our universe, and yet the calcium clouds , to which Mr. Evershed first drew attention in 1919 seem to supply just that standard which Einstein declares impos- . sible. There are, of course, ways of J reconciling the two Ideas, but it is more I amusing to leave them facing one another : in apparent contradiction. ' "Scarcely had we time to acquire a ' new appetite for the sensational when . Professor Eddington (of Cambridge) gave J us a splendid feast. On March 14 he put forth a revolutionary view of the 1 life history of a star—the views which ! he overturned being those of no one more conspicuously than of himself. It was his own brilliant mathematical work ' on the evolution of a star which held the field, though it was regarded as con- * firming the views previously expounded ' by Professor H. N. Russell (of Prince- < ton, U.S.), which he had developed from ' observations of the brightness, distances < and special type of stars. Knowing the £ apparent brightness of a star and its ' distance, we can calculate its real or 1 standard brightness, i.e., that which it v would have at a selected standard dis- 1 tance. The stars can then be arranged 1 in sequence according to this standard < brightness or 'luminosity,' and it is then i found that the spectral type (which 1 represents the physical state of the surface) also ranges itself in the same c sequence, which, as we have come to ( believe, represents the life history of a ( star. " i The Turning Point. « "But there is one important proviso, viz., the same spectral type occurs twice over in the' history, once in the order, £ M, X, F, A,' B (to use the technical letters, the meaning of which, however, need not concern us), and then back- ' wards in the order B, A, F, X, M. Type ' M denotes both an early and a late etage ' in the sequence, just aa absence of teeth and hair may characterise either a baby j |or an old man. In between these ex- ' I trcmes there is a turning point, and 'before Professor Eddington read his recent paper it was assumed that the . turning point represented the change of the star from the gaseous state to the ! liquid (to be followed by the solid in due , course). It had previously been a diffuse, j gaseous 'giant'; but the relentless force ' 'of gravitation gradually crushed it into a liquid, when its particles could no longer move about freely, and thereafter ( it became a 'dwarf.' ' "Professor Eddington had traced these * changes mathematically, but found him- ' self compelled to recognise the existence of another controlling force besides ' gravitation, and, indeed, opposed to it, viz., the repulsive force which the radia- f tion of light exerts on all bodies, but ' I especially on small bodies. The particles | inside a star are drawn together by r gravitation, but radiation tends to keep them apart, though being always less than gravitation it can only delay its ' action and not overcome it. Professor , Eddington'e work further led him to the conclusion that in a star greater ' than a certain size radiation would bo j nearly balance gravity that the merest j shake would break the etar in two, ( which explained why we had not come across any stars greater than a certain * limit of mass. And, further, that the lower limit (also a fact of observation) £ could be explained by the comparative | insignificance of radiation-repulsion compared with gravity. In between 5 these limits, however,*lie assumed that , a star could have an arbitrary mass, which would determine its life history; if its mass were large it would pass through the whole series of changes, from M to B, and back from B to M. . But if the mass were small, it might . only rise from M to X before becoming liquefied and having to turn back to- ' wards M. The turning point would depend on the mass of the star, approximately retained as its characteristic throughout its history. ) Giants or Dwarfs. ] "Sow, perhaps, it is the simplest way i of introducing the change with which he startled us in March to cay that he now 1 suggests the same life history for every I star —the same track for all stars to I run on! They do not all join it at the < same point, owing to the accidents of 1 original size; a massive star will join i the track early, but on the new view it will gradually become less massive by < radiating itself away (for in modern i physics radiation is material), and will < thus arrive at the station where a less massive star is constrained to start. In i fact, Professor Eddington showed us a i diagram of the line of rails .(which in I technical terms is a curve connecting < luminosity with mass) with all known 1 stars clinging to them—'known , stars 1 being those for which the two necessary < elements had been determined—and t confessed how he had been bewildered s by finding that all stars, whether j 'giants' or 'dwarfs, , were on the rails, l which he thought only suitable for 'giants.' '' "And then he gave the revolutionary \ explanation which had occurred to him. 1 We had supposed giants and dwarfs to s be separated by liquefaction, meaning i that the particles inside the star had come too close together to move about < freely as in a gas. Perhaps, after all, < we had been wrong? What if the pro- < Eumed congestion were non-existent? The closeness of the atoma inside a star i could be estimated, and had. no doubt < been correctly estimated; but what if < they were atoms no longer? The fierce ! temperature (millions of degrees on our j scales) inside a star would doubtless 1 break up the atoms into their constituent electrons and protons, which are i so small compared with atoms that they I might have plenty of room when atoms 1 would be crowded. Sir Oliver Lodge fcas compared electrons in an atom to flies ' in a cathedral. The image helps us to I understand how we might have a city ' in which cathedrals were so close to- ' gether aa to incur the charge of overcrowding, whereas, if we abolished the ' bricks and mortar the few flies inside ' the ctahedrals would be liable to no such 1 suspicion.