IN STARRY SKIES

Evening Post, Volume CXVI, Issue 103, 28 October 1933, Page 15

IN STARRY SKIES

THE CAUSE OF THE CATASTROPHE

(By "Omega Centauri.")

At the end of his scholarly work on "The Spectrum of Nova Geminorum II" Mr. P. J. M. Stratton _ gjves a short • but very suggestive section on Physical Explanations. He tackles two problems: the nature of the initial catas--1 trop'he, and the subsequent,,development and motion of thq disturbed body or ■bodies. With,regard to the first problem he mentions the theories of Seeliger, Bickerton, Lockyer, Huggins, Deslandres, and Evershed. "Without going into any detail he gives the pride of place to Seeliger's suggestion that 'the outburst of a Nova is due to a ■f collisionibetween^ star and a nebula, ,and later he pronounces, n^ore definitely an favour of this hypothesis. No reference is made to the fatal objections that such an impact would not be sadden, would fail utterly tovacr count for the intensity of the explosion, and that if a star were heated in this way it would take millions of -■ years to cool. He does not point out the grotesque inadequacy of such explanations as a volcanic eruption on a cooling star or a clash of meteor swarms. In discussing the second problem he - refers to the views of Halm, v Deslandres, Wilsing Ebert, Julius, Duffield, Hale, and Kent. All through this discussion one feels that the only thing necessary to remove the difficulties that every_ one of the above astronomers, experiences is a recogni- "• tion of the peculiar properties of the third body. Stratton decides that the astonishing displacements of the lines im the complex spectrum are undoubtedly due to a Doppler effect. This means' that successive pulses or streams , of matter are pouring out with prodigi- . ous velocities from a. central disturbed ■ body, and moreover that theso en- , velopes' keep steadily expanding. As possible causes he mentions radiation pressure and electrical repulsion, but prefers the idea that the materials start " with hyperbolic velocities. Unfortunately he does not say how such veloei- ' ties are produced or how it is that the gravitational attraction of the star not only fails to reduce them, but even allows them to-be increased. Some of - the .authors-referred to are forced to postulate the action of unknown forces. On thoir 'hypotheses velocities of even a-thousand miles a second are inexplicable. To talk of.outrushes at such a speed as "convection currents" is ridiculous. So, with regard to the cause of of the catastrophe, Strattou gives no satisfactory explanation. But from an intensive study of the spectrum, he is able to tell us whatvhappens when the explosion : occurs. The successive ab- . sorption spectra show, that successive pulses or streams of matter are pouring • out-f rom. a central disturbed body. He regards these as jets or streamers issuing from different points and carried round by rotation. The alternations thus become natural, as the absorption, stage corresponds to the time in which a jet is pointed towards the observer. Without the clue provided by "selective atomic escape?' he has difficulty in accounting for'the gradual'-changei in. theelements concerned from metals such; as iron and titanium to non-metallic; gases such as oxygen, nitrogen, carbon,' and helium, and subsequently to the ~ still ■•.lighter ■neb,ttlium.:< He considers that' progressive atomic disintegration ■•. may explain the development of the '.• different spectral types. The simultaneous presence of an A and a. B type" spectrum was for a time regarded * by spectroscopists as indicating the ;: profenee of ; tw.o distinct bodies with ', different motions in the line of sight. It wHrb&remembeved---that- as soon .as. * spectrogram. reached New Zealand,. Professor Biekerton pointed out that

there was no indication in it of the colliding, stars, but that the spectrum 'was'exactly- that predicted for the "Third Body.'.' ; Until its intense splendour abated no evidence could be expected of tho presence of the wounded stars. Orthodox astronomers were led in quite a different, way to the couelusion, that the Nova spectrum is essentially that of a single very complex body. In every case the B type absorption spectrum, indicates a very high velocity towards our system, whilst the A type bright band spectrum gives little evidence of motion in the body as a whole. Then it was found that at a certain stage the ab- [ sorption. lines are doubled or trebled and: the bright bands show r very complicated structure. If different displacements represent distinct bodies at least four will be required to account for Nova Geminorum and still more for other Novae. "Local disturbances in a single body," Stratton states, "best fit the facts." But he adds that "the difficulty of the ouc-body hypothesis

lies.in explaining the origin and maintenance of tho enormous velocities observed." If a star encountered a> nebula the particles which fell on to the star would not be likely to have . velocities exceeding a few hundred miles a second. How could tho energy so transformed result in an outrush of enormous quantities of material at speeds of one or two thousand miles •a second? But as-we have shown repeatedly the production and mainten- ; ance of' such velocities daring the explosion of the Third Body are the natural results of known chemical and physical=laws. Gravitation ia drawing two stars together gives them a rela tive speed of four or five hundred miles a second. If the two are equal in mass half this, speed is transformed in the Third BodyJnto atomic heat agitation. The different elements then aro at widely different temperatures proportional to their atomic "weights/ Equalisation ..of temperature., results in very, high speeds.for.thfo lightest atoms, hydrogen atttaining one or two thousand i

miles a second. The initial speeds of the light elements exceed so greatly the critical velocity of escape from the comparatively small mass of the Third Body, that gravitation is powerless to make any appreciable reduction. We shall see that in the cases of two recent Novae the discs produced by the matter rushing out from the disturbed body have been actually observed and measured.. Stratton, writing in 1920, admits that the final theory of Novae cannot yet be written. But he sums up in favour of Seeliger's theory that streamers of glowing gas spread out from a central body after a collision with a quiescent dark cloud and that finally a planetary nebula is formed with a Wolf-Eayet star as a neuclus. This seems impossible to visualise. An ordinary star is usually moving less than a score of miles per second. As it approaches the stationary nebula it will draw towards it the nearer particles, which will approach at first slowly and then with increasing speed. The final velocity will depend y on the

mass and size, of the star^ but will b& measured in not more than hundreds of miles per second.: Without invoking the action of unknown forces how can an outrush be explained of comparatively vast masses sufficient to form a planetary nebula, with speeds many tinies as great as that of the falling nebulosity. Then again, the process would be a gradual one. A slowly increasing shower of nebulosity would fall on the star and the temperature of its surface would slowly rise. "When, the star became completely immersed in the nebula it would slowly gather up more and more of the material, the process continuing for many millions of years. Apparently there are innumerable stars at present immersed in nebulosity, but they do not behave as Novae. In order that the rise of ten thousand or a hundred thousand timeaf in brightness may takeplace in a few hours or a few days the nebula must have the dimensions comparable with that of a star. But to produce' an explosion of the Ob-

served intensity it must have the mass and the density of a star. Thus the nebula with which the sta* collides is nothing more or less than another star. Moreover, in the case of any typical Nova the collision is a grazing one. A direct collision may produce a giant star, but the, rise in brightness is then only about _ one magnitude, and it endures for millions of years. '