DONOVAN LECTURE

Evening Post, Volume CXIX, Issue 85, 10 April 1935, Page 15

DONOVAN LECTURE

STELLAR COLLISIONS

DEAD STARS REBORN

THE ENDURING UNIVERSE

The Concert Chamber of the Town Hall was well filled last evening, when Mr. A. C. Gifford, M.A.," F.R.A.S., delivered the Donovan lecture in astronomy. Lantern slides were used to illustrate the lecture. Mr. Giflord covered a wide field, dealing with novae, double' and variable stars, solar systems, and nebulae, the keen interest of his audience being indicated by the attention his remarks received. Before commencing his address, which was entitled "Celestial Encounters and the Life of the Universe," Mr. Gifford referred to the interest in astronomy in Wellington, and thanked the City Council for the use of the Concert Chamber and the generous advertising of the meeting. He was introduced to the audience by Mr. M. F. Luckie, chairman of the Observatory Committee of the City Council, who said that Mr. Gifford was a distinguished astronomer, his talents having led to his being selected as the first New Zealander to deliver one of the lectures provided for by the late Mr. Donovan, an Australian astronomer, who had left a sum of money to encourage interest in astronomy. Mr. Luckie referred to the Carter bequest, made 35 years ago, which gave £2000 as the nucleus of a fund for the establishment of an observatory. This bequest, at compound interest, had grown to £8000, and he expressed the hope that the interest shown in astronomy would lead to the Royal Society, which acted as trustee, putting the fund to the purpose for which it was intended. One of the chief objects of the Donovan Trust, said Mr. Gifford, was to encourage astronomical observation, especially amongst amateurs. Expensive . apparatus was not required for the study of the stars and a great deal of valuable work was being done in New Zealand by a number of young men who were gaining wide recognition. Although the heavens appeared to be filled with stars, the number visible to the naked eye was actually limited to about 1500 under good conditions. With a 100-inch telescope and the photographic plate it was possible to find millions beyond those visible to the average individual; it was possible to count sixteen hundred millions. Mr. Gifford explained how the spectroscope told the astronomer a great deal about the composition of the star. Astronomers were trying to form some conception of the way in which the perpetual youth of the universe was maintained. They were not content with enumerating1 a multitude of disconnected facts but were trying to arrange them into some intelligible order and to explain their significance. • Referring first' to the sun, Mr. .Gifford said it was difficult to realise-its grandeur and. the comparative insignificance of the earth. The earth was slightly larger than Venus and considerably larger than Pluto, Mercury, or Mars, but it was a dwarf beside Uranus and Neptune, which were pig-: mies when compared with Jupiter and Saturn. . .' ■' : MIGHTY SUNS. With very few exceptions, said Mr. Gifford, the twinkling points in the heavens indicated the existence of mighty suns. Usually only five planets were visible to the naked eye. The discoveries of recent years concerning stars still seemed incredible. The distances to many of the stars had been measured and their mass, density, and surface temperatures recorded. It had been found that each star had its own life/history, and the majority of them had been'arranged in regular sequence and classified. The stars varied, to a profound degree in temperature, density, size, and mass; but the same chemical, elements ekisted throughout the universe. Mr. Gifford described various types of stars and said that some Were still in their earliest youth while others were in the last stages of extreme old age. To astronomers there was an inevitable conclusion that there must be some mode of rejuvenation. It seemed probable that the number of bright stars was insignificant' in comparison with that of'the hosts that had sunk into darkness, to await revivification. Every body and every system in the universe was in a 'state of intense activity. This seemed to indicate the possibility of collision, but against this view astronomers drew attention to the vastness of space. Some regions were far more crowded than others, and up to the present no adequate allowance had been made for the influence of dark stars. Their enormous number would increase the probability of stellar encounters. FORMING NEW WORLDS. Occasionally an unfamiliar point bf light appeared in the sky, .telling of an event that was in reality the most stupendous that man was privileged to witness. The vast change in radiating power that made such a star visible took place generally in less than a week, and sometimes in a few hours. The best theory so far advanced for the.appearance of this point of light was the "encounter theory" of Professor A. W. Bickerton. He claimed that gravitational forces were the only known ones sufficiently powerful to produce the observed effects, and as soon as he .proceeded to examine certain types of stellar impact he realised that he had discovered many of the most cherished secrets of the heavens. Mr. Gifford discussed various factors in collisions between stars and the light spectra that followed, and concluded by describing the origin of a solar system from such a collision. In the whirling coalescence of two stars in conjunction gas and flying fragments were thrown off to develop into a new planetary system similar to the solar system of which the earth is a part. THE UNIVERSE IMMORTAL. "Those who deny the possibility, or minimise the importance of, celestial encounters, are compelled to picture a dismal, end for the whole universe," said Mr. Gifford. "We now get a glimpse of a possible way of escape. Stars live their lives and die, gradually radiating away their thermal energy and perhaps also a portion of their mass. But stellar collisions provide the means for rejuvenation. Partial impact strews space with atoms of the lighter elements, which find their way to the most barren regions, and gather up.radiation that would otherwise be lost. Whirling coalescencebuilds planetary systems that may afford homes for every kind of life. "Complete collision will transform a couple of dwarfs into a giant star and renew its life for thousands of millions of millions of years," Mr. Gifford continued. "But even with this renewal of stellar life we can' hardly picture an isolated galaxy enduring for ever because it is perpetually radiating its energy away. But just as stars are revivified by encounters with other stars, cosmic systems renew their youth by meeting other systems. At present astronomers are unable to peer further into space than 150,000,000 light years, but every increase, in power discloses more and' more of the marvellous systems that we call the spiral nebulae. We cannot yet know whether the millions of spirals form a single unit in a system, vaster still, but wei