2004 ASTRONOMY & ASTROPHYSICS - Indian Academy of Sciences

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CHAPTER 2 The Present Revolution in Astronomy This is undoubtedly the Golden Age of astronomy and astrophysics. With the advent of the space age, unprecedented progress has been made during the past thirty or forty years. One is witnessing a great revolution in astronomy. Every now and then, questions that have remained meaningless, or considered frivolous, acquire meaning within the premise of science. And this constitutes a scientific revolution. The revolution that was unfolding at the dawn of the twentieth century concerned the nature of the stars. By the middle of the 19 th century, this question had acquired scientific significance despite the assertion of the positivist philosophers that it was in the nature of things that we shall never know what the stars are. By the 1930s one had understood a great deal about what the stars are, and why are they as they are. The great new question that arose at the beginning of the last century concerned the size and the nature of the astronomical Universe. With Hubble’s estimate of the distance to the Andromeda Nebula, it became clear that the great spiral nebulae were galaxies in their own right, that the Universe contained billions of galaxies and that the building blocks of the Universe were clusters of galaxies. In parallel a great revolution was taking place concerning the ultimate fate of the stars. Stars support themselves against gravity because they generate energy in their cores. What will happen when the nuclear reactor in the centre fails? The resolution of this question by R.H. Fowler and S. Chandrasekhar in the late 1920s and early 1930s required the new quantum theory. Indeed, this was the first application of the newly discovered A cluster of galaxies (Abell 2218). Courtesy: HST/NASA 7
THE PRESENT REVOLUTION IN ASTRONOMY stars, just as there is a maximum mass for white dwarfs. It became clear that sufficiently massive stars will therefore end their lives by becoming black holes. The first conclusive evidence for such stellar mass black holes was found in 1973 with the discovery of the X-ray binary Cygnus X-1. And thus began the exciting era of supernovae, neutron stars and black holes, the era of high energy astrophysics. Mass-Radius relation for the planets and White Dwarfs, from “The Birth and Death of the Sun” by George Gamow (1945). The words for mass and radius are, to quote Gamow, “in Dr. Chandrasekhar’s original Tamil”. quantum statistics by Fermi and Dirac. For a while it seemed that all stars will find ultimate peace as planetary sized white dwarfs. This hope did not last long because Chandrasekhar soon showed that white dwarfs more massive than about 1.4 times the mass of the sun cannot be stable. What then is the ultimate fate of the more massive stars? By the end of the 1930s it became clear that massive stars will collapse when they eventually develop degenerate cores, and when such cores grow to the limiting mass of 1.4 M . It was predicted by Baade and Zwicky in 1934 that the result of such a collapse will be the formation of a neutron star, accompanied by a supernova explosion. Based on very general considerations, it was predicted that such neutron stars will have masses ~ 1.4 M , that their radii will be about 10 kilometres, that they will be endowed with very strong magnetic fields ~ 10 12 Gauss and that they will be rapid rotators. All these prescient predictions came true with the discovery of pulsars by Jocelyn Bell and her collaborators in 1967, and the subsequent discovery of a fast pulsar in the Crab Nebula. In 1938 Oppenheimer and Volkoff demonstrated that there must be a maximum mass for neutron The other great question which acquired meaning during the last century is perhaps the grandest of all questions: “was there a beginning”? The beginning of this revolution was in the 1920s when Hubble discovered that the clusters of galaxies were systematically receding from us with velocities that are linearly dependent on their distances from us. If taken literally, this would imply that in the distant past the clusters of galaxies must have been closer together. Indeed, Georges Lemaitre proposed that the Universe must have once been a primeval atom. In the 1940s George Gamow took the bold step of taking all this seriously and making far reaching predictions. The most important of these was the prediction that the Universe today must contain the relic of the primeval radiation and that the temperature of this all pervading radiation must be a few degrees Kelvin. But not many took all this seriously, although this was the only scenario that could explain the observed helium in the Universe. The reason for this scepticism was that Gamow’s conjecture represented an extrapolation into the unknown. For one thing, he generalized the local expansion that Hubble had detected to imply a Universal expansion. He then extrapolated backwards in time into a domain where one didn’t know the laws of physics. The question of the origin of the Universe could not yet be posed rigorously within the premise of the existing theories. But this 8
Page 1 and 2: ASTRONOMY & ASTROPHYSICS A Decadal
Page 3 and 4: This publication of the Academy on
Page 5 and 6: Preface The Indian Academy of Scien
Page 7 and 8: The Academy Committee for Astronomy
Page 9 and 10: h e P a n e l s Theoretical Astroph
Page 11 and 12: C H A P T E R 1 Executive Summary
Page 13 and 14: EXECUTIVE SUMMARY The recommendatio
Page 15 and 16: EXECUTIVE SUMMARY feasibility study
Page 17: C H A P T E R 2 The Present Revolut
Page 21 and 22: THE PRESENT REVOLUTION IN ASTRONOMY
Page 37 and 38: A large eruptive prominence in HeII
Page 39 and 40: SOLAR PHYSICS • Detailed study of
Page 41 and 42: SOLAR PHYSICS Nainital Observatory
Page 43 and 44: SOLAR PHYSICS Some Possible New Ini
Page 45 and 46: SOLAR PHYSICS Telescope and the Hel
Page 47 and 48: C H A P T E R 4 Optical, Infrared &
Page 49 and 50: OPTICAL, INFRARED & ULTRAVIOLET AST
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One of the 30 antennas of the GMRT
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RADIO ASTRONOMY India’s location
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RADIO ASTRONOMY The first telescope
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RADIO ASTRONOMY Central Electronic
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RADIO ASTRONOMY • Resolution of t
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RADIO ASTRONOMY Some recommendation
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C H A P T E R 6 High Energy Astrono
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HIGH ENERGY ASTRONOMY 100 cm 2 area
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HIGH ENERGY ASTRONOMY Areas of Rese
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HIGH ENERGY ASTRONOMY remnant — E
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HIGH ENERGY ASTRONOMY detectors, an
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HIGH ENERGY ASTRONOMY Gamma Ray Ast
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HIGH ENERGY ASTRONOMY A gamma ray b
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HIGH ENERGY ASTRONOMY Cosmic Rays T
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HIGH ENERGY ASTRONOMY from Hyderaba
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HIGH ENERGY ASTRONOMY • Solar con
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HIGH ENERGY ASTRONOMY nuclear compo
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HIGH ENERGY ASTRONOMY New initiativ
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C H A P T E R Theoretical Astrophys
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THEORETICAL ASTROPHYSICS • The di
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THEORETICAL ASTROPHYSICS There has
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THEORETICAL ASTROPHYSICS 5. Equatio
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C H A P T E R Gravitation and Parti
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GRAVITATION AND PARTICLE ASTROPHYSI
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C H A P T E R Recommendations 9
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RECOMMENDATIONS different aspects s
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RECOMMENDATIONS was installed there
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RECOMMENDATIONS Keeping in mind the
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RECOMMENDATIONS The 1 m telescope a
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RECOMMENDATIONS as the technology t
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RECOMMENDATIONS The committee appre
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RECOMMENDATIONS • All Sky Monitor
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RECOMMENDATIONS using our facilitie
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RECOMMENDATIONS • The committee s
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List of addresses Radio Observatori
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S.N. Bose National Centre for Basic
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Indian Academy of Sciences C. V. Ra
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2004 ASTRONOMY & ASTROPHYSICS - Indian Academy of Sciences

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