India Environment Portal Knowledge for change

Setting new limits to scientific knowledge

• 14/07/1993

IN JANUARY 1935, the monthly meeting of the Royal Astronomical Society in London was unusually acrimonious. A young researcher from India, Subrahmanyam Chandrasekhar, had presented a paper in which he proposed a revolutionary theory regarding the fate of certain kinds of stars. The pre-eminent astrophysicist of the time, Arthur Eddington, had not only tried to disprove Chandrasekhar's theory but also ridiculed him. At the time no one took Chandrasekhar's theory seriously, but as is often the case, history proved Chandra (as he is known in the scientific community) correct.

Chandrasekhar and his Limit is an account of this revolutionary theory and meant for the serious student. Starting with a short biographical sketch of Chandra, the author takes the reader through the gamut of topics that are essential for understanding the Chandrasekhar limit.

Only recently has humankind begun to understand some of the basic mechanisms that make stars shine. Big blobs of hydrogen gas come together and start contracting. In the process, the inner part gets compressed and heated up to temperatures high enough for the hydrogen atoms to fuse into helium. This nuclear fusion releases an enormous amount of energy which stabilises the star's collapse against gravity. Then comes another stage of contraction and the process continues till there is only iron left in the core of the star.

Thermonuclear burning is then no longer possible and now the star is "dead". What happens to a star when it reaches this stage? This is the question that Chandra sought to answer. There are various scenarios possible, depending upon many factors such as mass and composition of the star. With a synthesis of the theories of relativity and quantum mechanics, Chandra was able to show that there is a maximum possible limit to the mass if the star (called a white dwarf) has to stabilise itself against the inevitable gravitational collapse. This mass, which is about 1.4 times the mass of our Sun, is now famous as the Chandrasekhar limit.

The book discusses a lot of background material. As a result, it ends up being too sketchy to help the beginner and too superfluous to interest the specialist. The style is chatty, which can get annoying at times. But the historical boxes are interesting and the illustrations are good. The book is also short on biographical details of Chandra, but then those are adequately covered in Kameshwar Wali's comprehensive biography, Chandra.

Chandrasekhar is undoubtedly one of the finest minds of our present century. His scholarship and the sheer breadth and range of his work is astounding. Even today, at 83, he is still as active as ever. This short book, though somewhat out of the reach of the interested lay reader, should certainly be read by all students of science for an inspiring account of the work done by one of our greatest scientists.

Shobhit Mahajan teaches physics at Delhi University