ChandraChandra

His life ,work and legacyHis life ,work and legacy

Early life

Subrahmanyan Chandrasekhar , known to the world as Chandra was born on October 19, 1910 in Lahore.

Nephew of Nobel-prize winning physicist C. V. Raman

Had most of his school education by private tuition

Graduated from Presidency College, Chennai with a degree in physics.(1930)

Chandra begins his stellar career

Publishes first scientific paper in the Proceedings of the Royal Society in 1928,at age 18!

Awarded a Government of India scholarship for graduate studies in Cambridge .

Receives PhD in December 1933(rotating self-gravitating polytropes)

On the ship to England, discovers Chandrasekhar limit.

Chandrasekhar limit

It is the maximum mass possible for a white dwarf star supported by electron degeneracy pressure.

Approximately 3 × 1030 kg, around 1.44 times the mass of the Sun.

Published in the Astrophysical Journal , in March 1931.

How a normal star works Heat generated by nuclear fusion of atoms of lighter

elements into heavier ones in a star's core pushes the atmosphere of the star out and balances the inward force of gravity.

Thus, a star is in equilibrium under the action of two opposing forces. As the star runs out of fuel, the atmosphere collapses back on the star's core.

If the star has a mass below the Chandrasekhar limit, collapse is limited by electron degeneracy pressure, resulting in a stable white dwarf.

Electron degeneracy pressure

Electron degeneracy follows from Pauli Exclusion Principle. No two electrons can occupy identical states.

As the star contracts, all the lowest electron energy levels are filled and the electrons are forced into higher and higher energy levels, in the order of increasing energy.

This creates an effective pressure, preventing further gravitational collapse.

White dwarf

Sirius B,is the closest white dwarf to the sun. It is a tiny star in orbit around the bright star Sirius.

The equation

Mch = Chandrasekhar mass limit = reduced Planck’s constant G = Gravitational constant C = speed of light Mp = mass of proton

The approximate equation for the Chandrasekhar limit is

If the limit is exceeded…….

If a star not capable of producing further energy had a mass above the Chandrasekhar limit, the pressure exerted by electrons would be unable to resist the force of gravity

Density increases beyond that of a white dwarf

A neutron star, or a black hole is the result

Stages in a star’s life

Main sequence –Hydrogen undergoes fusion to form helium

As hydrogen runs out star expands to become a red giant

If not very massive

White dwarf formed via planetary nebula

If massive

SUPERNOVA

Core collapses to form a neutron star

If enough mass is gained by accretion to go above Chandrasekhar limit

If still massiveBlack hole forms

Chandra’s insightChandra’s insight• Non-relativistically, a white dwarf may be

arbitrarily massive. • But, velocities of the electrons approach

the speed of light, and special relativity must be taken into account. The classical approximation is no longer appropriate.

• The result is that a limiting mass emerges for a self-gravitating, spherically symmetric body supported by degeneracy pressure.

The struggle

Upon presentation in a Royal Astronomical Society meeting in 1935, Chandra was criticized by Arthur Eddington.

Leading physicists unwilling to openly support his work although many approved privately.

Embittered, he moved to the United States .

Across the Atlantic

Initially, he worked at Yerkes Observatory, in Wisconsin.

Later moved to work on the University of Chicago campus, in 1937.

During World War II ,worked in the Ballistic Research Laboratories in Maryland.

In 1936,he married Lalitha Doraiswamy ,who was a fellow student at Presidency College.

At Chicago

He was appointed Morton D Hull distinguished service professor of the University of Chicago in 1952.

He and his wife became naturalized citizens of the United States in 1953.

Chandra was a popular teacher who guided over fifty students to their Ph.D.s ,including two Nobel Prize winners

His research work

Chandra published around 400 papers and published ten books, all of them classics in their respective topics.

His research interests were exceptionally broad.

Explored nearly all branches of theoretical astrophysics

His research topics

The areas in which he worked included : stellar structure, and the theory of white

dwarfs stellar dynamics, including the theory of

Brownian motion quantum theory of the negative ion of

hydrogen , the theory of planetary atmospheres, including the theory of the illumination and the polarization of the sunlit sky

hydrodynamic and hydromagnetic stability

equilibrium and the stability of ellipsoidal figures of equilibrium

general theory of relativity and relativistic astrophysics

mathematical theory of black holes

Astrophysical Journal

From 1952 until 1971 Chandra was editor of the Astrophysical Journal

Originally a local University of Chicago publication, it grew in stature to become national publication of the American Astronomical Society, then a leading international journal.

Nobel Prize

Awarded the 1983 Nobel Prize in Physics (shared with William Alfred Fowler) for his studies on the physical processes important to the structure and evolution of stars .

Upset that the citation mentioned only his earliest work, seeing this as a denigration of a lifetime's achievement.

Further Honours

Fellow of Royal Society(1944) Henry Norris Russell Lectureship (1949)

Bruce Medal (1952)Gold Medal of Royal Astronomical Society(1953)

Royal Medal of Royal Society(1962)National Medal of Science(1967)

Henry Draper Medal (1971)Copley Medal of the Royal Society (1984)

Chandra X-Ray Observatory

In 1999, NASA named the third of its four "Great Observatories'" after Chandrasekhar

The Chandra X-ray Observatory was launched and deployed by Space Shuttle Columbia on July 23, 1999.

End of an era Chandra retired in

1980 but continued to live in Chicago where he was made professor emeritus in 1985.

Aged 85,Chandra died from heart failure on August 21, 1995 and was buried in Chicago.

BibliographyBibliography

Chandrasekhar and his limit Chandrasekhar and his limit by G.Venkataramanby G.Venkataraman

Chandra:A biography of S.Chandrasekhar Chandra:A biography of S.Chandrasekhar by Kameshwar Waliby Kameshwar Wali

Chandra:The man behind the legend Chandra:The man behind the legend by Kameshwar Waliby Kameshwar Wali