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S Chandrasekhar: Why Google honours him today | News | Al Jazeera
Subrahmanyan Chandrasekhar (19 October 1910 – 21 August 1995).
Subrahmanyan = patronymic (derived from his father's name)
Chandrasekhar = what we'd call a first name: use it
He was born in India, and in 1930, he went to the University of Cambridge in the UK. In 1937, he went to the University of Chicago, where he would spend the rest of his life.
He did work on a LOT of physical problems, showing great ability in the mathematics of those problems.
I must introduce the notion of equation of state: that's a material's pressure as a function of density, temperature, and other variables. Once one knows that, then one can calculate the structure of a self-gravitating object that is made of that material. Something that Chandra himself worked on.
He first worked on a simplified case, the "polytrope": pressure is some power of the density. With that under his belt, he took on the structure of white dwarfs. Matter in a WD is so compressed that its atomic structure is crushed out of existence and its electrons wander freely, matter called "degenerate matter". Metals are partially degenerate matter; only the atoms' outermost electrons behave like that. It's rather easy to calculate the equation of state of degenerate matter, and Chandra use that result to calculate the structures of WD's.
He discovered that WD's have a maximum mass, around 1.44 solar masses (strictly speaking, that * (2/(atomic mass units per electron))^2). Although degenerate matter can make enormous pressures, its pressure increase with density slows down as its electrons become relativistic, and it becomes too soft to support its own weight when self-gravitating (soft in a relative sense, of course!).
In 1935, astrophysicist Sir Arthur Eddington dismissed it as an absurdity. Unfortunately, he was a Big Name in the field, and while other astrophysicists discovered that Chandra was right, they were unwilling to challenge him. That is likely a reason why Chandra soon left the UK, and that was also a big setback for the field of relativistic stellar structure.
Chandra was eventually vindicated by the discovery of neutron stars and black holes, however.
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He did work on a variety of other problems, like:
Radiative transfer -- how light travels through a medium that scatters, absorbs, and reradiates it. That's very important for stellar structure, for obvious reasons, and it is also important for understanding spectral lines and the like.
Ellipsoidal figures of equilibrium -- a rotating self-gravitating object will have an ellipsoid as its equilibrium state. For slow rotation, it is a spheroid, while for fast rotation, it becomes a triaxial ellipsoid with two of its axes rotating. Imagine an American football spinning when on its side.
Stellar dynamics -- how stars behave when in clusters. I think that he analyzed this problem by treating stars as a sort of "star gas".
Brownian motion -- how objects move as they are randomly hit by molecules.
The quantum theory of the negative hydrogen ion -- a proton orbited by two electrons.
Hydrodynamic and hydromagnetic stability.
General relativity -- the mathematical theory of black holes, and also colliding gravitational waves. For BH's, he worked out such things as gravitational and electromagnetic wave modes near them.
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He was also the editor of The Astrophysical Journal, an important professional journal in that field, from 1952 to 1971, and in the last years of his life, he worked on explaining Sir Isaac Newton's "Philosophiae Naturalis Principia Mathematica" ("Mathematical Principles of Natural Philosophy", what science was called in the past). The original used lots of geometric arguments, while Chandra worked out versions of them using modern methods and modern notations. He published it as "Newton's Principia for the Common Reader", in 1995, the last year of his life.
Subrahmanyan Chandrasekhar (19 October 1910 – 21 August 1995).Subrahmanyan = patronymic (derived from his father's name)
Chandrasekhar = what we'd call a first name: use it
He was born in India, and in 1930, he went to the University of Cambridge in the UK. In 1937, he went to the University of Chicago, where he would spend the rest of his life.
He did work on a LOT of physical problems, showing great ability in the mathematics of those problems.
I must introduce the notion of equation of state: that's a material's pressure as a function of density, temperature, and other variables. Once one knows that, then one can calculate the structure of a self-gravitating object that is made of that material. Something that Chandra himself worked on.
He first worked on a simplified case, the "polytrope": pressure is some power of the density. With that under his belt, he took on the structure of white dwarfs. Matter in a WD is so compressed that its atomic structure is crushed out of existence and its electrons wander freely, matter called "degenerate matter". Metals are partially degenerate matter; only the atoms' outermost electrons behave like that. It's rather easy to calculate the equation of state of degenerate matter, and Chandra use that result to calculate the structures of WD's.
He discovered that WD's have a maximum mass, around 1.44 solar masses (strictly speaking, that * (2/(atomic mass units per electron))^2). Although degenerate matter can make enormous pressures, its pressure increase with density slows down as its electrons become relativistic, and it becomes too soft to support its own weight when self-gravitating (soft in a relative sense, of course!).
In 1935, astrophysicist Sir Arthur Eddington dismissed it as an absurdity. Unfortunately, he was a Big Name in the field, and while other astrophysicists discovered that Chandra was right, they were unwilling to challenge him. That is likely a reason why Chandra soon left the UK, and that was also a big setback for the field of relativistic stellar structure.
Chandra was eventually vindicated by the discovery of neutron stars and black holes, however.
-
He did work on a variety of other problems, like:
Radiative transfer -- how light travels through a medium that scatters, absorbs, and reradiates it. That's very important for stellar structure, for obvious reasons, and it is also important for understanding spectral lines and the like.
Ellipsoidal figures of equilibrium -- a rotating self-gravitating object will have an ellipsoid as its equilibrium state. For slow rotation, it is a spheroid, while for fast rotation, it becomes a triaxial ellipsoid with two of its axes rotating. Imagine an American football spinning when on its side.
Stellar dynamics -- how stars behave when in clusters. I think that he analyzed this problem by treating stars as a sort of "star gas".
Brownian motion -- how objects move as they are randomly hit by molecules.
The quantum theory of the negative hydrogen ion -- a proton orbited by two electrons.
Hydrodynamic and hydromagnetic stability.
General relativity -- the mathematical theory of black holes, and also colliding gravitational waves. For BH's, he worked out such things as gravitational and electromagnetic wave modes near them.
-
He was also the editor of The Astrophysical Journal, an important professional journal in that field, from 1952 to 1971, and in the last years of his life, he worked on explaining Sir Isaac Newton's "Philosophiae Naturalis Principia Mathematica" ("Mathematical Principles of Natural Philosophy", what science was called in the past). The original used lots of geometric arguments, while Chandra worked out versions of them using modern methods and modern notations. He published it as "Newton's Principia for the Common Reader", in 1995, the last year of his life.
