Bailyn's Fables: Chandrasekhar's Limit

First, we need to know a little something about white dwarfs and electron degeneracy pressure. You see, the normal way stars manage to not collapse into their incomprehensibly massive selves is thermal pressure. Basically, while gravity is pulling everything in, pressure is pushing everything back out, and so the two balance, at least, for a while. Eventually the star runs out of hydrogen in the core, which contracts, raising temperature of a shell of hydrogen outside the core, causing it to start fusing. This expands the star into a red giant, until all remaining hydrogen has been fused, making the star contract again.

What it doesn't do is collapse into a black hole. It seems that for high density objects other kinds of pressure arise. In this case it is electron-degeneracy pressure. Very, VERY basically, this is a result of no two particles being able to occupy the same space, and the pressure that results as the volume these particles are occupying decreases. Long story short is that this pressure fights against the gravity of the collapsing star, balancing at roughly the radius of the earth. This is called a white dwarf, and this is where we pick up the main subject of this post.

In the 1930s an Indian-American called Subrahmanyan Chandrasekhar discovered that electron-degeneracy pressure isn't always enough. If the mass of the star is more than 1.44 solar masses gravity overcomes the pressure and the star continues to collapse. He presented his findings to the Royal Astronomical Society. Upon finishing however Sir Arthur Eddington stood up and opposed Chadrasekhar's findings, stating:

 I think there should be a law of Nature to prevent a star from behaving in this absurd way!

A full account can be found in , pages 37-39. It is apparent that while he could understand the theoretical idea of a black hole, Eddington simply could not conceive of Chadrasekhar's findings, that beyond a certain mass a star could essentially collapse into nothing.The result of this was that a number of physicists who would otherwise have publicly agreed with Chadrasekhar did not, due to Eddington's status. Chandrasekhar spent the rest of his life holding to his beliefs, even until 50 years later when he finally got the Nobel Prize for his work.

The moral of this tale is that maybe one should believe their student, rather than their own intuition. Had Eddington allowed for Chandrasekhar's work to be possible, we might not have lost a good 40 odd years of research into black holes. It also demonstrates the dangers of being too convinced of one's own intellect. As Eddington got older he became more and more convinced that he could just guess the answer to questions using gut instinct, a method I imagine most of us would agree to be utterly useless scientifically.

Further reading

A review of the meeting in which Chandra presents his findings and Eddington tears them down. Relevent pages are 37-39
The highlights of Chandra's life
A brief biography, and image source for this post