Saturday 4 September 2021

Chandrasekhar

 This poem is a tribute to Chandrasekhar, probably one of the greatest astro-physicists ever. He was a prolific Astro-physicist probably an Astrophysical equivalent of Ramanujan the Indian mathematician. Like Ramanujan Chandrasekhar came to Cambridge to Study amongst other people Eddington who had demonstrated that Einstein's theory of relativity was correct by measuring the bending of light by the sun during an eclipse in 1919. Also he amongst others worked out the basic equations governing stellar structure which are still used today and was able to reproduce the Herzsprung Russell diagram. However Eddington did not have any idea what happened to a star when it died out. Chandresekhar using the relatively new ideas of statistical physics as applied to fermions and the Pauli exclusion principle worked out that there was a tension between the radiation pressure of a collection of fermions and their graviational attraction. he worked out that if the mass of the star was less than about 1.4 solar masses the resulting configuration would be stable and it's radious would much smaller than the radius when it was active. The matter would be ejected in a glorious explosion giving rise to a supernovae. The final state would be a white dwarf. All this was fine, but the consequence of this was that if the mass was greater than 1.4 solar masses the star would continue to collapse indefinitely and become a black hole (although that name hadn't been used back then). Chandrasekhar presented this idea at a meeting of the Royal Astronomical society. Somewhat unfairly even though Eddington knew about Chandrasekhar's results he waited until Chandrasekher had given his presentation to raise his objections. Of course Eddington's objectons, being who he was, prevailed and as a result the idea of black holes was suppressed for about 30 years. Chandrasekhar after he got his PhD moved to Chicago and continued to do work in Astrophysics and contributed to the ideas of stability in Fluids leading to some early investigations of phenomenon that would be later recognised as prefiguring chaos theory. In the end of course Chandrasekhar was vindicated. He wrote a book on Stellar structure which is still relevant today 

An introduction to the Study of Stellar Structure 

https://www.amazon.co.uk/Introduction-Study-Stellar-Structure-Astronomy/dp/0486604136/ref=sr_1_1?dchild=1&keywords=An+introduction+to+Stellar+structure+Chandrasekhar&qid=1630760779&s=books&sr=1-1


And hid definitive text on black holes including a full derivation of the relativistic equations governing the Kerr metric (one day I'll get round to understanding this :) )

https://www.amazon.co.uk/Mathematical-Theory-Classic-Physical-Sciences/dp/0198503709?asin=0198503709&revisionId=&format=4&depth=1

Although Chandrasekhar does include the health warning that at times the line of reasoning will be quite obscure as there are many leaps in some of the derivations. Perhaps with the aid of a symbolic manipulator such as Maple or Mathematics it might be possible to understand these derivations. 

There is also a summary of his work on instabilities in fluids 

https://www.amazon.co.uk/gp/product/B00C59C7ZA/ref=dbs_a_def_rwt_hsch_vapi_tkin_p1_i0

Finally a good general overview of the history of the development of Black holes and stellar stability is given by Kip Thornes book 

https://www.amazon.co.uk/Black-Holes-Time-Warps-Commonwealth/dp/0393312763

Anyway here is my tribute to this fine Astrophysicist 

                                   Chandrasekhar

 

                                            When a star collapses,

                                            There are no relapses.

                                            If it’s mass is really great,

                                            There is no final resting state.

 

                                            This idea made Eddington frown,

                                            After his great big put down.

                                            In science there was a great lack,

                                            Until people found holes that are black. 



 


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