Subrahmanyan Chandrasekhar: The Theorist of Massive Stars

From Madras to Stockholm: An Extraordinary Journey

Subrahmanyan Chandrasekhar (1910 – 1995) was an Indo-American astrophysicist whose work revolutionized our understanding of stellar evolution. Born on October 19, 1910, in Lahore (then in British India, now in Pakistan) into a Tamil Brahmin family, he was the nephew of physicist Chandrasekhara Venkata Raman (1888-1970), winner of the Nobel Prize in Physics in 1930.

After brilliant studies at Presidency College in Madras, he received a scholarship to continue his research at the University of Cambridge in 1930. It was during his boat journey to England, at just 19 years old, that he developed his theory on the Chandrasekhar limit (maximum mass that a white dwarf can reach before collapsing), a fundamental concept in astrophysics.

The Chandrasekhar Limit: A Controversial Discovery

In 1930, Chandrasekhar calculated that a white dwarf (final result of the evolution of intermediate-mass stars) cannot have a mass greater than 1.4 times the mass of the Sun (precise value: \(1.44 M_{\odot}\)). Beyond this limit, the star collapses under its own gravity to become either a neutron star (ultra-dense neutron star) or a black hole (region of spacetime where gravity is so intense that nothing can escape).

This theory, presented at a conference at the Royal Astronomical Society in 1935, was strongly criticized by Arthur Eddington (1882-1944), one of the leading figures in astrophysics at the time. Eddington called this idea "absurd," declaring that "there must be a law of nature to prevent a star from behaving in such an absurd way." This initial rejection deeply marked Chandrasekhar but did not prevent him from continuing his research.

Major Contributions to Astrophysics

Throughout his career, Chandrasekhar made fundamental contributions to several fields:

Academic Career and Recognition

After earning his PhD from Cambridge (1933), Chandrasekhar joined the University of Chicago in 1937, where he spent his entire career. He founded the famous Astrophysical Journal and trained several generations of astrophysicists. Among his most famous students were Eugene Parker (1927-2022), discoverer of the solar wind, and John N. Bahcall (1934-2005), pioneer in neutrino astronomy.

His contributions were eventually recognized through:

• The Nobel Prize in Physics in 1983 (shared with William A. Fowler) for his studies on the physical processes governing the structure and evolution of stars
• The Copley Medal from the Royal Society (1984)
• The National Medal of Science from the United States (1966)
• An asteroid (1958 Chandra) and a NASA space observatory (Chandra X-ray Observatory) named in his honor

Chandrasekhar's Legacy

Chandrasekhar's work profoundly marked modern astrophysics:

• Theory of compact objects:
  • Explanation of gravitational collapse of massive stars
  • Theoretical prediction of black holes before their observational discovery
  • Understanding of Type Ia supernovae (used as "standard candles" in cosmology)
• Mathematical methods:
  • Development of analytical techniques to solve stellar structure equations
  • Application of general relativity to astrophysics
• Educational influence:
  • Training of many influential astrophysicists
  • Writing of reference textbooks such as Principles of Stellar Dynamics (1942)

As Stephen Hawking (1942-2018) noted: "Chandrasekhar's work on the white dwarf limit was one of the first indications that general relativity could have dramatic physical consequences for astrophysical objects."

Major Works and Publications

Timeline of Key Discoveries