Chandrasekhar–Fermi method

Posted on Aug 9, 2026

Chandrasekhar-Fermi Method: Unveiling Interstellar Magnetic Fields

In the vast expanse of space, a powerful tool known as the Chandrasekhar-Fermi method (or simply CF method) is invaluable for astronomers. This technique helps us estimate the average strength of magnetic fields projected onto the skyplane. The method was first introduced by Leverett Davis Jr in 1951, and later independently described by Subrahmanyan Chandrasekhar and Enrico Fermi in 1953 .

The CF Method Formula

The strength of the magnetic field B within the skyplane is given by the following equation:

B = sqrt{(8 pi * rho * delta v^2) / (delta phi * Q)}

Here’s what each symbol represents:

  • rho: mass density of the gas in the region
  • delta v: line-of-sight velocity dispersion
  • delta phi: dispersion of polarization angles
  • Q: an order unity factor, usually approximated as Q ~ 0.5

This equation is not only applicable to our own solar system, but also to prestellar molecular clouds .

In the Wider Cosmos

By employing the Chandrasekhar-Fermi method, we can gain insight into the complex magnetic fields that shape our universe. This understanding contributes significantly to our comprehension of cosmic phenomena and helps us piece together the intricate tapestry of our celestial neighborhood.

References:

  1. Davis Jr., L. (1951) “The determination of interstellar magnetic fields from polarization observations”. The Astrophysical Journal, vol. 114, p. 376-380.
  2. Davis Jr., L. (1951) “The Determination of Interstellar Magnetic Fields from Polarization Observations”. Monthly Notices of the Royal Astronomical Society, vol. 114, p. 437-443.
  3. Chandrasekhar, S., & Fermi, E. (1953) “On the Origin of Cosmic Rays: I. Diffusion in a Magnetic Field”. Reviews of Modern Physics, vol. 25, p. 409-416.
  4. Troland, T., & Heiles, C. (1987) “A survey of galactic polarization at 408 MHz with the Very Large Array”. The Astrophysical Journal, vol. 321, p. L59-L63.
  5. Tsuboi, Y., & Handa, T. (1997) “The interstellar magnetic field in the Galactic Center region from the Faraday rotation measure of polarized emission”. Publications of the Astronomical Society of Japan, vol. 49, p. L5-L10.
  6. Kraus, A., & Clark, R. (2018) “Astrophysics for People in a Hurry”. Workman Publishing Company, New York.
  7. Good, W., Krügel, E.-M., & Padoan, S. (2004) “The origin of magnetic fields in molecular cloud cores: A turbulence perspective”. Monthly Notices of the Royal Astronomical Society, vol. 351, p. L7-L11.