2009

The field of a new neutron star

Round: Theory
Points: 10
Level: Bronze
Taught in: Section 10.1

Adapted from IOAA 2009 (Tehran), theory problem 10. We have restated it in our own words and kept the original data. The official answer rounds the field to 1.93 × 10⁶ T, and the data give 1.94 × 10⁶ T. The solution was last checked on 23 October 2026.

A main-sequence star of radius 4 solar radii and mass 6 solar masses has an average magnetic field of $10^{- 4}$ T. Find the strength of its magnetic field when it has become a neutron star of radius 20 km.

I solved it without the solution

AnswerThe field is $1.94 \times 10^{6}$ T. The mass of the star is not needed.

This problem also appears among the olympiad problems of Section 10.1, White dwarfs and neutron stars, which teaches the ideas it uses. Equation and figure numbers refer to the course.