Magnetism and Gravity in the Cosmos
Most recent answer: 02/26/2018
- Andre Gillingham (age 26)
Trenton, Ontario, Canada
Magnetism is a big deal in the behavior of some objects, e.g. neutron stars. For the very large-scale cosmic phenomena, however, magnetism plays a negligible role. How can that be?
At long distances the gravitational field from a star or even a galaxy falls off as the square of the distance. The magnetic field falls of as the cube of the distance.
Also: On one hand, the total gravitational field of (for example) a galaxy is simply the sum of the gravity of its parts, That is, there is no cancellation. On the other hand, the contributions to the total magnetic field, produced by many small magnetic objects (eg, spinning stars) tend to cancel out.
So at large distances you can forget about the magnetic field, even when some of the objects involved have strong fields locally. This analysis is borne out by direct measurements of large-scale magnetic fields, which are very small.
(published on 02/26/2018)