I don't know of any. At least for ordinary materials, this experiment would seem nearly impossible. Take some material with a mass density of 1 gm/cm
3. Assume that it has a big internal magnetic field, say B=3000 G. The internal field energy density (in cgs units) is just B
2/8π, or about 400,000 erg/cm
3. That corresponds (via E=mc
2) to a mass density of about 4 10
-16 gm/cm
3. That's just way too small compared to the ordinary mass density to measure. (Sticklers will note that for a ferromagnetic material the net energy change may be negative rather than positive, etc., but this calculation gives the approximate scale correctly.)
Perhaps there are cases of extremely magnetic stars in which the magnetic field mass isn't negligible, so we'll update this if an astrophysicist knows of such a case.
Mike W.
(published on 12/08/2010)
