Limits on the neutrino magnetic moment from SN1987A

A neutrino magnetic moment greater than 10-12B, the Bohr magneton, would have important implications for gravitational-collapse supernovae. Also, it has been suggested that B10-10 might solve the solar neutrino problem. However, we show that the neutrino observations of SN1987A and general optical observations of supernovae set a firm upper limit of B<5×10-13. This limit is about 100 times better than the best experimental determination and previous astrophysical limits, and 10-20 times better than a previous limit based on big-bang nucleosynthesis.