Astronomers are becoming increasingly aware of the fact that magnetic fields can have an important effect on the star formation in an interstellar cloud. Work in this area has been slow for two reasons. (1) As we have seen, measurements of the interstellar magnetic fields are very difficult. Until we have a good idea of field strengths, it is hard to estimate their effects. As we mentioned in the last chapter, observations of the Zeeman effect in HI yield field intensities of tens of microgauss in a number of clouds. (2) Theories that include magnetic fields are much harder to work out than those that don't. However, computer simulations of gravitational collapse in clouds with substantial magnetic fields are being carried out more routinely.

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