Galaxy formation by galactic magnetic fields

Galaxies exhibit a sequence of various morphological types, i.e., the Hubbl e sequence, and they are basically composed of spheroidal components (ellip tical galaxies and bulges in spiral galaxies) and disks. It is known that s pheroidal components are found only in relatively massive galaxies with M = 10(10)-10(12) M., and all stellar populations in them are very old, but th ere is no clear explanation for these facts. Here we present a speculative scenario for the origin of the Hubble sequence, in which the magnetic field s ubiquitously seen in galaxies have played a crucial role. We first start from a strange observational fact, that magnetic field strengths observed i n spiral galaxies sharply concentrate at a few microgauss for a wide range of galaxy luminosities and types. We then argue that this fact and the obse rved correlation between star formation activity and magnetic field strengt h in spiral galaxies suggest that spheroidal galaxies have formed by starbu rsts induced by strong magnetic fields. Then we show that this idea natural ly leads to the formation of spheroidal systems only in massive and high-re dshift objects in a hierarchically clustering universe, giving a simple exp lanation for various observations.