The Generation of Magnetic Fields and X-ray Observations

We show that strong magnetic fields can be generated at shock waves associated with formation of galaxies or clusters of galaxies by the Weibel instability, an instability in collisionless plasmas. The estimated strength of the magnetic field generated through this mechanism is close to the order of values observed in galaxies or clusters of galaxies at present, which indicates that strong amplification of magnetic fields after formation of galaxies or clusters of galaxies is not required. This mechanism could have worked even at a redshift of ~10, and therefore the generated magnetic fields may have affected the formation of stars at the early universe. This model will be confirmed by future observations of nearby clusters of galaxies. In this context, we also present the Japanese X-ray missions.