The existence of quasars at redshift z > 5 indicates that supermassive black holes were present since the very early times .
If they grew by accretion , the seeds of mass \gtrsim 10 ^ { 5 } M _ { \odot } must have formed at z \sim 9 .
These seed black holes may result from the collapse and dissipation of primordial gas during the early stages of galaxy formation .
I discuss the effects of magnetic fields on the fragmentation of cold gas clouds embedded into a hot diffuse phase and a virialized dark matter halo .
The field of 10 ^ { -4 } G ejected by supernova remnants can halt cloud break-up at 10 ^ { 4 } M _ { \odot } .
High star formation rates keep the clouds partially ionized , making ambipolar diffusion inefficient .
The magnetically-supported clouds collapse into black holes , which later spiral via dynamical friction into a central cluster with the total mass M _ { bh } \sim 6 \times 10 ^ { 6 } M _ { \odot } .
As the cluster collapses , the black holes merge emitting gravitational radiation that should be detectable by LISA .