  Gravity is nearly a universal constant in the cusp of an NFW galaxy halo.
Inside this external field an isothermal gas sphere will collapse and trigger a
starburst if above a critical central pressure. Thus formed spheroidal stellar
systems have Sersic-profile and satisfy the Faber-Jackson relation. The process
is consistent with observed starbursts. We also recover the M_BH vs. velocity
dispersion relation, if the gas collapse is regulated or resisted by the
feedback from radiation from the central BH.
