  We investigate the steady spherically symmetric accretion in the combined
potential of a central black hole and a dark matter halo. For the halo, we
consider a Hernquist and an NFW potential and calculate the critical points of
the flow. We find that the trans-sonic solution to the centre is not possible
without a black hole, whereas two types of trans-sonic solutions are possible
in its presence. We also derive the mass accretion rate for a black hole at the
centre of a dark matter halo. Our results indicate two phases of accretion. The
first is an initial phase with a low accretion rate that depends on the black
hole mass, followed by a second phase with a high accretion rate that depends
on the halo mass. In the second phase, the black hole mass increases rapidly to
supermassive scales, which explains the existence of quasars at redshift $z\ge
6$ and also the recently detected supermassive black holes (SMBHs) by the James
Webb Space Telescope (JWST). Further, we calculate the evolution of the
Eddington ratio for growing black holes. The accretion is mostly sub-Eddington
except for a short super-Eddington episode when the mass accretion rate
transitions from low to high. However, during that episode, the black hole mass
is likely inadequate to hinder accretion through radiative feedback.
