Supermassive primordial black holes at high redshifts

We consider some properties and possible observational manifestations of the very heavy primordial black holes (PBHs), with masses similar to (10(9) -10(10))M-circle dot. These black holes should be surrounded by the dense dark matter and baryonic halos even at early cosmological epochs. There are mechanisms as for radiation emission in the centers due to accretion and for deep absorption of relic radiation at the periphery of the halos. We calculate the absorption profile in the 21 cm line of atomic hydrogen by solving the equations of radiation transfer through the baryonic halo around a PBH. The calculations show that a spherical absorbing layer appears around the object, which can he observed with radio telescopes. Also, at some epochs, shock waves may form at the periphery of the objects. The accelerated charged particles can radiate in radio frequency band, so it is possible that these objects can explain the recently discovered radio circles.