The supercritical accretion regime is very important for astrophysics.
In the first half-billion years just after our Universe was born,
supermassive black holes (quasars) began to appear and grow in centers
of young galaxies.
A unique set of linear polarization measurements in the spectrum of
the Seyfert galaxy Mkn 6 was obtained with the 6-meter telescope.
It was shown for the first time that the analysis of the polarization
angle dependence on the velocity across the hydrogen line profiles due
to the gas emission in the broad-line formation region near the massive
AGN allows to determine directly from observations the type of motion
in the broad-line formation region, which in the case of Mkn 6 turned
out to be Keplerian at distances less than 0.02 pc from the nucleus.
The lower mass limit determined for the supermassive black hole in
the center of the Mkn 6 galaxy is equal to 150 million solar masses.
High spectral resolution echelle spectroscopy of supergiants at the
post-ABG stage resulted in the formation of a sample of these objects
possessing a high infrared excess, an emission at 21 μm, and also large
overabundances of carbon and heavy metals, synthesized by the s-process
at the preceding AGB stage.