Formation of “Blanets” in the Active Galactic Nuclei

Wada Keiichi (Kagoshima University)

Without doubt, planets are formed from proto-planetary disks around
stars, and more than four thousand exoplanets have been discovered until
now.  However, proto-planetary disks may not be the only site of
forming planets in the universe.  Recently we proposed a novel site for
“planet” formation, namely circumnuclear gas disks around supermassive
black holes (SMBHs).  Most galaxies harbour SMBHs whose masses are
ranged from a few million to billion solar masses.  Accretion disks
around SMBHs emit enormous energy owing to mass accretion to the
SMBHs, which are known as the `central engine’  of active galactic
nuclei (AGNs). They are believed to be surrounded by dense, dusty gas,
which obscures the emission from the accretion disks.  As a result,
there should be a co\ld dust disk beyond several parsecs from the AGN.
In Wada, Tsukamoto, & Kokubo (2019),  we investigated growth history
from sub-micron sized icy monomers to km-sized planetesimals in
circumnuclear disks around SMBHs, based on recent plausible theories
of planetesimal formation around stars. We improved this the model
this year in Paper II, including the effect of the radial drift of the
dust aggregates. We found that  “blanets” = black hole planets whose
mass is 100-1000 Earth masses could be formed around some AGNs.