Formation of "Blanets" from Dust Grains around the Supermassive Black
  Holes in Galaxies
  In Wada, Tsukamoto, and Kokubo (2019), we proposed for the first time that a
new class of planets, "blanets" (i.e., black hole planets), can be formed
around supermassive black holes (SMBHs) in the galactic center. Here, we
investigate the dust coagulation processes and physical conditions of the
blanet formation outside the snow line ($r_{snow} \sim $ several parsecs) in
more detail, especially considering the effect of the radial advection of the
dust aggregates. We found that a dimensionless parameter $\alpha =
v_t^2/c_s^2$, where $v_t$ is the turbulent velocity and $c_s$ is the sound
velocity, describing the turbulent viscosity should be smaller than 0.04 in the
circumnuclear disk, to prevent the destruction of the aggregates due to
collisions. The formation timescale of blanets $\tau_{GI}$ at $r_{snow}$ is,
$\tau_{GI} \simeq$ 70-80 Myr for $\alpha = 0.01-0.04$ and $M_{BH} = 10^6
M_\odot$. The mass of the blanets ranges from $\sim 20 M_E$ to $3000 M_E$ in $r
< 4$ pc for $\alpha = 0.02$ ($M_E$ is the Earth mass), which is in contrast
with $ 4 M_E-6 M_E$ for the case without the radial advection. Our results
suggest that \textit{blanets} could be formed around relatively low-luminosity
AGNs ($L_{bol} \sim 10^{42}$ erg s$^{-1}$) during their lifetime ($\lesssim
10^8$ yr).
