Abstract
Abstract In Wada et al. (2019), we proposed for the first time that a new class of planets, blanets, can be formed around supermassive black holes in the galactic center. Here, we investigate the dust coagulation processes and physical conditions of the blanet formation outside the snowline (r snow ∼ several parsecs) in more detail, especially considering the effect of the radial drift of the dust aggregates. We found that a dimensionless parameter , 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 collision. The formation timescale of blanets τ GI at r snow is, τ GI ≃ 70–80 Myr for α = 0.01 − 0.04 and M BH = 106 M ⊙. The mass of the blanets ranges from ∼20M E to 3000M E in r < 4 pc for α = 0.02 (M E is the Earth mass), which is in contrast with 4M E–6M E for the case without the radial drift. Our results suggest that blanets could be formed around relatively low-luminosity active galactic nuclei (L bol ∼ 1042 erg s−1) during their lifetime (≲108 yr).
Highlights
There is enough evidence suggesting that planets are formed in the circumstellar disks around stars
We found that a dimensionless parameter α = vt2/c2s, where vt is the turbulent velocity and cs 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 collision
In this follow-up paper of Wada et al (2019) (Paper I), we theoretically investigated a process of dust evolution around a super-massive black holes (SMBHs) in the galactic center
Summary
Planets around SMBH low-velocity collisions between dust particles promote sticking; the internal density of the dust aggregates decreases with growth (Okuzumi et al 2012; Kataoka et al 2013). In Paper I, we used the numerical experiments conducted by Wada et al (2009) on the collisions between the dust aggregates, wherein the critical collisional velocity (vcrit) scales with the mass md of the dust aggregates, as vcrit ∝ md1/4. Wada et al (2009, 2013) showed that the growth efficiency of the dust aggregates depends on the impact parameter of the collisions, and as a result, vcrit does not strongly depend on the mass of the dust aggregates, if off-set collisions are taken into account They concluded that vcrit 80 m s−1 for the ice monomers. This low critical velocity is one of the obstacles in the planet formation in circumstellar disks In this follow-up paper, we adopt vcrit 80 m s−1 as a constraint on the growth of the dust aggregates.
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