Fragmentation of Kozai-Lidov Disks

TL;DR

This paper investigates how Kozai-Lidov cycles can induce gravitational instability and fragmentation in inclined disks around binary systems, potentially explaining giant planet formation.

Contribution

It demonstrates through hydrodynamic simulations that KL oscillations can trigger disk fragmentation even when the disk is gravitationally stable in the absence of such oscillations.

Findings

KL cycles can induce fragmentation in disks with Q > 2.

High initial tilt leads to disk oscillations and fragmentation.

Fragmentation may facilitate giant planet formation in binaries.

Abstract

We analyze the gravitational instability (GI) of a locally isothermal inclined disk around one component of a binary system. Such a disk can undergo global Kozai-Lidov (KL) cycles if the initial disk tilt is above the critical KL angle (of about 40 degrees). During these cycles, an initially circular disk exchanges its inclination for eccentricity, and vice versa. Self-gravity may suppress the cycles under some circumstances. However, with hydrodynamic simulations including self-gravity we show that for a sufficiently high initial disk tilts and for certain disk masses, disks can undergo KL oscillations and fragment due to GI, even when the Toomre Q value for an equivalent undisturbed disk is well within the stable regime (Q > 2). We suggest that KL triggered disk fragmentation provides a mechanism for the efficient formation of giant planets in binary systems and may enhance fragmentation of disks in massive black hole binaries.