Schedule Aug 03, 2012
Gas Pile Up and Overflow in Circumbinary Accretion Disks: Type-I.5 Migration
Bence Kocsis (Harvard)

Many astrophysical binaries, from planets to black holes (BHs), exert strong torques on their circumbinary accretion disks, and are expected to significantly modify the disk structure. In this talk I will discuss a distinct regime, where the tidal barrier of the secondary causes a significant pile-up of gas outside of its orbit, which can lead to the closing of the gap. If the secondary is less massive than ~10^6 Msun, then the gap is closed before gravitational waves (GWs) start dominating the orbital decay. In this regime, the disk is still strongly perturbed, but the piled-up gas continuously overflows as in a porous dam, and crosses inside the secondary's orbit. The corresponding migration rate, which we label Type 1.5, is slower than the usual limiting cases known as Type I and II migration. The overflowing disk becomes several hundred times brighter in the optical bands than in AGNs with a solitary BH. Surveys such as PanSTARRS or LSST may discover the periodic variability of this population of binaries, and constrain the expected rates for future GW detections with LISA.

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