The black tide model of QSOs

We examine the model for QSOs in which stars are tidally disrupted by a large black hole in a dense galactic nucleus, with the stellar material subsequently radiating as it spirals into the hole. We present detailed calculations of the growth and luminosity of a black hole in a nucleus of mass M/sub n/=3 x 10/sup 8/ M/sub sun/ and density 10/sup 7/ M/sub sun/ pc/sup -3/, including a stellar mass distribution, red giants, and partially disruptive encounters. If the rate of stellar disruptions is calculated in an nsigmav approximation, then a black hole with a=0.998 grows from M/sub H/=10/sup 5/ M/sub sun/ to M/sub H/=3 x 10/sup 8/ M/sub sun/ in 3.6 x 10/sup 9/ years, at which point the luminosity peaks at 2 x 10/sup 12/ L/sub sun/. This confirms the potential of the model to explain QSO luminosities. Black holes with aapprox. =0 achieve lower peak luminosities because the Roche limit disappears inside the horizon at smaller M/sub H/ than for rapidly rotating holes.A serious obstacle is that the number of stars in disruptive orbits is strongly depleted for M/sub H/approximately-greater-than10/sup 7/ M/sub sun/, according to an application of recent ''loss-cone'' theories. This prevents attainment of QSOmore » luminosities. Further study is needed to determine whether this obstacle can be removed.« less