I am interested in nearby binary systems in which a white dwarf (or a black hole) is in a short period of orbit with a main sequence star which it is consuming by accretion. As gravitational radiation causes the components to come closer together, gas from the envelope of the star passes across the inner Lagrangian point and falls in toward a disk circulating the collapsed object. A hot spot forms where the gas stream strikes the accretion disk. >From time to time an instability develops in the accretion disk and mass flows inward onto the surface of the white dwarf where it burns violently. If the mass of the white dwarf reaches the Chandrasekhar limit, a supernova explosion occurs. I am curious about how accretion disks work. The puzzle with disks is that there is no satisfactory physical model for the viscosity that is needed to transfer angular momentum outward through the disk.
Keith Horne and I made a three color map of an accretion disk in RW Trianguli by observing the eclipse of the disk by the companion star with a multicolor fast photometer. The picture we constructed is shown in Plate 1.
>From time to time I revisit an odd phenomenon in these systems for which no model or explanation exists. At times when the disk is unstable and mass is accreting onto the white dwarf, the system may emit a frequency coherent signal. The amplitude of the signal is rarely larger than 0.003 magnitudes and the frequency varies slowly over the course of several days. The maximum frequency that is observed is approximately equal to the frequency of revolution of particle in orbit at the surface of the white dwarf (0.1 Hz typically). An example of this signal that Roger Hildebrand, Earle Spiller, and I observed is shown in Figure 1.
Last Update: 6/23/2005