Motion around a source whose luminosity changes

Abstract

This paper examines the motion of objects affected by changing radiation pressure from a central source. The orbits turn out to be generally unstable. Either the objects fall inward toward the source, or they are ejected from the system. If the radiation pressure has a component which flucturates in time with a dynamical frequency ..omega..>0.845 and relative amplitude ..cap alpha.., circular orbits become unstable on a time scale tau/sub asterisk/approx. =..omega../..cap alpha.. (in dimensionless dynamical units). If the fluctuation spectrum contains an angular variation of amplitude ..cap alpha.. and frequency n..cap omega.. such that n..cap omega..approx. =1 with n an integer, then it leads to unstable motion on an angular time scale theta/sub asterisk/approx. =1/a radians. If the fluctuations are stochastic with a white noise spectrum having variance sigma/sup 2/, then orbits are unstable with a growth time scale sigma/sup -2/. These time scales can be quite short even for small luminosity fluctuations. Under many astronomical conditions they will dominate classical radiation-orbit interactions such as the Poynting-Robertson effect. These unstable, time-dependent motions may be important in understanding various aspects of accretion disks around black holes and neutron stars, planetary nebulae, the distribution of material around rotating and variable stars, themore » evolution of the proto-solar system, and the orbits of large, low-mass (e.g., artificial) satellites around the Sun.« less