A spherical particle, moving through an isotropic radiation field, will generally experience a small force that decreases its velocity because the Doppler effect causes a difference of radiation pressure between the front and back side of the particle. However, if the radiation is monochromatic, it is possible that certain particles, because of diffraction, can also absorb momentum from the radiation and increase their velocity. Numerical estimates are made to find the maximum possible effect of the radiation force on the velocity of a particle moving through an isotropic radiation field, such as that which exists inside a galaxy where the radiation from the stars is considered to be isotropic. These estimates indicate that the effects of this radiation generally take place over periods of time that are comparable to the age of the galaxies or longer.
DAVID SAVICKAS, "Dynamical Effects of Isotropic Radiation on Spherical Particles," J. Opt. Soc. Am. 60, 1240-1245 (1970)