double galaxy

double galaxy

Two galaxies observed in close proximity. Physical doubles are spatially close pairs assumed to be in orbit about a common center of mass. They are known as a dumbbell galaxy when two elliptical galaxies of similar mass orbit each other in a common envelope. Optical doubles are widely separated pairs that appear close only because of a chance alignment along the line of sight. Although orbital motions cannot be directly observed, the relative radial velocities of galaxies in a gravitationally bound pair can be used to estimate their total mass, and hence their mass-to-luminosity ratio.
References in periodicals archive ?
Next in line is NGC 6041, another double galaxy with the designation VV 213.
NGC 2292 and 2293 comprise a double galaxy system with each member nearly identical in size, shape, and surface brightness, with the former perhaps the more condensed of the two systems.
The double galaxy M51 is only about 25 million light-years distant, but nudging my 10-inch scope 1/2 [degrees] southward brings into view a trio of galaxies more than four times farther away.