B. The Andromeda Nebula and its Companions
Although we do not have at the present anything very new to offer regarding the multiple system whose main member is Messier 31, it is of some importance to describe briefly what information might be obtained from a more thorough investigation of the relationship of M 31 to its companions.
There are two new observations made with the Schmidt telescopes on Palomar Mountain which are of importance in connection with our discussion of multiple galaxies. The first observation is that on long exposures with the 18-inch Schmidt Messier 31 appears to have a diameter of more than 12°, that is two to three times as large as any of the estimates which have recently been given. The 48-inch Schmidt plates revealed clearly that the elliptical companion NGC 205 is really an open barred spiral with very faint symmetrical arms, one of which points exactly at the nucleus of M 31. The extended arms of NGC 205 are possibly due to the tidal effects caused by the inhomogeneous and presumably strong gravitational field surrounding Messier 31. On the other hand it is of great importance to observe that the structure of the globular companion Messier 32 does not seem to be visibly affected by the proximity of the giant Messier 31. Under the circumstances it will be very important to make tests in order to decide whether or not M 31 and M 32 are really close neighbors or if they are components of an optical double separated by a considerable distance in the direction of the line of sight.
The multiple system of galaxies centered on Messier 31 offers perhaps the most important opportunities of any for future explorations of the mutual interactions of stellar systems. The Andromeda nebula and its physical companions constitute indeed the nearest system which is clearly delineated in its entirety. Being the nearest, the interactions of all of the member galaxies involved can be investigated in various independent ways. A first approach will explore the distribution of the individually resolvable stars. Secondly the distribution of gaseous masses can be studied through the use of the characteristics of emission line patches, while the distribution of obscuring matter can be investigated with well known methods. The new methods of radio astronomy should also prove a great tool in the case of the Andromeda nebula and its physical neighbors.