No. 7.

On Binary and Multiple Stars.

The many thousands of stars which are revolving around each other in space supply a good reason for suspecting that they have originated in some commonly-acting cause, but as yet no general solution has been given to this important problem. Partial impact appears to offer at least one completely satisfactory solution. There are several arguments tending to show that if there are dark suns they may very probably have a greater proper motion than the luminous stare; therefore impact, approaching in its character to complete impact, is more likely in the case of bright stars than with dark bodies, for the reason of greater bulk due to heat and the smaller proper motions, allowing attractions to be more effectual. After impact this introduces two reasons why the two escaping pieces should return again from space. (1) The great mass of the coalesced body will develop a more effectual attraction, and (2) from the small proper motion, the independent kinetic energy upon which its escape depends will be very email. Thus partial collisions between luminous stars seem to offer many reasons why double stars should be developed. A typical case will suffice: supposing two stars, having a small proper motion in space, are brought within each other's attraction; after a long period they collide, a largo part of each coalesces, a new star is born, and the parts of the two stars not in each other's paths pass on in space; but the increased attraction due to the great mass of the coalesced piece causes their return. We now have a nebula and two variable stars; but, as these variable stars must return, it is possible that at the return there may be a fresh impact, resulting in one of those erratic variables which are so puzzling, but if the orbit is long, this is not likely, as the coalescence puts several forces in action which tend to convert the very eccentric orbits into circular ones. (1) The resistance of the gas itself. (2) Meeting the outgoing gas which selective escape would be sure to dissipate. (3) The lessened attractions on return due to the same actions. (4) The body in its forward motion will also have a rotation on its axis; the different frictions on its two sides so developed will carry the body outward. These forces, and several others, such as external pressure during impact, increased attraction at first escape, &c., all tend to render the orbit more circular: therefore, otter a few impacts, the bodies would certainly not strike. Generally not at all after the first. We have thus double stars of extremely eccentric orbits and with nebula between. This nebulous matter may be disposed of in several ways, it may be collected by the two bodies in their rotation and thus become more luminous, and finally settle down into a pair of binary stars. The nebulous mass may aggregate into one or more stars revolving around these two bodies. If this were the case, it should sometimes happen that the brightest star may have the smallest mass. A determination of the orbits of some of the multiple stars might prove if this is the case. This is the most probable origin of the multiple stars, but there is still another probability. In the impact of two approximately equal solid bodies, it is reasonable to suppose that the spindle-shaped mass, produced by the coalesced parte, should divide in several largo masses before the establishing of a uniform nebula, thus producing double or multiple nebulas which would settle down into stars of corresponding number; or even this may happen, and one or both of the two retreating bodies may return, In fact it does not seem possible that there could be any variety of multiple stars which partial impact is not competent to explain. In my next letter I shall attempt to show how the solar system may have originated by partial impact. The more detailed discussion of the mode in which eccentric motions may become almost circular, may help those to whom the mere statements of this hypothesis may appear difficult.