Variable Stars.

39. The two stars that grazed would have a part cut out of each: this would expose the probably hot interior. Each star would entangle a portion of the other. This would increase the temperature and luminosity of the cut part of each.

40. The stars after collision would recover their sphericity chiefly by the molten interior welling up. This by momentum would overfill the space, and there would be a rhythmic tidal action, the molten lake overfilling and then sinking.

41. The retardation of the sheared stars by the entangled material would cause them to spin. This would act chiefly on the outer layers; the inside would tend to retain the original rotation of the star.

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42. Thus in the sheared stars there are three tendencies struggling with one another—(1) the original rotation, (2) the new rotation, (3) the tidal action.

43. But the new rotation would be a large component. We have therefore a star which rotates and shows us alternately its hot and cool sides. The old rotation and the tidal motion produce other fluctuations of intensity, and also inequalities of the rate of motion.

44. Evidently such a body as described would be a variable star, and for a time such stars would be in pairs.

45. Many variable stars are in pairs. It is so striking a phenomenon that the probability is one hundred sextillions to one against its being the result of chance.

46. The stars of these pairs would have a motion directed outward from each other. The spectra might show displaced lines, if so the displacement should be in opposite directions in the two stars.

47. Conduction, convection, tidal motion, and the contending rotations will tend to bring about equality of temperature. This condition of variability will consequently be a temporary page 16 one. The star will ultimately become of uniform luminosity. These characteristics are all of them known peculiarities of variable stars.

48. Convection is due to difference of density. This difference may result from differences of temperature, or of chemical composition or of both. The lake of fire in the sheared star will consist of heavier molecules than the remaining surface, and it will also be at a higher temperature. These two will tend to neutralize each other; so that equality of temperature due to convection will not be brought about quickly.

49. Therefore, although such variable stars will doubtlessly become uniform, it is surprising what a number of agencies there are tending to retain this inequality of temperature. On theoretical grounds it Appears that this condition of unequal heating may, as an extreme case, last thousands of years.