The Peculiarities of Different Novae.

No two Novae are exactly alike, though all have certain essential family characteristics. The great differences observed in successive Novae are explained by the dissimilarities in the colliding stars and by the variations in the depth of the encounters.

We might expect that the collisions of gigantic stars would be more spectacular than those of stars like our sun, and that direct impacts would be grander than partial ones. Neither of these suppositions is correct. The most massive stars we know are all of enormous size and they have extremely low densities. Their encounters are slow, and the resulting temperatures comparatively moderate. Then, again, in a direct encounter the whole mass remains to restrain expansion. Professor Bickerton proved that, in a direct impact of equal stars, the energy is exactly sufficient to form, out of the two, a single star with double the diameter of either, and at the same temperature. Such an encounter, therefore, would merely double the luminosity whereas a grazing impact may multiply it hundreds or millions of times. This astounding increase in brightness is caused by the sudden expansion of the Cosmic Spark, due to its high temperature and small gravitational restraint. An impact may generally be considered a partial one if less than a third is struck from each star.

The magnitude and intensity of the explosion depend chiefly on the size and the density of the bodies involved. If the density remains unchanged the speeds developed in similar encounters are proportional to the diameters of the stars, the temperatures vary as the squares of the diameters whilst the duration of the encounter is unchanged. The clash of a pair of giants takes no longer than that of a pair of dwarfs.

If the diameters remain unchanged the temperature varies as the density, the velocity as its square root, and the duration of the encounter inversely as its square root.

To illustrate this let us compare or contrast an impact between a pair of giants like Antares, and another between two dwarfs like van Maanen's star, with one between two stars like our Sun. In the case of the giants, the velocity acquired is a quarter, and the temperature one-sixteenth, of those generated in a solar collision, and the encounter takes 109 days instead of 70 minutes. In a clash between the two dwarfs the temperatures would be twenty and the speeds nearly 4½ times those found in the case of Suns, and the encounter would be over in less than seven seconds. In such a collision if there was any lead in the “Third Body” it would be initially at 60,000 million degrees Centigrade.

We have considered only collisions between bodies exactly alike. A very improbable case. But the same principles apply in all encounters. Whilst variations in detail are infinite in number, all Novae have the same essential characteristics. We often hear of Novae and Super Novae. The latter are simply those in which temperatures and luminosities are thousands of times above the average, and the speed of the out-rushing gas about 4,000 instead of 1,000 miles per second.

When our telescopes are so much increased in power that we can detect the collisions of comparatively insignificant bodies, we may need a third class for those Novae that fall far below the average.

Meanwhile the theory we have advocated, and every other reasonable theory that is proposed, should be tested again and again by skilful observation and by rigorous mathematical calculation.

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