What Happens When Star Meets Star.

When advocating this theory we may reasonably be asked to prove that the energy liberated when stars collide is actually sufficient to account for the observed behaviour of a Nova.

If a small mass is drawn from an immense distance to the surface of the Sun, it attains a speed of 386 miles per second. The same speed would be required to enable any body to escape from the Sun. This speed is, therefore, called the critical velocity of escape.

To leave the earth a projectile would have to start with a speed of at least seven miles per second. But this would not enable it to escape from the Solar System. It would either fall into the Sun or describe an orbit round it, according to the direction of the start.

Two stars like our Sun, drawn together by gravitation, would acquire before their surfaces met a relative speed of 386 miles per second. But the velocity destroyed in a slight graze would be little more than 193 miles per second. If, however, during the encounter the centres approach to within one radius of one another, the effective speed would be about 273 miles per second.

This implies an energy per unit mass 268 million times as intense as that of trains moving in opposite directions, each at 60 miles per hour. In a stellar collision this energy is transformed chiefly into heat, and is equivalent to 23 million calories per gram. The temperatures produced are most impressive.

Hydrogen molecules move about one mile per second when at a temperature of 200 degrees absolute, or 73 degrees below zero. If they move 273 miles per second, their temperature must be about

(Photo., G. W. Ritchey.)
Spiral Nebula Messier 51 Canum Venaticorum as seen through the 60 inch reflector at Mt. Wilson, April 7th–8th, 1910. Exposure, 103/4 hours.

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(Photo., Mt. Wilson Observatory.)
The Great Nebula in Orion as seen through the 100 inch reflector at Mt. Wilson, Nov. 19th, 1920.

15 million degrees. All other elements will be hotter still, lead being at 3,105 million degrees. If the molecules are broken up into separate atoms the speeds will be increased.

Now, since within the “Third Body” the elements are at such widely different temperatures, at every molecular or atomic encounter the heavier element must give energy to the lighter. Hydrogen thus is enabled to get up speeds exceeding a thousand miles per second, such as are disclosed in many of the spectrograms of Novae.