1919 .] 
Astronomical Notes. 
109 
ASTRONOMICAL NOTES. 
The Origin of New Stars (No. 2). 
The Source of the Energy. 
Our Sun is continually sending out radiant energy in every direction 
through space with such intensity that on each square centimetre of any 
surface directly facing it, at the distance of the Earth, 1-932 gramme calories 
fall each minute.* This implies that over 575,000 calories per minute pass 
through each square inch of the Sun’s surface — enough to raise 10 pints 
of water from freezing to boiling point. Novae that have been observed 
exceeded the Sun as a source of radiant energy at least 10,000 times. They 
rose in a few hours from invisibility or comparative insignificance to this 
marvellous state of radiant activity. Any theory as to the origin of new 
stars must therefore account in a satisfactory manner for this tremendous 
and astonishingly rapid transformation of energy. The inadequacy of 
“ sun-spots on a vaster scale,” “ volcanic eruptions from the interior fur¬ 
naces of a crusted sun,”f and even of chemical action, as possible causes of 
such phenomena is at once apparent. 
If the body consisted entirely of hydrogen and oxygen in the exact 
proportions necessary for complete combustion the heat evolved during the 
explosion in each gramme of the mixture would be only about 3,800 
calories ; if it consisted entirely of dynamite it would be 1,321 calories. 
Quite apart from the extreme improbability of any such chemical action, 
the quantities of heat involved are insufficient to account for the observed 
facts. The only cause so far suggested that is able to do so is some form 
of collision. The energy transformed into heat in this case being directly 
proportional to the square of the velocity destroyed, there is practically no 
limit to the temperature that may be produced. The velocity required to 
produce any particular thermal effect is easily calculated from the formula 
Kinetic energy = \mv 2 
wdiere m is the mass and v the velocity. 
For example, to raise the temperature of water 1° C. a velocity of 
approximately 100 yards per second must be destroyed. Two express 
trains moving with a velocity of one mile per minute and meeting head 
on, if all their kinetic energy was transformed into heat, would generate 
sufficient to raise the temperature of an equal mass of water ~° C. 
Now, a body drawn from an infinite distance to the Sun’s surface would 
acquire a velocity of 380 miles per second, or 22,800 times that of an 
express train. Its kinetic energy would therefore be 519,840,000 times as 
great. If its specific heat were unity its temperature would be raised more 
than 45,000,000° C., and if its specific heat were 0-03 it would be raised 
over 1,500,000,000° C. 
In the case of two bodies like our Sun drawn together from rest at 
stellar distance—say, as far apart as our Sun and a Centauri—the impact 
would begin when their centres were a Sun’s diameter apart. At that 
moment the kinetol, or kinetic energy per unit mass, would be only half 
what it would be if their centres were a radius apart, and half the work 
* Companion to the Observatory, 1919, p. 32. 
f Flammarion. 
