381 
352 ] The Origin of the Galactic System 
7 type*. Interpreted with the help of the information obtained in § 167, this 
means that the stars in globular clusters generate more energy per unit mass 
than stars of similar mass in the open clusters. On the view we are now 
considering this would mean that the former were born later than the latter, 
which accords with the formation of the globular clusters remaining intact 
while the open clusters are largely broken up. 
This view of the origin of the stars demands a modification of the simple 
view of stellar evolution which was propounded in Chapter vi. For, on 
the view we are now considering, Kruger 60 can never have been similar to 
Betelgeux, and Betelgeux will probably never be similar to Kruger 60. The 
latter star was born of the feebly-luminous matter which floated to the 
outside of the parent nebula, while Betelgeux was born out of the richly- 
luminous matter which collected at the centre of the nebula. The former 
calculation of 10 14 years as the age of Kruger 60 must be abandoned, since it 
was based on the assumption that the star had travelled the whole road from 
being a star similar to Betelgeux. 
Only the dynamical evidence as to the ages of the stars now remains 
valid. The evidence collected in Chapter xil indicates ages of the general 
order of 10 12 or 10 13 years, and this is in very good agreement with the 
evidence obtained from the rates of expansion and disintegration of star- 
clusters given in § 349 of the present chapter. There is no longer any 
evidence that any star is more than about 10 13 years old, and, indeed, a good 
many lines of evidence converge in indicating ages of the order of from five 
to ten million million years for the main mass of the stars, these ages being 
measured from the time at which the stars first condensed out of the parent 
nebula. The atoms ojf the parent nebula must have ages which are at least 
of the same order of magnitude, and as all the nebulae in the sky may be of 
the same age, there is no reason against supposing that the whole universe 
may have been created, or come into being, at the same instant. 
* Trumpler, Lick Obs. Bulletin, No. 361 (1925), p. 15.