But if electrons are broken away from the atom these also become independent particles rendering support to the upper layers. A free electron gives just as much support as an atom does; it is of much smaller mass, but it moves about a hundred times as fast. The smashing of one silver atom provides 47 free electrons, making with the residual nucleus of the atom 48 particles in all. The aluminium atom gives 13 electrons or 14 particles in all; thus 4 aluminium atoms give 56 independent particles. The change from smashed silver to an equal mass of smashed aluminium only means a change from 48 to 56 particles, requiring a reduction of temperature by 14 per cent. We can tolerate that degree of uncertainty in our estimates of internal temperature;[4] it is a great improvement on the corresponding calculation for unsmashed atoms which was uncertain by a factor 4.
Besides bringing closer together the results for different varieties of chemical constitution, ionization by increasing the number of supporting particles lowers the calculated temperatures considerably. It is sometimes thought that the exceedingly high temperature assigned to the interior of a star is a modern sensationalism. That is not so. The early investigators, who neglected both ionization and radiation pressure, assigned much higher temperatures than those now accepted.
[Radiation Pressure and Mass]
The stars differ from one another in mass, that is to say, in the quantity of material gathered together to form them; but the differences are not so large as we might have expected from the great variety in brightness. We cannot always find out the mass of a star, but there are a fair number of stars for which the mass has been determined by astronomical measurements. The mass of the sun is—I will write it on the blackboard—
2000000000000000000000000000 tons
I hope I have counted the 0’s rightly, though I dare say you would not mind much if there were one or two too many or too few. But Nature does mind. When she made the stars she evidently attached great importance to getting the number of 0’s right. She has an idea that a star should contain a particular amount of material. Of course she allows what the officials at the mint would call a ‘remedy’. She may even pass a star with one 0 too many and give us an exceptionally large star, or with one 0 too few, giving a very small star. But these deviations are rare, and a mistake of two 0’s is almost unheard of. Usually she adheres much more closely to her pattern.
Fig. 5. IONIZATION BY X-RAYS
Fig. 6. IONIZATION BY COLLISION