Black Holes in Space by Patrick Moore

Author:Patrick Moore [Moore, Patrick]
Language: eng
Format: epub
ISBN: 9780855140328
Google: CInvAAAAMAAJ
Amazon: 0855140321
Goodreads: 1419554
Published: 2021-08-03T10:24:52+00:00

BLACK HOLES IN SPACE 69

Red Giant phase (as Mercury, Venus and probably the Earth will be destroyed in the case of the Sun), they will continue to orbit the dead star for the rest of time.

A typical White Dwarf is comparable in size with the Earth, and so has a radius of about 1/100 of the present radius of the Sun, or about 1 /30,ooo of that of the famous Red Giant star Betelgeux. If you think about the mass of the Sun compressed into a body the size of the Earth, then its density would be about a million times greater than the present density of the Sun - in other words, about a ton per cubic centimetre. This appears to be typical of White Dwarfs, and shows how matter can be compressed to densities far in excess of anything we could normally imagine.

There are many White Dwarfs to be seen in our Galaxy, and they probably represent the most common fate of stars. However, in 1931 Chandrasekhar showed that if a White Dwarf had a mass greater than 1.4 times that of the Sun, it could not - despite its great density -

resist further contraction due to gravity. This limiting mass is called the Chandrasekhar Limit. (Some recent work suggests that in practice the upper limit for a White Dwarf is 1.2 solar masses, but in this text we will keep to 1.4). Thus any star whose mass is greater than this cannot become a White Dwarf unless it gets rid of its excess mass in some way. If stellar matter is compressed to even higher densities than exist in White Dwarfs, one possibility is that a neutron star will be formed - that is to say, a body in which electrons and protons (negative and positive charges respectively) have been ‘squeezed’

together to form neutrons (electrically neutral particles).

Tremendous densities are then possible, and it seems that a typical neutron star could have a density of some 10 million tons per cubic centimetre. Because of these incredibly high densities, neutron stars are very tiny:

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