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The idea of a neutron star was considered to be highly speculative right up until 1967. Most astronomers believed that stars of average size, like our sun, up to stars that are very massive, finished their lives as white dwarfs. The theoretical properties of neutron stars were just too preposterous; for example, a thimble full would weigh about 100 million tonnes. A favored alternative proposal was that large stars would blow off their surplus mass a piece at a time until they got below the Chandrasekhar limit of 1.4 solar masses, when they could retire as respectable white dwarfs. This process did not entail the release of vast quantities of tiny particles devoid of electric potential that accompany star collapse as described in the cited Urantia Book quotation.
Acceptance of the existence of neutron stars gained ground slowly with discoveries accompanying the development of radio and x-ray astronomy. The Crab nebula played a central role as ideas about it emerged in the decade, 1950-1960. Originally observed as an explosion in the sky by Chinese astronomers in 1054, interest in the Crab nebula increased when, in 1958, Walter Baade reported visual observations suggesting moving ripples in its nebulosity. When sensitive electronic devices replaced the photographic plate as a means of detection, the oscillation frequency of what was thought to be a white dwarf star at the center of the Crab nebula turned out to be about 30 times per second.
For a white dwarf star with a diameter in the order of 1000 km, a rotation rate of even once per second would cause it to disintegrate due to centrifugal forces. Hence, this remarkably short pulsation period implied that the object responsible for the light variations must be very much smaller than a white dwarf, and the only possible contender for such properties appeared to be a neutron star. Final acceptance came with pictures of the center of the Crab nebula beamed back to earth by the orbiting Einstein X-ray observatory in 1967. These confirmed and amplified the evidence obtained by prior observations made with both light and radio telescopes.
The reversal of beta-decay, as depicted in (2) above, involves a triple collision, an extremely improbable event, unless two of the components combine in a meta-stable state--a fact not likely to be obvious to a non-expert observer which also indicates that the author(s) of the Urantia Paper was highly knowledgeable in this field.
The probable evolutionary course of collapse of massive stars has only been elucidated since the advent of fast computers. Such stars begin life composed mainly of hydrogen gas that burns to form helium. The nuclear energy released in this way holds off the gravitational urge to collapse. With the hydrogen in the central core exhausted, the core begins to shrink and heat up, making the outer layers expand. With the rise in temperature in the core, helium fuses to give carbon and oxygen, while the hydrogen around the core continues to make helium. At this stage the star expands to become a red giant.
After exhaustion of helium at the core, gravitational contraction again occurs and the rise in temperature permits carbon to burn to yield neon, sodium, and magnesium, after which the star begins to shrink to become a blue giant. Neon and oxygen burning follow. Finally silicon and sulphur, the products from burning of oxygen, ignite to produce iron. Iron nuclei cannot release energy on fusing together, hence with the exhaustion of its fuel source, the furnace at the center of the star goes out. Nothing can now slow the onslaught of gravitational collapse, and when the iron core reaches a critical mass of 1.4 times the mass of our sun, and the diameter of the star is now about half that of the earth, the star's fate is sealed.
Within a few tenths of a second, the iron ball collapses to about 50 kilometers across and then the collapse is halted as its density approaches that of the atomic nucleus and the protons and neutrons cannot be further squeezed together. The halting of the collapse sends a tremendous shock wave back through the outer region of the core.
The light we see from our sun comes only from its outer surface layer. However, the energy that fuels the sunlight (and life on earth) originates from the hot, dense thermonuclear furnace at the Sun's core. Though sunlight takes only about eight minutes to travel from the sun to earth, the energy from the sun's core that gives rise to this sunlight takes in the order of a million years to diffuse from the core to the surface. In other words, a sun (or star) is relatively "opaque" to the energy diffusing from its thermonuclear core to its surface, hence it supplies the pressure necessary to prevent gravitational collapse. But this is not true of Pauli's hypothetical "little neutral particles," postulated to exist since the early 1930's and known by the name neutrinos. These particles are so tiny and unreactive that their passage from our sun's core to its exterior would take only about 3 seconds. But did they exist?
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