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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" (as per The Urantia Book, p.464) 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 the little neutral particles, known since the mid 1930's by the name neutrinos. These particles are so tiny and unreactive that their passage from our sun's core to its exterior takes only about 3 seconds.
It is because neutrinos can escape so readily that they have a critical role in bringing about the star's sudden death and the ensuing explosion. Neutrinos are formed in a variety of ways, many as neutrino-antineutrino pairs from highly energetic gamma rays and others arise as the compressed protons capture an electron (or expel a positron) to become neutrons, a reaction that is accompanied by the release of a neutrino. Something in the order of 1057 electron neutrinos are released in this way. Neutral current reactions from Zo particles of the weak force also contribute electron neutrinos along with the 'heavy' muon and tau neutrinos.
Together, these neutrinos constitute a "vast quantity of tiny particles devoid of electric potential" that readily escape from the star's interior. Calculations indicate that they carry ninety-nine percent of the energy released in the final supernova explosion. The gigantic flash of light that accompanies the explosion accounts for only a part of the remaining one percent! Although the bulk of the neutrinos and anti-neutrinos are released during the final explosion, they are also produced at the enormous temperatures reached by the inner core during final stages of contraction.
The opportunity to confirm the release of the neutrinos postulated to accompany the spectacular death of a giant star came in 1987 when a supernova explosion, visible to the naked eye, occurred in the Cloud of Magellan that neighbors our Milky Way galaxy. Calculations indicated that this supernova, dubbed SN1987A, should give rise to a neutrino burst at a density of 50 billion per square centimeter when it finally reached the earth, even though expanding as a spherical 'surface' originating at a distance 170,000 light years away. This neutrino burst was observed in the huge neutrino detectors at Kamiokande in Japan and at Fairport, Ohio, in the USA. lasting for a period of just 12 seconds, and confirming the computer simulations that indicated they should diffuse through the dense core relatively slowly. From the average energy and the number of 'hits' by the neutrinos in the detectors, it was possible to estimate that the energy released by SN1987 amounted to 2-3 x 1053 ergs. This is equal to the calculated gravitational binding energy that would be released by the collapse of a core of about 1.5 solar masses to a neutron star. Thus SN1987A provided a
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