Alpha Omega

It is not within the capacity of this book, nor is it important to its purpose, to give a detailed and complete description of the evolution of galaxies, stars, star clusters and solar systems. Nor is it the purpose of this trilogy to answer the numerous questions concerning the many anomalies of the celestial world and the earth sciences. Besides, most of this information can easily be found by searching through the many different books that deal with the origin and explanation of such things.

One should suffice it to say that all celestial bodies are created either directly or indirectly from basically the same process, which is by the gravitational contraction and fragmentation of a giant, interstellar cloud of hydrogen, helium, and subatomic particles.

Nuclear reactions in first generation stars form the heavier elements in successive stages. Hydrogen is formed into helium, which is then formed into carbon. Neon is then formed from carbon. Oxygen, silicon and other elements up to iron are then formed. Finally, iron is formed before the star explodes in a supernova, by which those elements heavier than iron are formed.

Second generation stars are created from the stellar debris of the supernova of first generation stars. Scattered in the arms of spiral galaxies, such as the Milky Way, and in the interstellar areas of elliptical and irregular galaxies, this cosmic debris forms into gigantic clouds of gas and dust, consisting mostly of hydrogen and helium with lesser amounts of the other elements. This “chemical soup” is widely dispersed initially and the gas and dust particles move randomly about. Collisions between particles are frequent.

Never-the-less, the formless, disorganized molecular cloud eventually comes under the control of gravitational forces and it begins to collapse in upon itself. The net results of the collisions and continued contraction molds the nebular into a huge, rotating sphere with the higher concentrations of matter closer to the center. One may obtain an idea of what this would look like by a vigorous and random stirring of a large bowl of vegetable soup and then pausing to observe its motion. The net results will be a circular rotation of the soup.

At this point the two opposing forces of gravitational attraction and internal pressure within the nebular will compete for dominance in molding and directing its future. However, the law of the conservation of angular momentum dictates that it will rotate faster as it is contracting. The increased rotation plus centrifugal force will compel the cloud to flatten at the poles and a disk will form in the equatorial plane of the mass. The disk will expand and slowly pick up rotational speed. Heat and pressure will decline in the expanding disk — the pressure will be absorbed as the disk expands while the heat will be radiated into space as infrared radiation.

Meanwhile, the innermost area of the nebular will capture most of the matter and have a relatively rapid collapse. Continued contraction of the central area will ensure a much greater concentration of matter there. This will further build up internal pressure and raise the temperature of the core still higher. Soon, as gas and dust continue to accumulate toward the central area, the density of the core will be high enough to prevent the radiation from escaping from there.

Eventually the nebular will begin to glow, at first in the infrared wavelengths and then, after nuclear reactions begin, in the visible wavelengths. But stabilization will not be reached in the proto-star until enough heat and pressure are built up to ignite continuous nuclear reactions. Until such time, gravitational contraction will persist and the proto-star will continue to get hotter.

While the central part is collapsing, the relatively cold disk will continue to slowly pick up rotation speed. The inner parts of the disk will revolve faster than the outer parts, breaking the disk into distinct rings or individual disks.

All this will continue until such time that there is an internal source of energy high enough to balance the gravitational contraction. This is when the star ignites its nuclear furnace. After continuous nuclear reactions take place within its interior one may then say that “the star is born,” which places it among that group of stars known as main sequence stars.

At this time the newly formed star will still be surrounded by a large envelope of gas, dust and ice crystals. However, solar winds coming from the star will heat this envelope and cause it to disperse to the outer edges of the system.

Here the envelope will cool and form into two rings of icy material at the outer edges of the system. These are a Kuiper Belt, which is just beyond the orbit of Pluto in this solar system, and an Oort Cloud, which is far beyond the solar system. The Kuiper Belt forms the raw material for short period comets and the Oort Cloud is believed to the source for longer period comets.

Before a second generation star is born, the nebular is an extremely cold and dark molecular cloud of elements, most of which are combined in ices of ammonia, methane, and water. These are mixed in with compounds of hydrocarbons, silicates, ferro-silicates and other ferrous compounds. In the central area of the nebular the heat and pressure will eventually cause this soup to return to a gaseous state but in the disks this chemical stew becomes a great ice slush as it revolves around the proto-star.

Because the inner portions of the disks will have a shorter revolutionary course to travel than the outer portions, this would cause each disk to revolve at different speeds. This in turn would cause them to develop eddies within each, which will act as central collection areas for future planet formation. At first, the ices act as a bonding agent, holding the particles together. As the dust to boulder size pieces revolve around the proto-star they constantly collide with one another. The heat produced by these collisions temporally melts the ices and when they re-freeze they are accreted into larger pieces.

They continue to collide with one another, shattering and then accreting into larger and larger bodies, until asteroid size proto-planets — looking much like giant dirty snowballs — begin to form. At this point the gravitational attractions of these proto-planets begin to play a larger role and they begin to grow by gravitational clumping and spot welding.

Eventually the proto-planets accrete into planetesimals. These bodies will continue to grow by meteorite bombardment until the solar system is swept relatively free of debris; at which time the planets will have emerged as free and independent bodies, rotating on their axis and revolving around their central star.

One should note that the above description is only a general explanation for the development of a nebular into a star with a family of planets revolving around it. This description is not meant to be specific for all nebulae, for each nebular follows its own evolutionary course. Double or triple star systems may develop from a nebular cloud. Some nebulae may break up into multiple star systems. Still others may develop into solar systems, which may be composed of many planets or just a few. Finally, some nebulae might even take on complex natures having two or more stars with each star having its own solar system.

The final configuration of a nebular depends on many factors. Two of the more important determinants are its initial mass and its original composition. As noted earlier, this composition is mostly hydrogen and helium with lesser amounts of the other elements.

If the initial mass of the star — its solar mass — is less than about one/third of the mass of the Sun, then it will become a brown dwarf. Brown dwarfs are sub-stellar objects that have a mass just below that which is needed to ignite nuclear fusion reactions within their cores. Their mass range is between that of a large gas planet such as the planet Jupiter and low mass stars.

If the initial mass of the nebular is about one to about five solar masses, then it will go through a similar evolutionary course that the Sun has gone through. After about ten to twelve billion years the hydrogen in its core becomes exhausted, leaving a core of almost pure helium. The core then shrinks while the outer layers expand and the star becomes a red giant.

Eventually the helium in the core fuses into carbon and the outer layers expand into space. What is left is a small, brightly burning star about the size of the earth. Such stars are called white dwarfs. It is theorized that once such stars deplete their helium as a source of nuclear fuel they will burn themselves out, glowing in the infrared for a few millennia before actually dying out.

A star of about ten to twenty solar masses follows a pattern similar to the preceding type of star, but the greater gravitational forces will continue to fuse the carbon into neon, silicon, and the heavier elements up to iron. Since iron is a stable element and it absorbs energy rather than release it, the core will be overcome by its own gravity. It becomes extremely dense and when the pressure builds up high enough it explodes in a supernova. (In 1987, the Southern hemisphere was able to witness a supernova with the explosion of Sanduleak, a hot, blue-white star, similar to Rigel in the constellation Orion. At the time of its explosion, Sanduleak became the brightest star in the Southern sky.)

During the first few seconds of a supernova particles called neutrinos are formed and the protons and electrons in the core form into neutrons, forming a neutron star. An enormous shockwave rips outward and, in a gigantic blast, the neutrinos tear through the surface of the star and carry off most of the energy of the supernova. The explosion heats the outer layers of the star and creates those elements that are heavier than iron. The outer layers of the supernova will continue to expand, becoming the raw material of future nebulae.

The immense gravitational contraction of the neutron star will greatly increase its rotation and intensify its magnetic field. The charged particles surrounding it will emit radiaton and the star itself will emit radio waves in pulses. Such a star is also called a pulsar.

Finally, astronomers believe that a star greater than about twenty-five solar masses will not explode when the core fuses into iron. It is believed that such a star will continue to contract. When its nuclear fuel is exhausted nothing can prevent further collapse. It becomes a black hole, drawing in everything within its event horizon.

However a star or star system may originate or end up, all stars are classified according to their luminosity and spectral class (some astronomers prefer to use absolute magnitude and temperature). This system of classification was introduced by the Danish astronomer Ejnar Hertzsprung (1873 - 1967) and the American astronomer Henry Russell (1877 - 1957).

Giving the Sun a luminosity of positive one, all stars with a greater luminosity are given a multiple of this number, while those with less luminosity are given a percentage of this number. (Those who use absolute magnitude give the Sun a positive five and add to that number for stars that are dimmer than the Sun and subtract from it if the star is brighter than the Sun.)

Thus, a star with a luminosity (absolute magnitude) of one thousand times that of the Sun is given a 1000 (zero). While a star with a luminosity of one hundred thousand times that of the Sun is given a 100,000 (-5). A star with a luminosity of only one/one-hundredth that of the Sun is given a .01 (+10). While one that has a luminosity of only one/ten-thousandth that of the Sun is given a .0001 (+15). A similar ratio is used for comparing a star’s diameter. Again, the Sun is given a figure of positive one to represent its diameter and stars with greater or lesser diameters are given either a multiple or percentage of this number.

The spectral classification of a star depends on its temperature. Each different class is given a different letter of the alphabet. The classification for most stars starts at the hot, blue stars, designated with the letter O, and proceeds with decreasing temperature to the relatively cool, red burning stars, designated with the letter M. The stars that fall between these two extremes are designated either B, A, F, G, or K. This is going from the hotter stars to the cooler burning stars, respectively. The Sun is considered to have a spectral classification of G and is a yellow star.

By graphing luminosity and spectral class (absolute magnitude and temperature) one obtains a systematic grouping of most of the stars in the universe. These are a band of stars running diagonally in a rather stretched out “S-shape” pattern (similar to the human spinal column as seen from the side) from the hot, blue stars to the lower temperature, red burning stars of the Hertzsprung-Russell diagram. These stars have come to be known as the main sequence stars and they are by far the largest group of stars presently known in the universe.

However there are two other groups of stars. First are the giants and the super-giants. These stars have a high luminosity, but their spectral class indicates that many of them are relatively cool burning stars. Second, there are the dwarf stars mentioned earlier. One may thus see that a star’s position on the spectrum-luminosity diagram reveals quite a lot of information about the star. One may learn its size, its temperature, its color, its spectral class, its absolute magnitude or its luminosity. But most important, by studying a stars position on the H-R diagram — as many astronomers commonly call it — one may learn whether or not any particular star is a main sequence star.

Because most main sequence stars follow a similar evolutionary course to that followed by the Sun, this in turn will help one to learn something about a particular star’s history, whether it may or may not have planets revolving around it and something of its possible future.

As mentioned earlier, each nebular follows its own evolutionary course. Since the dawn of time mankind has searched to discover the events that took place in the evolution of the Sun and solar system. In order to obtain an understanding of this evolution modern scientists have gathered information from a wide range of sources. Today one may obtain this information by reading almost any astronomy or geology book.

The information that has been gathered by the scientists suggests that the Sun, the planets and their satellites and the other celestial phenomena of this solar system formed about 4.6 billion years ago after what is considered a normal developmental history.

After the newborn Sun ignited its nuclear furnace, the solar wind cleared the solar system of most of the enveloping cloud of gas, dust and ice crystals. However, enough debris still exists to cause an occasional meteor to enter the earth’s atmosphere or even to strike the earth (or another planet or satellite) as a meteorite.

The new solar system that emerged from this envelope was described by Nicolaus Copernicus (1473 - 1543) in the book De Revolutionibus as a uniform, regulated system. The ordered symmetry of the planetary system and their elliptical, although nearly circular, orbits, as described by Johannes Kepler (1571 - 1630), assures one of the common origin of these and all other celestial phenomena revolving around the Sun. However, there are a few peculiarities and paradoxes of this solar system that needs to be explained.

One example is the composition of the planets. The terrestrial planets — Mercury, Venus, Earth, and Mars — are all dense, metal rich and relatively small. However the giant planets — Jupiter, Saturn, Uranus, and Neptune — are all large and enshrouded by the volatile elements. (The anomalously small Pluto and its satellite Charon, although resembling the inner planets, are now grouped with the dwarf planets: Ceres, Eris, Haumea and Makemake.) The different chemical compositions of the planets are explained by something the scientists call the condensation sequence.

After a first generation star explodes, the scattered debris randomly accumulates into large clouds of matter. At first, these interstellar clouds are very hot but they rapidly cool off as they form into new nebulae. Chemical studies have shown that as a nebular forms the various elements and compounds in it will condense out at different temperatures. These studies have further shown that the refractory elements are the first to condense while the nebular is still very hot. The silicates and ferro-silicates are the next to condense out. Finally, water ice, ammonia, methane and other volatile elements will appear.

Since the inner part of the nebular will be hotter than the outer areas, it follows that the inner planets will have a lesser amount of those elements and compounds that condense out at the lower temperatures. The inner planets will be composed of mostly rocks and metals. While the outer planets will be built up with the more abundant ices, along with rocky materials and metals.

Another reason that the inner planets of this solar system have a different chemical composition than the outer planets is because the outer areas of the disk in which the giant planets formed were shaded by the inner parts of the disk. This, plus their greater distances from the Sun, caused the outer planets to receive much less solar radiation while they were forming in the disk. They were thus kept at a cooler temperature and retained more of the volatile elements than the terrestrial planets and have a different chemical composition than them.

Another problem of the solar system that has plagued the scientists for a long time is the Sun’s spin on its axis. According to the principle of the conservation of angular momentum, the Sun should be rotating on its axis much faster than it is in fact rotating. However, astronomers now understand that the Sun shot out ionized particles at a much higher rate several billion years ago than it does today. Since ions must travel in a magnetic field, the strong magnetic field of the rotating Sun would have pulled the ions in the disk along with itself as it rotated on its axis.

If one can imagine how a spiral galaxy looks from above, with arms of stars swirling out from the center in a circular pattern, such would be a fairly accurate picture of what the ionized particles held in the magnetic bands of the Sun’s disk looked like.

These bands of ionized particles in the slowly rotating disk would have exerted a dragging effect on the rapidly rotating Sun and would thus have applied a breaking effect on the Sun, slowing down its rotation. Thus, the angular momentum of the Sun was lost to the slowly rotating disk.

Still, another paradox of the solar system consists mainly with the outer planets. With their rings and their own satellites revolving around them, they all resemble miniature solar systems. Consequently, astronomers believe that this dictates that they evolved in a similar process to the Sun, although on a much smaller scale.

Each planet formed where an eddy developed in the revolving disk. The outer planets, being more massive, swept up more debris of the disk, which further increased their masses. Mini-disks formed around each one of them in a manner similar to the disk that formed around the developing Sun. The satellites of each planet accreted from the disk surrounding each planet.

Jupiter formed at an area of the disk that was closer to the Sun than the other giant planets. Having a shorter orbital period, it was thus able to sweep up more material. That is why Jupiter is so massive and has such a strong gravitational field. It has a gravitational field strong enough to compete with the Sun’s gravitational field, which prevented the asteroids from forming into a planet. Scientists have calculated that if Jupiter were just a little more massive it would have developed into a star and the Sun would have been a binary system.

Which brings one to the planet earth and its origin. The scientists assume that the earth formed, as did the other planets of this solar system, where an eddy formed in the disk of the evolving solar system. Within these eddies small pockets of solid matter accumulated in the rings revolving around the Sun. These pockets gradually grew by aggregation of smaller bodies into larger ones. This continued until the snowball-like planetesimals were large enough to grow by gravitational accumulation.

The separation of the earth into core, mantle, and crust happened while the planet was still in the process of forming. Each time the embryo earth was struck by an asteroid the two shattered themselves. Then the remnants of the two bodies would aggregate into a larger body. When the new, larger proto-earth cooled off the heavier elements would have collected near the center and the lighter elements would have collected near the surface.

Eventually, after many millennia, the solar system was cleared of enough debris that bombardment of the earth — and other planets — by asteroids and meteorites slowed enough to allow the earth’s crust to solidify over the molten outer core and solid inner core, which helps produce the earth’s magnetic field. After the earth’s crust solidified oceans of liquid water began to build up on the earth.

However, there exists a peculiarity of the earth that is not so easily explained and that is the moon. Any discussion on the origin of the earth must also include an explanation on the origin of the moon. There are several reasons for this. The most important being that the moon is not merely a simple satellite of the earth, as are the satellites of the outer planets.

(One should note that many astronomers believe that the two small moons of Mars — the only other inner planet to have natural satellites — were asteroids that were captured by that planet while the solar system was forming.)

It is more correct to say that there is an earth/moon system revolving around the Sun. That is to say, the moon does not revolve around the center of the earth, which revolves around the Sun, as do all the satellites of the giant planets. The earth and moon revolve around a common center of balance that is just a few kilometers below the surface of the earth; it is this center which revolves around the sun. This indicates that their evolutionary histories are probably intricately interwoven. There are other facts that also indicate this.

For example, the side of the moon that is facing the earth has a thinner crust than the opposite side of the moon but the earth has a relatively uniform crust. The side of the moon facing the earth has more “seas” or dark areas than the opposite side. (One should note that the seas are vast lava flows that leaked out onto the surface of the moon millions of years ago.) The geologically inactive moon compared with the geologically active earth. The apparently nonmetallic core of the moon contrasted with the earth’s iron and nickel core.

The moon has less differentiation than the earth. The moon is the largest satellite relative to the planet it revolves around than any satellite of this solar system. There are other oddities of the earth and moon and they all indicate that there is something very peculiar in the evolutionary histories of the earth and moon.

It has been proposed that late in the earth’s formation it was struck by an extremely large asteroid. Some believe that it could have been about ½ the size of earth or as large as the planet Mars and have named the asteroid Orpheus. Others have named it Theia.

This collision caused the core of the impactor to fuse with the earth’s core and threw trillions of tons of rock and debris from the earth’s crust and mantel into orbit around the earth. A ring, similar to the rings around the four giant planets, soon formed around the primitive earth. This ring of debris then aggregated into the moon as one knows it today. Thus, much of the moon is composed of material that was at one time part of the earth’s crust and mantle.

This “giant impact theory,” as some scientists have called, was proposed in the mid 1970s by two scientists, Dr. William K. Hartman and Dr. Donald R. Davis. According to their theory, an impact by a large asteroid in the latter stages of earth’s formation could account for an iron-depleted moon as well as the masses and angular momentum of the earth-moon system.

Lunar samples returned by the Apollo astronauts manifest that the moon and the earth have similar quantities of oxygen isotopes. But the moon has far less volatile material than does the earth’s crust. However, heat generated by the impact would have vaporized all the volatile material that was thrown into orbit. It would then have been lost to space.

The earth has an iron and nickel core. The moon lacks metallic iron in its core because the core of the asteroid stuck to the earth. Thus the moon formed from the silicate material of both bodies; the debris that was flung into orbit around the earth by the collision.

This hypothesis helps to explain the two different faces of the moon. It helps to explain why the side of the moon facing the earth has more “seas” than the opposite side; it was probably struck more often by the flung off debris than the far side of the moon.

But most important, the collision theory explains why the moon is so dry — all, or nearly all, of the volatile material evaporated in the heat of the impact — and it explains the angular momentum of the earth/moon system. The asteroid probably struck the earth a glancing blow or just off center which would have altered the earth’s rotational speed.

Finally, one should note that this explanation for the origin of the earth/moon system is only a working hypothesis. Although it is not the only hypothesis, it appears to be better at explaining most of the paradoxes of the earth/moon system than other hypothesis.

One can only wait for further research by the scientists in order to answer the question on the origin of the earth and moon system. However, one can get a better understanding of this hypothesis in an article in the July 1994 issue of Scientific American titled The Scientific Legacy of Apollo by G. Jeffrey Taylor.

Alpha Omega

Star World