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Excerpts from my book,
"History of the Triple Existence"
by William McGaughey
FROM THE INTRODUCTION
This book, History of the Triple Existence, narrates the creation of the universe and everything in it. A work in the field of big history, it is 560 pages long.
One might ask: What is the “triple existence”? We can approach the subject experientially. I would ask you to close your eyes for a moment. Now open them. What do you see? If you are sitting indoors, you will likely see objects embodying the triple existence.
This phrase, “triple existence” refers to a world - our world - made of three types of being: matter, life, and thought. Sometimes their objects are in a pure form. Sometimes they are mixed.
Suppose you are looking at a table made of wood. This table consists of matter; it is a physical object comprised of atoms and molecules. However, the table also represents a product of life. Wood is produced in trees. Each tree represents a species of life belonging to the plant kingdom. Finally, the table also incorporates thought, since a furniture maker created it according to a thoughtful design. So we have a three-in- one kind of existence embodied in an object appearing before your eyes. Look around the room and find other objects of this sort.
If you go outside, you are apt to find matter unmixed with life or human thought. The rock in a mountain cliff, the sand on a beach, the water in an ocean or lake, the clouds floating in the air, and the stars twinkling in the nighttime sky are examples of pure matter. Outdoors, you may also see grasses and trees, flowers, dogs, insects, and other human beings. These things illustrate life. The concrete highways, metal railings, and brick walls are matter combined with human thought.
You get the idea. Our world is a single place but, if you look for it, you will find three different kinds of being.
The material universe had a beginning and so did life and thought. Each type of being has its own creation story. The purpose of History of the Triple Existence is to tell the three stories in a seamless narrative. We do this in 560 pages of a book.
The goal is to cover everything in a short space. Obviously, we cannot go into much detail. For example, a wooden table, too, has a creation story. It might involve the history of furniture making, of this particular type of table, of the company that made the table, and even of the particular craftsman or factory worker who was involved in its production. Few people would be interested in a “history of everything ” down to this level of detail . So what do we do to be representative of the whole?
History of the Triple Existence, like other works of big history, tells the story of creation in separate chapters that cover the different types of being. Matter began with the Big Bang. Life began with single-celled organisms that arose from inanimate matter. Thought began with human culture, especially in civilized societies that acquired the art of writing.
The Big Bang is believed to have happened 13.8 billion years ago. Life as we know it occurs exclusively on planet earth. The earth was formed 4.56 billion years ago. Life first appeared around 3.5 billion years ago. Eukaryotic cells, supporting the more advanced forms of life, appeared 2.1 billion years ago. The human species appeared between 100 ,000 and 200 ,000 years ago. The first civilizations appeared in Egypt and Iraq between 5,000 and 6,000 years ago. So we see that there is a great disparity in the times when the different types of being appeared.
Now, let’s get started with the story.
FROM THE FIRST CHAPTER
THE BIG BANG AND QUARKS
In the beginning, there was nothing. The entire universe shot out of a very small space 13.8 billion years ago in an event known as the “Big Bang”. A primordial explosion of immense proportions occurred as particles of incipient matter and energy shot away from each other at an incredible speed. It is hard to imagine what exploded. There were then no atoms. There were no galaxies or stars. The ejected substance was not matter but an amorphous plasma filled with elemental particles called “quarks”. Physicist Murray Gell-Mann named them after an undefined word in James Joyce’s novel Finnegan’s Wake.
Quarks are building blocks of the atomic nucleus. Understood in terms of quantum mechanics, they are subatomic force-carrying particles that vibrate in waves having numerically discrete units of “spin”. The spin tells what a particle will look like from various directions as it rotates. One type of quark, having a spin of 0, looks the same in all directions. A quark with a spin of 1 changes appearance in the middle of a rotation except that it returns to its original appearance after a full rotation. A quark with a spin of 2 looks the same after a half (180 degree) rotation. Particles having a spin of 1/2 come back to the same appearance after two rotations. They make up all the matter in the universe. Those with spins of 0, 1, and 2 create forces between particles.
Apart from spin, there are several different types of quarks differentiated by “flavor”: “up”, “down”, “strange”, “charmed”, “bottom”, and“top”. Each flavor also has three colors: “red”, “green”, and “blue”. Protons and neutrons are each made of three quarks. A proton has two “up” quarks and one “down” quark. A neutron, on the other hand, has two “down” quarks and one “up”. These are the most stable combinations although other types of quarks can be assembled in unstable structures of greater mass.
The 1/2 spin particles comprising matter are subject to the “exclusion principle” discovered by Austrian physicist Wolfgang Pauli. This principle states that two similar particles cannot exist in the same state; they cannot have both the same position and the same velocity. In practical terms, it means that matter has exclusionary boundaries. The particles cannot collapse into a state of infinite density. The same is not true of force-carrying particles. They are not subject to the exclusion principle and therefore can accumulate in very large quantities of energy.
Physicists put the force-carrying particles in four categories, some- times called the “four forces”. Gravity, the weakest force, exerts an attraction between masses of material, even at a distance. Electromagnetism consists of electrically charged particles that either attract or repel each other. Two positively charged particles repel each other, as do two negatively charged particles. However, negatively and positively charged particles attract each other. This force is what binds protons and electrons together in atoms. The “strong attraction” force holds quarks together in protons and neutrons. It holds the atomic nucleus together. The “weak attraction” force is seen in radioactive decay.
Gravity is weaker than the other kinds of forces but it has a significant impact on the universe because it involves objects of large mass interacting with each other at great distances. For example, the force of gravity holds the earth in a stable orbit around the sun. It is believed that the sun and earth exchange particles with a spin of 2 known as “gravitons” to exert the gravitational force.
The electromagnetic force is trillions of times stronger than gravity but it is only effective on a small scale. This is the force that holds negatively charged electrons in an atomic structure along with the positively charged protons. It does not interact with gravitons. This force always involves a polarity of charges. The attractive or repulsive force is exerted by the exchange of “photons” which are massless particles with a spin of 1.
The strong nuclear force is what holds quarks together in protons and neutrons and also what holds protons and neutrons together in an atomic nucleus. This is carried in a particle with a spin of 1 called a“gluon”. The strong nuclear force has a property called “containment” which puts particles into a structure having no color. For example, a “red” quark combined with a “green” and a “blue” color held together by gluons would produce “white”, a colorless condition. At normal energy levels, the strong nuclear force holds quarks tightly together. They tend to come apart at higher energy levels.
The weak nuclear force, responsible for radioactivity, affects matter but not particles with spins of 0, 1, and 2 such as photons and gravitons. Besides photons, this force is carried by three other spin-1 particles known as “massive vector bosons” - W +, W-, and Z0. At high energy levels, these particles show similar behavior. At low energy levels, however, they behave in many different ways, despite being the same type of particle.
All these particles are smaller than the shortest wave length in the electromagnetic spectrum and are therefore unable to be seen. They are difficult for laymen to understand. Subatomic particles can be observed when particle accelerators, generating strong electromagnetic fields, accelerate particles that are concentrated in beams and then smash them into each other, causing disintegration of their component parts. It is normally the effect of the collisions that can be observed.
Modern physics is built upon a foundation of mathematical equations supported by experimentation with specialized equipment. Often the theory comes first and is followed by the confirming experiment. For example, the Higgs boson, which allows particles to assume mass, was predicted in the 1960s but only recently verified.
EVENTS OF THE FIRST THREE MINUTES
At any rate, the cosmic soup originally consisted of these rather mysterious particles called “quarks”. Realize that, at the beginning of existence, matter had not yet separated from energy. Neither truly existed. In the first split second of creation we had only the subatomic particles. The primordial plasma was heated to a temperature of more than one trillion degrees Celsius. What came next is truly remarkable. The universe began to expand. It expanded rapidly in an unbelievably short period of time. This was the Big Bang.
It is believed that within 10-43 seconds, gravity emerged as a separate force. (This is one ten millionth of a trillionth of a trillionth of a trillionth of a second.) The gravitational particles appeared. Around 10-34 seconds into the creation, matter appeared in the form of quarks and electrons. Anti-matter simultaneously appeared. The “strong force” split from the “electro-weak” force, releasing a large amount of energy. Then, around 10 -10 seconds after the Big Bang, there was a split between the “electromagnetic force” and the “weak force”. There were now four forces: gravity, the strong force, the weak force, and the electromagnetic force.
But there was more to do. Around 10-5 seconds after the beginning, quarks combined to form protons and neutrons. Anti-quarks, their counterparts in anti-matter, formed anti-protons, which are protons having a negative charge. The protons and anti-protons collided. As their respective masses were extinguished, photons of energy were released. However, there were slightly more protons than anti-protons - perhaps one part in a billion more. That meant that after the mutual annihilation, some protons remained. It was those protons that make up the nuclei of matter in our universe.A similar process took place with respect to electrons and positrons, which are electrons with a positive charge. These particles also collided and annihilated each other. As in the case with protons, there were slightly more electrons than positrons so that only electrons existed after the mutual annihilation. At the end of the process, after the particles of opposite charge were paired off and annihilated, only protons, electrons, neutrons, and photons of energy remained.
All this happened within a very short time. Around three minutes after the Big Bang, most of the surviving quarks had taken the form of protons and neutrons in hydrogen or helium nuclei.
The next phase of activity took place in the next 380,000 years. This is the third part of our story. Here we see the formation of atoms as negatively charged electrons become paired with positively charged protons. The fourth part of the story of cosmic creation is what has happened in the remaining 13.7 billion or more years.
The word “story” is applied loosely to this situation. Stories describe events that take place in time and space often involving human beings. There were, of course, no humans when the universe was created. Space and time did not exist in a recognizable form. Therefore, there was no “place” for events to occur.
If there were events in the story, they would have had to involve objects moving about in space. Two types of being filled this early universe: energy and matter. Matter we see as something that fills space. It has spatial boundaries marking its territory. Energy, in contrast, would be what allows matter to move from one place to another. Energy and matter would jointly create a particular set of events.
At this point, however, the universe was contained in an infinitesimal volume of space. Energy and matter were fused in a plasmic mass. The physics of Albert Einstein holds that matter is convertible into energy, and vice versa, according to the formula e = mc².
Einstein’s theory of relativity contemplates that both time and space can be bent. Space bends around large structures of matter that exert gravity. The perception of time changes with an observer’s motion. In short, the traditional framework of storytelling breaks down under extreme conditions.We tend to think of space as a realm of limitless expanse. But space does not exist without matter. Modern physics regards space as a medium that expands with content. The general theory of relativity holds that gravity represents space being bent in the presence of matter.
Physicists like to say that “matter tells space how to bend and space tells matter how to move.” According to this view, matter would not be “exploding out into space” after the Big Bang but moving apart from other matter with the expansion of space. In that period, space would be inflating like a balloon so that its volume would be proportionate to the matter contained.
THE AGE OF RADIATION
Einstein’s physics is relevant to events happening at the start of creation. We did not have objects moving about in space in orderly ways as Isaac Newton’s equations prescribe. Instead, the raw elements of the physical universe were colliding with each other. Energy was embodied in photons vibrating at certain frequencies and wave lengths that traveled at the speed of light. Matter was embodied in neutrons, protons and electrons. Meanwhile, the universe was rapidly expanding.
A proton is positively charged. A neutron has no electromagnetic charge because each neutron contains a positively charged proton and a negatively charged electron that offset each other. Protons and neutrons form the nucleus of an atom, which is positively charged. Negatively charged electrons surround them in the same number as the protons, making the atom neutral in its electromagnetic charge. The simplest and most plentiful element, hydrogen, contains a single proton and a single electron.
Energy is a bit harder to explain. We think of this as motion, heat, or light, but energy is also associated with massless particles called “pho- tons” having a spin of 1. These photons vibrate at certain frequencies and travel through space in waves of particular length. Greater frequency of vibration is associated with more heat. The primordial plasma was once very hot but it has cooled considerably as the universe expanded.
At the time of the Big Bang, the universe was an amalgam of energy and matter compressed into a very small space. For thousands of years, photons spontaneously changed into matter. Matter freely changed back into photons. Matter and energy were mixed together in the primordial soup. Einstein’s equation describes the quantitative relationshipbetween matter and energy as they become converted into each other. This process of conversion has been compared to steam condensing into water and water freezing to become ice.
As the universe expanded, the wave length of the photons increased so that a cooling process took place. The radiation could then not so easily be converted into matter. Energy converted into matter made equal quantities of protons and neutrons along with free electrons. Neutrons each have a proton and electron. However, free-standing neutrons are unstable; they have a half-life of 887.5 seconds. Many broke down into protons and electrons.
Some neutrons survived in combination with protons. A single proton and neutron fused together forms deuterium (²H), which is the nucleus of a heavy-hydrogen atom. Several deuterium nuclei collided with free-floating protons to produce helium nuclei (consisting of two protons plus one or two neutrons). In a few cases, helium nuclei collided with protons to produce nuclei of lithium (three protons plus three or four neutrons) which were unstable.
The nuclei of deuterium atoms started to form when the temperature had dropped to around 3 billion degrees Celsius but they were soon knocked apart in particle collisions. By then, the proportion of neutrons had dropped to around 14 percent of all matter. When the temperature had dropped to 1 billion degrees, the radiation was insufficient to destroy the deuterium nuclei. In the next few seconds, most of the remaining neutrons were combined with protons to produce nuclei of helium-4, each consisting of two protons and two neutrons. Helium-4 nuclei are stable.
Afterwards, the nuclei of hydrogen, helium, and, in a few cases, lithium combined with free-floating electrons to form electrically neutral atoms. These became the elemental building blocks of matter. But there was a catch. Each time an atom was created, a photon of energy was released. The surplus photons collided with electrons that had not been captured in atoms. The two types of energy particles, mixed together, moved at the same temperature in mutual interference.
A kind of stalemate ensued. The free-floating photons collided with atoms, knocking out their electrons which became free once again. The positively-charged nuclei of these atoms then picked up other electrons. With the recombination of atoms, photons were again released. They then reacted with other electrically neutral atoms, perpetuating the cycle.
And so it went for the first 380,000 years. The photons of energy andelectrons of mass interfered with each other’s development. This was because the universe was still hot. It consisted of white-hot particles of matter in a sea of photons. Energy and matter could not escape each other’s clutches.
After around 380,000 years, however, the universe had expanded to the point that its temperature dropped to below 3,000 degrees Kelvin. The increased wave length of the photons generated insufficient energy to ionize the hydrogen atoms. Those atoms remained intact. Matter and energy went their separate ways.
What happened then was that the previously formed nuclei combined with electrons to create atoms. The electrons, now locked in atoms, could no longer interfere with the photons of light so that the latter could now travel unimpeded through space. The electrically neutral atoms, which balanced the positively and negatively charged particles, no longer blocked the transmission of light. The photons were then able to move through a clear universe.
That is why astronomers can detect radiation emitted after universe had cooled to a sufficient point (3000 degrees Kelvin) but no earlier: Light was not then able to escape. This energy exists today in the form of cosmic background radiation. The level of radiation, while slowly decreasing, is much the same no matter where one looks in the night sky. Its temperature is around 2.7 degrees above absolute zero.
Prior to their separation, the mass density of energy exceeded that of matter. The universe was dominated by the dynamics of energy. Subsequently, it has been dominated by matter. Matter exists mostly in the form of hydrogen atoms. Helium accounts for about 25 percent of its mass. Atoms of these two elements, along with energy waves, floated out through space as the universe expanded.
The story now enters the realm of chemistry. The atoms of matter are chemical elements arranged in the periodic table. Each element has a certain number of protons in the nucleus surrounded by an equal number of negatively charged electrons. Except for hydrogen, each element also contains one or more neutrons in its nucleus which help to hold the protons together. When two or more atoms share electrons, they form chemical compounds. The valence of an element tells how many electrons can be shared by each atom. Molecules are formed as a result.In 1869, a professor of chemistry, Dimitri Mendeleev, presented his theory of the periodic table to the Russian Chemical Society, which placed all known elements in a tabular chart with recurring properties. This scheme now accounts for 118 known elements, most occurring naturally.
Elements in a group (in a vertical column in the periodic table) have similar chemical or physical characteristics. The lighter elements, with fewer protons and electrons, are more prevalent in nature. Heavier elements such as uranium tend to break down through radioactive decay. Hydrogen, the lightest element, is also nature’s most common.
Hydrogen atoms consist of one positively charged proton and one negatively charged electron. Helium atoms consist of two protons, two electrons, and one or two neutrons. There are also rarer isotopes of these elements such as deuterium.
Only hydrogen and helium (and a smattering of lithium) existed in the aftermath of the Big Bang. All other elements in the universe were subsequently created within stars or in human laboratories.
Even though atoms are larger than subatomic particles, they are still very small. Most of their mass is contained in the nucleus. Electrons, with a much smaller mass, orbit the nucleus like a planet. The diameter of atoms is around one ten-millionth of a centimeter. Even so, they occupy space. Matter has a particular location in space that excludes other matter. And since atoms are so small and the universe is so large, there must be an unbelievable number of them out there.
Now we come to the final 13.7 billion years of our story. At this point, the universe is expanding. Hydrogen and helium atoms have become dispersed in space. If these atoms had been evenly distributed throughout the expanding universe, not much more might have happened; for an uneven density of matter is required for gravity to take effect. Fortunately, some of the free-floating atoms came to be clustered in space.
There are several theories about this. Some scientists believe that the materials blasted into space after the Big Bang may have been arranged in networks whose strands intersected in particular places. The uneven distribution of atoms may also have been due to pressure changes or “sound waves” set off by minor disturbances of particles during the earliest period. Even if the universe does not presently reveal such waves, they have left fossil patterns in the hot and cold spots of greater or lesser density. Electromagnetic forces in the universe may also have caused an uneven distribution of the matter floating in space.
Electromagnetic, strong nuclear, and weak nuclear forces originally produced the atoms. Now the neutrally charged atoms situated in places of unusual density became subject to the weaker but still potent influence of gravity. Gravity is a force by which matter is attracted to other matter by their respective masses. According to Newton, its force is proportionate to the square of the mass of two objects and inversely proportionate to the square of the distance between them. There was, then, a gravitational attraction between the free-floating atoms that caused them to move toward each other and become concentrated in a single mass.
In such a way, atoms situated in places of greater density were drawn into clusters by the force of gravity. Large clusters of atoms have more gravity than small ones. Over time, more of the materials in the universe were therefore gathered in clusters of increasing size. The atoms drawn closer together formed clouds of more tightly compacted materials. At close distances, the gravitational attraction greatly increased. The atoms - mostly hydrogen molecules - became even more strongly attracted to each other within the cosmic clouds.
Within a large cloud, there was enough gravity in certain places that the atoms collapsed upon one another. This happened at an accelerating speed forming a core of extremely dense materials. Next, the gravity produced by this event attracted other atoms from the cloud. Their additional material rained down upon the core further increasing its mass.
The kinetic energy of new materials collapsing upon the core produced increasing heat. The mass of materials began to rotate. Stellar winds blew some of this material out along a disk on a plane perpendicular to the axis of rotation. As the collapsed mass acquired still more material, the compacted atoms at the core became heated to the point that hydrogen atoms fused to produce helium. This thermonuclear reaction produced radiating energy that pushed outward to prevent further collapse. A new star was born.
Stars come in many sizes, temperatures, luminosities, ages, locations, and chemical compositions. The best-known star is, of course, our own sun. The sun is a “normal star”, emitting radiation from nuclear reactions at its core. The outward pressure from those reactions balances the inward pull of gravity. The sun is about 4.6 billion years old and has a life expectancy of 10 billion years. It is therefore younger than manyother stars in the 13.8-billion-year-old universe.
An important characteristic is the star’s mass. This depends on how much material was taken from the interstellar cloud that collapsed. Stars whose mass falls within the range of between one fifteenth and one hundred times the sun’s mass are able to sustain themselves for long periods of time by nuclear reactions converting hydrogen atoms into helium. Stars larger than this are unstable; they tend to blow off the excess material. Stars below the lower limit have insufficient density and temperature to sustain a nuclear reaction.
The size of a star determines its fate. Generally speaking, the larger the star, the more densely compacted are its atomic materials and the more heat will be produced. Although larger, its fuel will burn much more quickly so that the life span of the star is shorter. A medium-sized star such as the sun will last for 10 billion years. Stars ten times the size of the sun may last only 30 million years. On the other hand, some gaseous bodies such as the planet Jupiter are too small to sustain a thermonuclear reaction; they will last indefinitely.
Astronomers looking at the night skies see an almost limitless number of stars. There are various ways to classify them. A common catalog lists stars from the hottest to the coolest spectral types: O, B, A, F, G, M. Giant and supergiant stars belong to the R, N, and S types. To determine the type, astronomers want to know where a star is in its life cycle, principally with respect to converting one atomic element into another.
Often the radiation detected by astronomers is mixed in several different types. If the light from a star is passed through a spectrometer, its rays will separate by frequency of vibration. Gamma rays, the most energetic type of radiation, have the shortest wave lengths and highest frequencies. Next come X-rays with slightly longer wave lengths and lower frequencies; and beyond that, rays of ultraviolet light. Moving toward the longer energy waves, we have the frequencies of visible light, ranging from violet to indigo, blue, green, yellow, orange, and red, as the wave lengths increase and frequencies decrease. Below the red spectrum of visible light are infrared light and, finally, radio waves. Those have the longest wave lengths and lowest frequencies of vibration.
Spectral analysis tells astronomers which elements arefound in a star and what type of star it is. It gives information about a star’s temperature, chemical composition, and brightness. The hotter stars tend toward the blue end of the spectrum; the cooler ones, toward the red. Also, there may be bands in the spectrum of frequencies that are dark, indicating that light has passed through certain materials in space. We call these “absorption lines”. Certain chemical elements absorb certain frequencies of light. That tells astronomers which elements are present in space.
Astronomers plot the luminosity of stars against their color (indicating surface temperature) in a scheme known as a Hertzsprung-Russell diagram. Most stars lie in a narrow band where luminosity (brightness) and temperature are directly correlated. Stars with cooler surface temperatures are generally less luminous than those with higher temperatures. There is a downward-sloping cluster of stars in this diagram called the “main sequence” that fits this pattern. It includes stars like the sun that are still converting hydrogen into helium. Most stars are or have been in the main sequence.
The significance from a Big History standpoint is that stars within a certain range of mass experience life cycles. The universe has a history. While converting hydrogen to helium and emitting energy, these stars exhibit a fixed ratio between temperature and luminosity. They are to varying degrees both hot and bright depending upon their mass. Red giants, which have exhausted their thermonuclear fuel, expand to a much greater size where they become bright (to earthly observers) but are relatively cool. So they deviate from the main-sequence ratio.
After its energy is exhausted, such a star then contracts by force of gravity until it becomes a white dwarf. The contraction produces heat. White dwarfs depart from the main sequence in having low luminosity but being relatively hot. Departure from the main sequence indicates the approaching end of a star’s existence as a generator of energy. Black dwarfs, compacted bodies that emit no energy, represent the end of the line. They are dead.
The conversion of elements within main-sequence stars produces immense interior temperatures. The high temperatures cause particles of matter to be disintegrated and recombined. The sun has a temperature of 15 million degrees Kelvin (above absolute zero) at its core, where the recombination takes place, and 5,700 degrees Kelvin on the surface. That is a significant difference. The interior heat radiates outward from the core first in the form of gamma rays and then in less energetic waves of heat or light as it works its way through the sun’s mass. Finally, the radiating heat is dissipated by convection of gases to produce the lower surface temperatures. This outward thrust creates pressure offsetting gravity so that the sun does not collapse. The energy then radiates into space.
The extreme heat at the core of a star can fuse hydrogen atoms. This process is called the “p-p (proton- proton) chain". Two loose protons from ionized hydrogen are fused to create the nucleus of a deuterium (heavy hydrogen) atom which contains a proton and a neutron in weak combination. A positive electron (positron) and a particle called an antineutrino (the antiparticle associated with neutrinos) are released in the process. The positrons combine with the negatively charged electrons to annihilate each other. Each such annihilation produces 1.02 megaelectron volts of energy.
Deuterium is unstable. A stray proton may then be fused with its nucleus to produce an isotope of helium known as helium-3, having two protons and a neutron. A “hard” (higher energy) X-ray and a gamma-ray are also emitted. Next, at higher temperatures, two nuclei of helium-3 fuse to create helium-4. Its nucleus contains two protons and two neutrons. The two unneeded protons from the helium-3 fusion are then released.
Helium-4 is a stable helium atom. Its creation by fusing hydrogen nuclei leaves a mass slightly less than the mass of the original four hydrogen atoms. Approximately 0.833 percent of the mass was lost as energy was released during the creation of the deuterium atoms. This is a large amount of energy.
Since the conversion takes place within the innermost ten percent of the sun’s mass, scientists cannot observe the process directly. Seeing only what leaves the surface of the sun, they must guess what happened inside. Particular attention is given to the production of neutrinos and antineutrinos in the sun’s interior. The antineutrinos involved in producing helium are extremely weak. No instrument can detect them. However, neutrinos involved in the production of anotherelement, beryllium, have more energy and can be detected.
A nucleus of helium-3, having two protons and a neutron, combines with a nucleus of helium-4, having two protons and two neutrons, to produce beryllium-7, which has four protons and three neutrons. If another proton is added to beryllium-7, it produces the nucleus of boron-8 which breaks down into beryllium-8, while emitting a high-energy neutrino and a positron. This type of neutrino is visible in chlorine detectors. Finally, beryllium-8, an unstable isotope, divides into two nuclei of helium-4.
The bottom line is that hydrogen atoms compressed and heated in the sun’s interior are converted into atoms of helium while releasing enormous amounts of energy. The sun needs to convert 674 tons of hydrogen into helium each second to maintain its energy emission. Even though a great amount of energy is produced, there is enough hydrogen in the sun that its thermonuclear reactions can continue for many more years. The sun, which is 4.6 billion years old, has another 5.4 billion years to go before it runs out of hydrogen and the reactions stop.
Stars at least one and a half times the mass of the sun also burn hydrogen but they follow a different course of events. The temperature is so great in their interior that they produce heavier elements such as carbon, nitrogen, and oxygen. It happens in this manner: First a nucleus of carbon is produced. That nucleus combines with a proton to produce a nucleus of nitrogen-13, emitting a gamma ray. The unstable nitrogen nucleus emits a positron which is annihilated when fused with an electron. A neutron is released. The resulting carbon-13 nucleus may then attract another proton to form a nucleus of nitrogen-14, while emitting another photon.
Although the nitrogen-14 nucleus is stable, it may acquire another proton to form oxygen-15, which is unstable. The nitrogen-14 nucleus emits a neutrino and also a positron which is annihilated when combined with an electron, also producing energy. A nitrogen-15 nucleus then remains. This may, in turn, attract another proton to produce a nucleus of oxygen. More likely, however, it will break down into stable nuclei of carbon and helium, releasing a gamma ray. The result of this sequence of reactions is that the original nucleus of carbon is restored along with another helium nucleus.
What happens when the hydrogen fuel of a main-sequence star is exhausted? The hot core comprising 10 percent of the mass, which is comprised of helium, then becomes thermally differentiated from the star’s exterior regions that are too cold to sustain nuclear fusion. When around 12 percent of its mass has been converted to helium, the interior of the star starts to collapse, producing heat. Meanwhile the outer layers comprised of inert hydrogen atoms expand. The interior heats up as the helium, no longer emitting energy, becomes more tightly compacted. Thermal convection from the reheated core, in turn, heats the surrounding layers of hydrogen gas causing the star to expand further. With less density, the star now has a much larger volume than before. Its surface becomes larger and more luminous.
Eventually a new type of star is created whose radius is thousands of times greater than that of the original star. It turns into a red sub-giant star. When the core heats the surrounding hydrogen atoms to 10 million degrees or more, a process of conversion to helium takes place in layers surrounding the core. There is then an additional release of energy which causes the star to expand further. It becomes a red giant. Red-giant stars depart from the “main sequence” group in the Hertzsprung-Russell diagram. They become very bright stars with relatively low surface temperatures. The “turnoff point”, at which main-sequence stars become red giants, depends partly on the star’s chemical composition.
As red giants form, a process called “electron degeneracy” takes place in the heated interior of the star. The electrons cannot find atomic mates in the superheated plasma so they remain at a higher energy level while circulating aimlessly within the plasma. These compressed electrons now supply the main force counteracting gravity. Because the free-floating electrons conduct energy easily in red-giant stars, their interior, filled with ionized hydrogen and helium, assumes a uniform temperature.
When its interior temperature reaches 100 million degrees Kelvin or more and the density of the core is at least ten kilograms per cubic centimeter, the star begins to produce heavier elements. Two nuclei of helium collide and fuse to produce beryllium-8, releasing energy in the form of gamma rays. Although beryllium-8 has a half life of a billionth of a billionth of a second, some of this element survives to collide with a third helium-4 atom. The resulting nucleus of carbon has six protonsand six neutrons. There may be a further collision between helium and carbon nuclei to produce the nucleus of an element with eight protons and eight neutrons, which is oxygen.
The two new elements join helium in the star’s interior. Oxygen and carbon, being heavier, settle at the core. As heavier elements are formed, the free electrons begin to form atomic bonds. Thermal pressure again balances gravity. The core contracts somewhat as the star continues to fuse carbon from helium nuclei. In a layer surrounding the core, hydrogen atoms fuse into helium. In a layer beyond that, the hydrogen is too cool to support fusion.
The red-giant star thus goes through cycles of contraction and expansion depending upon how much energy is produced internally through fusion relative to the cooling process that takes place on the surface. Meanwhile, energy from the interior passes through the star’s mass and is radiated into space. Each contraction heats up the core and the ionized atoms become more condensed. That, in turn, leads to another expansion followed by a contraction as the surface again cools.
In some cases, however, the expansion occurs with such force that gravity cannot pull the gaseous shell back into place to begin the contracting movement. The star instead ejects its outer layers into space. Up to one-hundred thousandth of a star’s mass can be lost this way each year. Over thousands of years, that would account for a substantial part of its mass.
Stars that have shed their outer layers of gas produce “planetary nebulae”. Ultraviolet radiation from the heated core causes the ejected materials to glow. What remains of a once huge star becomes a small, hot core comprised of helium, carbon, and oxygen atoms. We call those stellar remnants “white dwarfs”. Ninety-eight percent of stars will end that way although the universe as a whole is still in the middle of the stellar process.
WHITE DWARFS AND NEUTRON STARS
White dwarfs are stars of the “main sequence” type in their final phase. Almost all the hydrogen consumed in nuclear fusion has been lost by then. Typically, what remains is an earth-sized core of carbon and oxygen nuclei with perhaps 300,000 times the earth’s mass. Surrounding this is a layer of helium. Another layer of hydrogen is on top.A fog of degenerate electrons that fill the star’s mass exerts pressure to keep gravity from collapsing it further. These floating electrons help the dwarf star maintain a constant density and temperature. Whatever its temperature, the star stays the same size. However, its surface temperature cools since no energy is being produced inside.
Initially, white-dwarf stars are the core of red giants having temperatures of around 150,000 degrees Kelvin. After 30 thousand years, the temperature drops to around 25,000 degrees. Then the cooling process slows as the star becomes less luminous. This phase may last between eight and ten billion years.
Such stars, emitting less radiation, become increasingly hard to detect. They cool even faster if their core consists of oxygen than if it consists of carbon. Knowing this and the current temperature and luminosity, astronomers can determine the star’s age. When a white-dwarf star has exhausted its thermal energy after billions of years, it becomes a cold, inert object called a “black dwarf.”
Occasionally, however, a white dwarf is rejuvenated when it receives material from a neighboring star. The binary star Sirius, brightest in the sky, has a white-dwarf companion. This type of situation could lead to outbursts of novae whereby once dormant stars suddenly produce an explosion of light. In a typical situation, a white dwarf will be a companion star to a red giant. As the latter expands into the dwarf star’s gravitational field, some of its hydrogen mass spills onto that star.
If enough hydrogen accumulates, nuclear explosions could take place hurling large amounts of heated gas into space. The white dwarf then settles down. This process could repeat tens of thousands of years later if the two stars again exchange materials. On the other hand, a nova exploding too energetically could drive the stars apart.
If a star’s exhausted core is between 1.4 and 2 solar masses, it could become a neutron star. Such stars, a million times denser than white dwarfs, are comprised entirely of neutrons, which are particles in the atomic nucleus.
Neutron stars are around 20 kilometers in diameter but have a mass between 1.18 and 1.44 times that of the sun. Their dense interior consists of elemental particles such as kaons, pions, and hyperons. Neutrons in a superfluid state surround this core. The outer layer, comprised of an extremely dense form of iron, is solid although heated to a temperature of 1 million degrees.
Neutron stars have magnetic fields billions of times stronger than the earth’s. This causes the atoms of iron to be arranged in chain-like structures aligned in the direction of the magnetic field.
BINARY STARS, PULSARS, AND BLACK HOLES
Many stars that are close in size to the sun are binary stars. They are a pair of stars bound together by gravity yet maintaining a distance from each other through centrifugal force. The two stars need not be equal in mass. The smaller star is sometimes too faint or too close to the larger one for astronomers to tell them apart. They become aware of it through gravitational influences upon the visible star. One star may also eclipse the other during their regular cycles of pulsation.
Binary stars are often formed in the collapse of larger stars. For instance, if a main-sequence star and neutron star are paired, gaseous materials from the former may be transferred to the neutron star causing the temperature to rise. After flowing to its magnetic pole, the radiation is ejected into space in a stream of X-rays. The Cepheid variables, which are binary stars, go through cycles of varying luminosity. They grow suddenly to a peak of brightness and then gradually fade until the cycle begins again.
Astronomers first became aware of neutron stars through their rotation. A particular type of star called a “pulsar” rotated and emitted pulses of radiation that earthly observers could detect. Neutrons in the star first decayed into protons and electrons which then entered its strong magnetic field. There the particles were accelerated to a speed approaching the speed of light. The rotation acted like a dynamo to produce electromagnetic radiation.
Radio beams were meanwhile released from the pulsar’s magnetic poles. An evenly spaced set of pulses was sent each time the star rotated. The speeds of rotation in pulsars vary from once every 11.8 seconds to 642 times per second. Radio pulsars are gradually slowing down.
Some scientists believe that supernova explosions produce neutron stars. The increasing neutron pressure keeps their core from collapsing. If the mass of the star is greater than three solar masses, however, a neutron star is not produced. Instead, a black hole forms at the collapsed core of a large-sized star that has exhausted its fuel. By the weight of gravity, its mass collapses into a very small space. Inside this, gravity is so strong that nothing can escape. No particles, not even photons of light, can gain the velocity required to escape the gravitational field.That is why black holes are dark. No light is emitted from them. There is a rupturing of space in that place.
The larger the collapsing star, the larger will be the radius of a black hole. The radius will be around 30 kilometers for a star with ten times the mass of the sun. Even though astronomers cannot see what is inside the black hole, they observe what is happening in the surrounding area as nearby objects are affected by its gravitational pull. Matter pouring into a black hole gives off a flood of X-rays. Gases entering this region release more than 100 times as much energy as in nuclear fusion. Then the material simply disappears. Nothing ever returns from this cosmic sinkhole.
Black holes are often found at the center of galaxies. There is one at the center of the Milky Way called “Sagittarius A” whose mass is equivalent to 4.3 million suns.
THE SIZE OF STARS AND ELEMENTAL WEIGHTS
Keep in mind that the universe contains stars at many different stages in their life cycle. Some stars were created not long after the Big Bang. Others such as the sun appeared billions of years later. Because astronomers can see stars in many different phases of their development, they can anticipate the future situation of particular ones. That’s how we add a historical dimension measured in millions and billions of years to information gathered at a particular moment in time.
Another variable in the classification of stars is their size. Size depends on how much cosmic material was picked up by gravity when the star was first created. Stars at one extremity of magnitude produce neutron stars or black holes in the final stage of their lives. Medium-sized stars leave white and black dwarfs. There are also “brown dwarfs” which are too small to support a thermonuclear reaction. Such stars have a mass less than 7.5 percent of the sun’s mass; they are about the size of 75 planets like Jupiter.
Unlike main-sequence stars, brown dwarfs do not convert hydrogen into helium. They produce energy by fusing deuterium for a few million years and then start to contract. The contraction produces temperatures hot enough to fuse hydrogen. Electron degeneracy prevents further contraction as the star stabilizes and fusion stops. A slow cooling process then takes place. The oldest and smallest brown dwarfs have temperatures as low as 500 degrees.There is a limit to the size of stars. Those with a mass of fifty to one hundred times the mass of the sun tend to be unstable. Their gravity creates intense internal pressure which, when it becomes too great, blows the outer layers off into space. A supernova explodes in a spectacular manner. The star is completely destroyed as its materials blast into space.
The larger stars, having more internal pressure, create some of the heavier elements in the periodic table. Their presence on earth indicates that the solar system was formed from the remnant of larger stars that had exploded and sent materials into space.
The first stars formed in the universe were comprised of hydrogen and helium since there was no way to produce heavier elements. Younger stars, by contrast, make use of whatever materials are floating in space, including heavier-element debris left from supernovae explosions. Some of the oldest stars are in groupings of stars called “globular clusters”. Most are over 10 billion years old.
Atoms of lighter elements such as hydrogen, helium, and lithium were created in the aftermath of the big bang. Some helium was also created by nuclear fusion in main-sequence stars. Larger stars fused, first, carbon and oxygen and, then, heavier elements. These elements were not present in the early universe. Heavy elements, even beyond uranium, are still being created in stars. Additionally, more than one hundred different kinds of molecules have been found in outer space.
The material in the universe still consists mostly of hydrogen atoms and molecules. Helium is in second place. An estimate of the most common elements in the universe by mass would be: hydrogen, 71.06%; helium, 23.08%; oxygen, 1.00%; carbon, 0.44%; neon, 0.13%; iron, 0.10%; nitrogen, 0.10%; silicon, 0.06%; magnesium, 0.06%; and sulfur, 0.04%.
This represents 22 pages of English-language text, out of a total of 432 pages for the book.
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