Life Cycle of Stars

A star is a massive body of plasma in outer space that is currently producing or has produced energy through nuclear fusion. Unlike a planet, from which most light is reflected, a star emits light because of its intense heat. Scientifically, stars are defined as self-gravitating spheres of plasma in hydrostatic equilibrium, which generate their own energy through the process of nuclear fusion. Stellar astronomy is the study of stars.

Star formation occurs in molecular clouds, large regions of high density in the interstellar medium (though still less dense than the inside of an earthly vacuum chamber). Star formation begins with gravitational instability inside those clouds, often triggered by shockwaves from supernovae or collision of two galaxies (as in a starburst galaxy). High mass stars powerfully illuminate the clouds from which they formed. One example of such a nebula is the Orion Nebula.

Stars spend about 90% of their lifetime fusing hydrogen to produce helium in high-temperature and high-pressure reactions near the core. Such stars are said to be on the main sequence.

Small stars (called red dwarfs) burn their fuel very slowly and last tens to hundreds of billions of years. At the end of their lives, they simply become dimmer and dimmer, fading into black dwarfs. However, since the lifespan of such stars is greater than the current age of the universe (13.6 billion years), no black dwarfs exist yet.

As most stars exhaust their supply of hydrogen, their outer layers expand and cool to form a red giant. In about 5 billion years, when the Sun is a red giant, it will be so large that it will consume both Mercury and Venus. Eventually the core is compressed enough to start helium fusion, and the star heats up and contracts. Larger stars will also fuse heavier elements, all the way to iron, which is the end point of the process. Since iron nuclei are more tightly bound than any heavier nuclei, they cannot be fused to release energy. Likewise, since they are more tightly bound than all lighter nuclei, energy cannot be released by fission. In old, very massive stars, a large core of inert iron will accumulate in the center of the star.
An average-size star will then shed its outer layers as a planetary nebula. The core that remains will be a tiny ball of degenerate matter not massive enough for further fusion to take place, supported only by degeneracy pressure, called a white dwarf. These too will fade into black dwarfs over very long stretches of time.

In larger stars, fusion continues until an iron core accumulates that is too large to be supported by electron degeneracy pressure. This core will suddenly collapse as its electrons are driven into its protons, forming neutrons and neutrinos in a burst of inverse beta decay. The shockwave formed by this sudden collapse causes the rest of the star to explode in a supernova. Supernovae are so bright that they may briefly outshine the star's entire home galaxy. When they occur within the Milky Way, supernovae have historically been observed by naked-eye observers as "new stars" where none existed before. Eventually, most of the matter in a star is blown away by the explosion (forming nebulae such as the Crab Nebula) and what remains will be a neutron star (sometimes a pulsar or X-ray burster) or, in the case of the largest stars, a black hole.

The blown-off outer layers of dying stars include heavy elements which may be recycled during new star formation. These heavy elements allow the formation of rocky planets. The outflow from supernovae and the stellar wind of large stars play an important part in shaping the interstellar medium.


Supernovae refer to several types of stellar explosions that produce extremely bright objects made of plasma that decline to invisibility over weeks or months. There are two possible routes to this end. A massive star may cease to generate fusion energy from fusing the nuclei of atoms in its core and collapses inward under the force of its own gravity, or a white dwarf star may accumulate material from a companion star until it reaches its Chandrasekhar limit and undergoes a thermonuclear explosion. In either case, the resulting supernova explosion expels much or all of the stellar material with great force.

The explosion drives a blast wave into the surrounding space, forming a supernova remnant. One famous example of this process is the remnant of SN 1604, shown at right.

Supernova explosions are the main source of all the elements heavier than oxygen, and they are the only source of many important elements. In standard cosmology, the Big Bang produced hydrogen, helium, and traces of lithium, while all heavier elements are synthesized in stars and supernovae. For example, all the calcium in our bones and all the iron in our hemoglobin were synthesized in supernova explosions, billions of years ago. Supernovae inject these heavy elements into the interstellar medium, ultimately enriching the molecular clouds that are the sites of star formation. Evidence from daughter products of short-lived radioactive isotopes shows that a nearby supernova helped determine the composition of the Solar System 4.5 billion years ago. Supernova production of heavy elements over cosmic time ultimately made possible the chemistry of life on Earth.

Supernovae generate tremendous temperatures, and under the right conditions, the fusion reactions that take place during the peak moments of a supernova can produce some of the heaviest elements like plutonium and californium.

"Nova" (pl. novae) is Latin for "new", referring to what appears to be a very bright new star shining in the celestial sphere; the prefix "super" distinguishes this from an ordinary nova, which also involves a star increasing in brightness, though to a lesser extent and through a different mechanism. However, it is misleading to consider a supernova as a new star, because it really represents the death of a star (or at least its radical transformation into something else).

Supernovae tend to enrich the surrounding interstellar medium with metals, which for astronomers, include chemical nonmetals after helium. Thus, each stellar generation has a slightly different composition, going from an almost pure mixture of hydrogen and helium to a more metal-rich composition. The different chemical abundances have important influences on the star's life, and may decisively influence the possibility of having planets orbiting it.


A quasar (contraction of QUASi-stellAR radio source) is an astronomical source of electromagnetic energy, including light, that dwarfs the energy output of the brightest stars. A Quasar may readily release energy in levels equal to the output of hundreds of average galaxies combined. In optical telescopes, a quasar looks like a very faint star (i.e. it is a point source), and has a very high redshift. The general consensus is that this high redshift is cosmological, the result of Hubble's law, which implies that quasars must be very distant and hence very luminous.

Some quasars display rapid changes in luminosity, which implies that they are small (an object cannot change faster than the time it takes light to travel from one end to the other; but see J1819+3845 for another explanation). The highest redshift currently known for a quasar is 6.4 [1].
The scientific consensus is that quasars are powered by accretion of material onto supermassive black holes in the nuclei of distant galaxies, making these luminous versions of the general class of objects known as active galaxies. No other mechanism appears able to explain the vast energy output and rapid variability.

Halton Arp

Halton Arp is an American astronomer. He was born born March 21, 1927 in New York city. His bachelor's degree was awarded by Harvard (1949), and his Ph.D. from Caltech (1953). Afterward he became a Fellow of the Carnegie Institution of Washington in 1953, performing research at the Mount Wilson Observatory and Palomar Observatory.

He became a Research Assistant at Indiana University in 1955. In 1957 he became a staff member at Palomar Observatory, where he worked for 29 years. In 1983 he joined the staff of the Max Planck Institute in Germany.
Arp is known for his controversial hypothesis that quasars (QSO's) are local objects ejected from the core of active galactic nuclei (AGN). While very few researchers accept Arp's hypothesis at this time, if Dr. Arp is correct that many QSO's are local, then most of the observed redshift of these QSO's must have a non-cosmological or "intrinsic" origin. This hypothesis is in contrast to the standard view that the observed redshifts of most extragalactic objects is dominated by a cosmological redshift component from expansion of the universe. In his books Dr. Arp has provided his reasons for believing that the Big Bang theory itself is wrong.

The Big Bang is already dead!

"The unheralded "Galileo of the 20th century", Halton Arp, has proven that the universe is not expanding. The Big Bang theory is based on a misinterpretation of redshift. The redshift of a distant galaxy is measured in the light coming from that galaxy. Lines in the spectrum of that galaxy show a shift toward the red compared with the same lines from our Sun. Arp discovered that high and low redshift objects are sometimes connected by a bridge or jet of matter. So redshift cannot be a measure of distance. Most of the redshift is intrinsic to the object. But there is more: Arp found that the intrinsic redshift of a quasar or galaxy took discrete values, which decreased with distance from a central active galaxy. In Arp's new view of the cosmos, active galaxies "give birth" to high redshift quasars and companion galaxies. Redshift becomes a measure of the relative ages of nearby quasars and galaxies, not their distance. As a quasar or galaxy ages, the redshift decreases in discrete steps, or quanta."
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Some ancient Greek philosophers believed in reincarnation; see for example Plato's Phaedo and The Republic. Pythagoras was probably the first Greek philosopher to advance the idea.

We do not know exactly how the doctrine of metempsychosis arose in Greece; most scholars do not believe it was borrowed from Egypt or that it somehow was transmitted from ancient Hindu thinkers of India. It is easiest to assume that earlier ideas which had never been extinguished were utilized for religious and philosophic purposes. The Orphic religion, which held it, first appeared in Thrace upon the semi-barbarous north-eastern frontier. Orpheus, its legendary founder, is said to have taught that soul and body are united by a compact unequally binding on either; the soul is divine, immortal and aspires to freedom, while the body holds it in fetters as a prisoner. Death dissolves this compact, but only to re-imprison the liberated soul after a short time: for the wheel of birth revolves inexorably. Thus the soul continues its journey, alternating between a separate unrestrained existence and fresh reincarnation, round the wide circle of necessity, as the companion of many bodies of men and animals." To these unfortunate prisoners Orpheus proclaims the message of liberation, that they stand in need of the grace of redeeming gods and of Dionysus in particular, and calls them to turn to God by ascetic piety of life and self-purification: the purer their lives the higher will be their next reincarnation, until the soul has completed the spiral ascent of destiny to live for ever as God from whom it comes. Such was the teaching of Orphism which appeared in Greece about the 6th century BC, organized itself into private and public mysteries at Eleusis and elsewhere, and produced a copious literature.

The earliest Greek thinker with whom metempsychosis is connected is Pherecydes; but Pythagoras, who is said to have been his pupil, is its first famous philosophic exponent. Pythagoras probably neither invented the doctrine nor imported it from Egypt, but made his reputation by bringing Orphic doctrine from North-Eastern Hellas to Magna Graecia and by instituting societies for its diffusion.

The real weight and importance of metempsychosis in Western tradition is due to its adoption by Plato. Had he not embodied it in some of his greatest works it would be merely a matter of curious investigation for the Western anthropologist and student of folk-lore. In the eschatological myth which doses the Republic he tells the story how Er, the son of Armenius, miraculously returned to life on the twelfth day after death and recounted the secrets of the other world. After death, he said, he went with others to the place of Judgment and saw the souls returning from heaven and from purgatory, and proceeded with them to a place where they chose new lives, human and animal. He saw the soul of Orpheus changing into a swan, Thamyras becoming a nightingale, musical birds choosing to be men, the soul of Atalanta choosing the honours of an athlete. Men were seen passing into animals and wild and tame animals changing into each other. After their choice the souls drank of Lethe and then shot away like stars to their birth. There are myths and theories to the same effect in other dialogues, the Phaedrus, Meno, Phaedo, Timaeus and Laws. In Plato's view the number of souls was fixed; birth therefore is never the creation of a soul, but only a transmigration from one body to another. Plato's acceptance of the doctrine is characteristic of his sympathy with popular beliefs and desire to incorporate them in a purified form into his system. Aristotle, a far less emotional and sympathetic mind, has a doctrine of immortality totally inconsistent with it.

Belief in reincarnation is an ancient phenomenon; in various guises humans have believed in a future life since the Ancient Egyptians, perhaps earlier, and ancient graves containing both people and possessions may testify to beliefs that a person would have need for their treasured possessions once again despite physical death.
In brief, there are several common concepts of a future life. In each of them either the person, or some essential component that defines that person (variously called the soul or spirit) persists in continuing existence:
People live on this earth, and then live in some kind of afterlife for the rest of eternity - variously called heaven (paradise) or hell, or the Kingdom of the Dead, or some higher plane, or similar. They do not return to earth as such.

People die, but will return to the earth or are revived in some final Judgement, or at some final battle (eg the Norse Ragnarok). They may go to heaven or hell at that time, or live again and repopulate the earth. This is often called an apocalyptic vision of the future.
People die, and are returned to this or another existence continually, their form upon return being of a 'higher' or 'lower' kind depending upon the virtue (moral quality) of their present life. This is often called Transmigration.

People die, go through inner planes and return, re-birth, (usually or often) as new human beings. Strictly, it is this which is known as reincarnation (also called "rebirth"). In many versions, eventually there is the potential to escape the cycle, eg by joining God, enlightenment, some kind of self-realization, a spiritual rebirth, entering a spiritual realm, etc. (There is some confusion, in general society, between reincarnation and transmigration; see below for comparison)

Beliefs in reincarnation or transmigration are widespread amongst religions and beliefs, some seeing it as part of the religion, others seeing in it an answer to many common moral and existential dilemmas, such as "why are we here" and "why do bad things sometimes appear to happen to good people". Reincarnation is therefore a claim that a person has been or will be on this earth again in a different body. It suggests that there is a connection between apparently disparate human lifetimes, and (in most cases) that there may even be covert evidence of continuity between different people's lifetimes, if looked for. Proponents claim this is indeed the case, whilst critics tend to reject the notion due to its metaphysical implications or non-acceptance by science due to other possible explanations of the phenomenon not yet eliminated from consideration.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Reincarnation", Wikipedia article "Halton Arp", Wikipedia article "Supernova" and Wikipedia article "Quasar". The "The Big Bang is Already Dead" excerpt is from