ByWestern Washington Universitylast updated 9/10/2004fromWebsiteIntroductionThe ordinary matter in our universe (known as baryonicmatter) is made up of 94.naturally occurring elements, the familiar beasts of theperiodic table. And it is one of the stunning achievements oftwentieth century science that the question of where these elementscame from has now been answered.The story of the origin of the elements is intimatelyintertwined with the evolution of our universe. It is also a centralpart of the evolution of life on Earth. The elements that make upour bodies reflect the cosmic abundance of the elements, and theirpresents on the Earth is, itself, part of the evolutionary historyof stars.As Neil de Grasse Tyson, anastrophysicist and the director of New York City’s HaydenPlanetarium, has put it:“We are not simply in theuniverse; we are born from it.”(Tyson 1998).Web Reference for Periodic Table.Web Reference for 94 Naturally Occurring ElementsAllan Sandage onStellar Evolution'Historians of science a hundredyears hence will remember twentieth-century astronomy for twomain accomplishments.

• Stellar Origins Human Ways 2011 Pdf

One is the development of a cosmology ofthe early universe, from creation through consequent expansion.The other is the understanding of stellar evolution. Althoughnot as well known among nonscientists as the Big Bang,the notion of the evolution of stars provided the foundationupon which astronomers built the grand synthesis of cosmologicalorigins.The idea that stars change as theyage and that these changes in turn alter their local environmentand the chemical makeup of their parent galaxy—an idea that hasdeveloped only within the past fifty years—stands in the samerelation to astronomy as thedoes tobiology. It is a conceptual breakthrough that makes possible themodern understanding of the origin, evolution, and fate of theuniverse.Because all elements heavier than helium have been nucleo-synthesizedby stars, all the heavier chemical elements that are the rawmaterials of life were one time part of a stellar life cycle.

Weare the product of the stars. This is one of the most profoundinsights to have arisen out of twentieth-century astronomy. Lifeis clearly a property of the evolving universe made possible bystellar evolution.' (Sandage 2000)Web Reference for Allan SandageThe Origin ofthe Light ElementsThe origin of all the naturally occurring elements fall into twophases: Big Bang or Primordial Nucleosynthesis —the origin of the“light” elements; and Stellar Nucleosynthesis— the origin andproduction of the “heavy” elements.When astronomers refer to the “light elements”, they refer mainly tohydrogen and helium and their isotopes, and for very importantreasons. Hydrogen is the simplest possible atom by definition, oneproton and one electron. Anything less and it is no longer an atom;it is a subatomic particle with very different properties from theenergetically stable atom. With this in mind it is easier tounderstand that the most abundant atoms in our universe should bethe ones that formed first from subatomic particles.Big Bang nucleosynthesis refers to the process of element productionduring the early phases of the universe, shortly after the Big Bang.It is thought to be responsible for the formation of hydrogen (H),its isotope deuterium 2H, helium (He) in its varieties 3He and 4He,and the isotope of lithium (Li) 7Li.

Nuclei of hydrogen (protons)are believed to have formed as soon as the temperature had droppedenough to make the existence of free quarks impossible.For a while the number of protons andneutrons was almost the same, until the temperature dropped enoughto make its slight mass difference favor the protons. Isolatedneutrons are not stable, so the ones that survived are the ones thatcould bond with protons to form deuterium, helium, and lithium.Why didn't all the neutrons bond with protons and make all theelements up to iron?While the temperature was dropping, theuniverse was also expanding, and the chances of collision weregetting smaller. Also very important is the fact that there is nostable nucleus with 8 nucleons.

So there was a bottleneck in thenucleosynthesis that stopped the process there. In stars, thisbottleneck is passed by triple collisions of 4He nuclei (thetriple-alpha process), but in the expanding early universe, by thetime there was enough 4He the density of the universe had droppedtoo much to make triple collisions possible.Using the Big Bang model, it is possible to make predictions aboutelemental abundances and to explain some observations which wouldotherwise be difficult to account for. One such observation is theexistence of deuterium.Deuterium is easily destroyed by stars, andthere is no known natural process other than the Big Bang whichwould produce significant amounts of deuterium.Web ReferenceThe observed abundance of baryonic matter in our universe showshydrogen makes up 75% and helium 25% of ordinary matter. Stars that have lost their atmospheres to their companions areidentical to the white dwarves in the center of planetary nebulae.The less massive companion star, assisted by the extra mass it hasgained, eventually becomes a red giant and starts to transfermaterial back onto its white dwarf companion. This can have theeffect of increasing its mass beyond a critical limit of 1.4 timesthe mass of the Sun, known as the Chandrasekhar limit.When this happens the carbon-oxygen corecan suddenly explode, converting half the mass by nuclear fusioninto elements like chromium, manganese, iron, cobalt and nickel.This is called a type Ia supernova.

Because they are very bright andwe think they always explode releasing about the same amount ofenergy, they are used as standard brightness light sources.The recent discovery that the expansionof the universe is accelerating, was made by observing type Iasupernovae in galaxies 5,000 million light years away.Web ReferenceMassive Starsand Type II SupernovaThe most significant locations for the natural alchemy of fusion arestars more massive than our Sun. Although rarer, a heavy starfollows a shorter and more intense path to destruction.To support the weight of the star'smassive outer layers, the temperature and pressure in its core haveto be high.

A star of 20 solar masses is more than 20,000 times asluminous as the sun. Rushing through its hydrogen-fusion phase 1,000times faster, it swells up to become a red giant in just 10 millionyears instead of the Sun's 10 billion.The high central temperature leads as well to a more diverse set ofnuclear reactions. A Sun-like star builds up carbon and oxygen thatstays locked in the cooling ember of a white dwarf. Inside a massivestar, carbon nuclei fuse further to make neon and magnesium. Fusionof oxygen yields silicon as well, along with sulfur.Silicon burnsto make iron. Intermediate stages of fusion and decay make manydifferent elements, all the way up to iron.The iron nucleus occupies a special place in nuclear physics and, byextension, in the composition of the universe.

Stellar Origins Human Ways 2011 Pdf

Iron is the mosttightly bound nucleus. Lighter nuclei, when fusing together, releaseenergy.To make a nucleus heavier than iron, however, requires anexpenditure of energy. This fact, established in terrestriallaboratories, is instrumental in the violent death of stars. Once astar has built an iron core, there is no way it can generate energyby fusion. The star, radiating energy at a prodigious rate, becomeslike a teenager with a credit card.Using resources much faster thancan be replenished, it is perched on the edge of disaster.For massive stars disaster takes the form of asupernova explosion.The core collapses inward in just one second to become a neutronstar or black hole. The material in the core is as dense as thatwithin a nucleus.

The core can be compressed no further. When evenmore material falls into this hard core, it rebounds like a trainhitting a wall.A wave of intense pressure travelingfaster than sound —a sonic boom— thunders across the extent of thestar. When the shock wave reaches the surface, the star suddenlybrightens and explodes. For a few weeks, the surface shines asbrightly as a billion suns while the emitting surface expands atseveral thousand kilometers per second.The abrupt energy release iscomparable to the total energy output of our Sun over its entirelifetime.

Such type II supernova explosions play a special role in thechemical enrichment of the universe.First, unlike stars of low massthat lock up their products in white dwarfs, exploding stars ejecttheir outer layers, which are unburned. They belch out the heliumthat was formed from hydrogen burning and launch the carbon, oxygen,sulfur and silicon that have accumulated from further burning intothe gas in their neighborhood.New elements are also synthesized behind the outgoing shockwave ofthe supernova. The intense heat enables nuclear reactions thatcannot occur in steadily burning stars. Some of the nuclear productsare radioactive, but stable elements heavier than iron can also besynthesized. Neutrons bombard iron nuclei, forging them into gold.Gold is transformed into lead, and lead is bombarded to makeelements all the way up to uranium.

Elements beyond iron in theperiodic table are rare in the cosmos.For every 100 billion hydrogen atoms,there is one uranium atom—each made at special expense in anuncommon setting.Web References-Supernova1987A Seen in InfraredThis theoretical picture of the creation of heavy elements insupernova explosions was thoroughly tested in February 1987. Asupernova, SN 1987A, exploded in the nearby Large Magellanic Cloud.Sanduleak—69° 202, which in 1986 was noted as a star of 20 solarmasses, is no longer there.

Together the star and the supernova givedramatic evidence that at least one massive star ended its life in aviolent way.Neutrinos emitted from the innermost shockwave of the explosion weredetected in Ohio and in Japan, hours before the star began tobrighten. Freshly synthesized elements radiated energy, making thesupernova debris bright enough to see with the naked eye for monthsafter the explosion.

In addition, satellites and balloons detectedthe specific high-energy gamma rays that newborn radioactive nucleiemit.Observations made in 1987 with the International UltravioletExplorer and subsequently with the Hubble Space Telescope supplystrong evidence that Sanduleak—69° 202 was once a red giant starthat shed some of its outer layers. Images taken with the Hubbletelescope revealed astonishing rings around the supernova.The inner ring is material that the star lost when it was a redgiant, excited by the flash of ultraviolet light from the supernova.The outer rings are more mysterious but are presumably related tomass lost from the pre-supernova system. The products of stellarburning are concentrated in a central dot, barely resolved with theHubble telescope, which is expanding outward at 3,000 kilometers persecond.Supernova 1987A has provided dramatic confirmation of elaboratetheoretical models of the origin of elements. Successive cycles ofstar formation and destruction enrich the interstellar medium withheavy elements.Web ReferenceEta CarinaeEta Carinae, thought to be at least 150 solar masses, is asupergiant massive star some 7,500 light years from Earth.

This staris one of the most luminous star systems in our Galaxy, radiatingmillions of times more power than our Sun.Speculation amongastronomers is that Eta Carinae will undergo a supernova explosionsometime in the next thousand years. But because Eta Carinae is overthe 30 solar mass limit of Type II supernovae, it may be destined tobecome a Type Ib/c supernovae associated with ultra luminousgamma-ray bursters.Eta Carinae is also one of the strangest star systems known,brightening and fading greatly since the early 1800s. The HubbleSpace Telescope image above reveals two plumes, made of nitrogen andother elements synthesized in the interior of the star, moving outinto the interstellar void at more than two million miles per hour.Stars destined to become Type IIsupernova, such as Sanduleak—69° 202, may also produce similardischarges.Web ReferenceThe CrabSupernova NebulaWe have come full circle.The universe is the evolutionary story ofgenerations; for every death there is a new beginning. In its deaththroes, supernovae enrich the interstellar medium so that new starsand planets can be born. Every atom of calcium in every bone in ourbodies, every atom of iron in our blood, was shot out of a starbillions of years ago, before the birth of our own Sun.We are literally and actually childrenof the stars.Web References-References.Balick, B., & Frank, A.

(2004).The Extraordinary Deaths of Ordinary Stars. ScientificAmerican, 291(July), 50-59.Gilmore, G. The ShortSpectacular Life of a Superstar. Science, 304(June 25),1915-1916.Sandage, A. Natural History, 2/00, 64-66.Tyson, N. & Goldsmith, D.(2004).

Origins: Fourteen Billion Years of Cosmic Evolution.New York: Norton.Recommended Reading.Silk, Joseph (2001). The BigBang (3rd Edition), New York: W. Freeman.Chown, Marcus (2001). The MagicFurnace: The Search for the Origins of Atoms. New York:Oxford University Press.For more on the origins of the elementson the web go to:.For further information on relatedtopics go to:.