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Wednesday, 24 June 2015

First Star Formation in the galaxy III generation star formation



We generally think of stars in populations. PopulationIII stars were so long the hypothetical first stars in cosmos. These stars are extremely metal poor but massive stars composed of geasses. By metals I amtalking about elements heavier than hydrogen (and helium depending on which
definition you read and is what I consider to be a non-metal too). All elements heavier than hydrogen are a by-product or ash from fusion within the cores of stars. Population II stars group however
have also very little metals, and stars in globular clusters are made up of a good percentage of such population II stars. Population II stars are till date considered to have created all other elements found in the periodic table beyond hydrogen and helium. Prior to 1978 or 1979 these were the stars
thought to be the oldest stars and still are the oldest observed stars in the observable cosmos. Population I stars are considered very metal rich young stars and they include our own Sun
and are common in the arms of our galaxy the Milky Way. Many astronomers have for long theorized existence of first generation of such stars — known as Population III stars as stated by me — that were in fact born out of the primordial materials from the Big Bang event. All the heavier chemical elements — such as oxygen, nitrogen, Lithium ,carbon and iron, which are essential to create life — were then frozen in the bellies of stars. This means that the first stars must had formed out of the only elements to exist prior to stars called Protostars: hydrogen, helium and trace amounts of lithium. These Population III stars would have been enormous — several hundred or even a thousand times more massive than our Sun is — blazing hot, and transient — exploding as supernovae after only about two million years. But until now the search for physical proof of theirexistence had been inconclusive. A team in 2015 led by David Sobral, from theInstitute of Astrophysics and Space Sciences, the Faculty of Sciences of theUniversity of Lisbon in Portugal, and Leiden Observatory in the Netherlands, has now used ESO’s Very Large Telescope (VLT) to peer back into the ancient
Universe, to a period known as re-ionisation, approximately 800 million years after the Big Bang. Instead of conducting a narrow and deep study of a small area of the sky, they broadened their scope to produce the widest survey of very distant galaxies ever attempted. According to conventional cosmological theory, all space, time, andenergy began with the Big Bang, now estimated to have occurred around 13.8billion years ago . In a new twist to standard theoretical models, however, many astrophysicists now believe that the universe may have suddenly inflated (
inflation theory of Alan Guth) from a tiny point after this incredible explosion to create dark energy (74 percent) and dark matter (22 percent), as well as a small amount (04 percent) of ordinary matter we see in universe inthe form of electrons and quarks or nutrinos in a superhot plasma (more on the
proportion of matter in the "Cinderella Universe" model from SDSS). Within the first second after the Big Bang, the quark gluon plasma may have cooled enough forquarks to combine and formed protons (the most common atomic nuclei of hydrogen) and neutrons. After about three minutes, a small portion of the neutrons avoided decay by bonding with protons (to produce deuterons, the
atomic nuclei of the deuterium form of hydrogen) which underwent rapid reactions to form helium and a trace of lithium. For a few hundred thousand years afterwards, however, the universe still remained extremely hot at around a billion degrees and so ordinary matter remained then ionized, as a plasma of positively charged ions and unbound, negatively charged electrons. Three to four hundred thousand years have then passed before continuing cosmological expansion and cooling enabled atomic nuclei to hold onto electrons and create neutral hydrogen and helium gas (alongwith a trace of lithium at around a redshift of z ~ 1,000). Measurements of themodern universe suggest that, by mass, about three-fourths of the ordinarymatter formed from the Big Bang became hydrogen while virtually all of the rest became helium; by number, around nine-tenths of all atoms may still be
hydrogen, while roughly nine percent has become helium. After this initial cooling, the early universe became extremely dark. Although cosmic microwave background radiation from around 380,000 years after the Big Bang suggest that the early universe was remarkably smooth, very small-scale density fluctuations (possibly related to small variations in early cosmological inflation predicted
by quantum mechanics) may have led to uneven concentrations in the primordial distribution of matter in the universe, of which around nine-tenths may be comprised of dark matter(CDM). While
particles of ordinary matter readily interact with one another and, if electrically charged, with electromagnetic radiation, dark matter is comprised of particles that do not react with such radiation, although dark matter interacts gravitationally just like ordinary matter. In theory, gravitational attraction should have caused these dark matter density variations to condense into a network of filaments and sheets over time. Unlike ordinary matter, however, the dark matter hypothesized by theorists either cannot or mostly did not collapse into dense objects like stars, brown dwarfs,
and stellar remnants (white dwarfs, neutron stars, and black holes) Although dark matter is thought to be relatively segregated from ordinary baryonic matter in outer galactic halos and intergalactic space today, the two may have been mixed initially. As the dark matter condensed into a denser filamentary network, ordinary matter made of hydrogen and helium gas also was gravitationally attracted by these relative concentrations of dark matter, creating Lyman-alpha "forest" clouds of gas. At the nodes of the dark matter filaments, these gas clouds collapsed under gravitation towards of the cores of denser clumps of 100,000 to one million Solar-masses that may have measured around 30 to 100 light-years across and still consisted mostly of dark matter. As the gas clouds contracted, compression would have heated the gas to temperatures above 1,000° Kelvin (727° C or 1,340° F). Some hydrogen atoms would have paired up within the dense, hot gas to create molecular hydrogen, which would then help to cool the densest parts of the gas cloud by emitting infrared radiation after collision with atomic hydrogen. Eventually, the temperature in the densest regions of such clouds would drop to around 200 to 300° Kelvin (-73 to 27° C or -100 to 80° F), reducing the gas pressure and allowing the cloud to continue contracting into gravitationally bound clumps The
results of various simulations by several teams of astronomers suggest that these nearly "metal-free" clumps were able to resist fragmentation into smaller clumps. Hence, the first stars (often they are called Population III stars) may havebeen very massive, hot, and bright, with 100 to 1,000 Solar-masses (more discussion on Jeans mass and metal-free stars . At least one simulation suggests
that only one massive star may haveformed for each proto-galactic clump because of resistance to renewedfragmentation of the star-forming cloud and intense radiation once the star isformed. Various computer simulations suggest that the first stars could haveappeared between 100 and 250 million years after the Big Bang, when the universe had expanded to at least 1/30 of its present size. In 2003, astronomers announced that analyses of NASA's recent WMAP satellite images of the
cosmic microwave background indicate that this primordial light was ionized by the first generation of stars, which may have come and gone within only 400 million years after the Big Bang , but further analysis of data led astronomers to conclude by March 2006 that ionization may not have occurred as much as 400 million years after the Big Bang latest WMAP results). When this first generation of massive stars lighted up, the so-called "Cosmic Dark Age" ended. And first light(Photon) of universe came out . Even then, these stars were surrounded by a "fog" of light-absorbing neutral hydrogen . The first stars, however, began emitting intense ultraviolet radiation -- perhaps as much as a million times that of Sol -- that "re-ionized" neutral hydrogen atoms by energizing electrons away from
their proton nuclei (Larson and Bromm, Scientific American, December 2001, in pdf). Gradually,
the first stars created ever-wider bubbles of clearer space. Since these stars were short lived, it probably took another generation of stars and a few hundred million years for that hydrogen fog to dissipate, as strong absorption of ultraviolet light from quasars dating to 860 to 900 million or so years after the Big Bang suggest that the last patches of neutral hydrogen were being
ionized at that time. OnJuly 31, 2008, a team of astronomers (led by Naoki Yoshida) announcedthat new simulation results which indicate that the first stars formed within 300 million years after the Big Bang. First, "seed" proto-stars formed from the collapsing core of gas clouds that go through a stage as a flattened disc, with two trailing spiral arms of gas. Despite having only only 0.1 Solar-mass, the proto-stars quickly "bulked up" on surrounding gases into behemoths of at least 100 Solar-masses within 10,000 years. After a million years as a very bright star, some of these massive stars may have become supernovae -- depending on their mass On December 3, 2007, a team of theoretical physicists (including Katherine Freese, Douglas Spolyar, and Paolo Gondolo) released the results of a paper which suggests that the first proto-stars could have been powered by the annihilation of opposite forms of dark matter (Weakly Interacting Massive Particles or WIMPs, such as neutralinos). In theory, each dark matter particle should have its own anti-particle. When such particle pairs meet, they would annihilate each other, whereby one-third of the resulting energy is produced as neutrinos which escape, one-third becomes gamma-ray photons, and the last third becomes electrons and positrons.
A team led by David Sobral, from the Institute of Astrophysics and Space Sciences, the Faculty of Sciences of the University of Lisbon in Portugal, and Leiden Observatory in the Netherlands, has now used ESO's Very Large Telescope to peer back into the ancient Universe, to a period known as reionisation, approximately 800 million years after the Big Bang. Instead of conducting a narrow and deep study of a small area of the sky, they broadened their scope to produce the widest survey of very distant galaxies ever attemptedTheir expansive study was made using the VLT with help from the W. M. Keck Observatory and the Subaru Telescope as well as the NASA/ESA Hubble Space Telescope. The team discovered -- and confirmed -- a number of surprisingly bright very young galaxies. One of these, labelled CR, was an exceptionally rare object, by far the brightest galaxy ever observed at this stage in the Universe [4]. With the discovery of CR7 and other bright galaxies, the study was already a success, but further inspection provided additional exciting news.[1]
CR7's nickname is an abbreviation of COSMOS Red shift 7, a measure of its place in terms of cosmic time. The higher the red shift, the more distant the galaxy and the further back in the history of the Universe it is seen. A1689-zD1 , one of the oldest galaxies ever observed, for example, has a redshift of 7.5.

 References

 1] ESO. "Best observational evidence of first generation stars in the universe: VLT discovers CR7, the brightest distant galaxy, and signs of Population III stars."  Science Daily, 17 June 2015. www.sciencedaily.com/releases/2015/06/150617092409.htm.

2] Comment of Professor Pranab kumar Bhattacharya on article  Astronomers spot first-generation stars, made from big bang at Science of AAAS.org By   17 June 2015 6:00 am
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