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Encyclopedia > Metallicity
The globular cluster M80. Stars in globular clusters are mainly older metal-poor members of population II

The metallicity of an astronomical object may provide an indication of its age. When the universe first formed, in accord with the "Big Bang", it consisted almost entirely of hydrogen which, through primordial nucleosynthesis, created a sizeable proportion of helium and only trace amounts of lithium. The first stars, referred to as "Population III", had virtually no metals at all. These stars were incredibly massive and, during their lives, created the elements up to iron in the Periodic Table via nucleosynthesis. They subsequently died in spectacular supernovae which dispersed those elements throughout the universe. As of 2006, no "Pop. III" stars have been found; rather, their existence is inferred in current models of the origin of the universe. The next generation of stars was born out of those materials left by the death of the first. The oldest observed stars, known as "Population II", have very low metallicities;[2] as subsequent generations of stars were born they became more metal-enriched, as the gaseous clouds from which they formed received the metal-rich dust manufactured by previous generations. As those stars died, they returned metal-enriched material to the interstellar medium via planetary nebulae and supernovae, enriching the nebulae out of which the newer stars formed ever further. These youngest stars, including the Sun, therefore have the highest metal content, and are known as "Population I" stars. AGE may refer to: advanced glycation endproduct A.G. Edwards, brokerage firm. ... According to the Big Bang theory, the universe emerged from an extremely dense and hot state (singularity). ... This page is a candidate for speedy deletion. ... General Name, Symbol, Number lithium, Li, 3 Chemical series alkali metals Group, Period, Block 1, 2, s Appearance silvery white/grey Atomic mass 6. ... For alternate meanings see star (disambiguation) Hundreds of stars are visible in this image taken by the Hubble Space Telescope of the Sagittarius Star Cloud in the Milky Way Galaxy. ... In astronomy, stellar evolution is the sequence of radical changes that a star undergoes during its lifetime (the time in which it emits light and heat). ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Atomic mass 55. ... The periodic table of the chemical elements is a tabular method of displaying the chemical elements, first devised in 1869 by the Russian chemist Dmitri Mendeleev. ... Nucleosynthesis is the process of creating new atomic nuclei from preexisting nucleons (protons and neutrons). ... Remnant of Keplers Supernova, SN 1604. ... 2006 is a common year starting on Sunday of the Gregorian calendar. ... There is no universally accepted theory of what the word existence means. ... Scientific modelling is the process of generating abstract or conceptual models. ... The beginning of the universe can refer to either: Big Bang, the scientific theory that describes the origin and evolution of the physical universe. ... Generation (From the Greek Î³Î¹Î³Î½Î¼Î±Î¹), also known as procreation, is the act of producing offspring. ... A gas is one of the four major phases of matter (after solid and liquid, and followed by plasma, that subsequently appear as a solid material is subjected to increasingly higher temperatures. ... After just three years of use, dust has blocked this laptop heat sink, making the computer unusable Dust is a general name for minute solid particles with diameters less than 500 micrometers (otherwise, please see sand or granulates and, more generally, finely divided matter). ... The interstellar medium (or ISM) is the name astronomers give to the tenuous gas and dust that pervade interstellar space. ... NGC 6543, the Cats Eye Nebula A planetary nebula is an astronomical object consisting of a glowing shell of gas and plasma formed by certain types of stars at the end of their lives. ... Multiwavelength X-ray image of the remnant of Keplers Supernova, SN 1604. ... The Sun is the star at the center of the Solar System. ...

Across the Milky Way, metallicity is higher in the galactic centre and decreases as one moves outwards. The gradient in metallicity is attributed to the density of stars in the galactic-centre: there are more stars in the centre of the galaxy and so, over time, more metals have been returned to the interstellar medium and incorporated into new stars. By a similar mechanism, larger galaxies tend to have a higher metallicity than their smaller counterparts. In the case of the Magellanic Clouds, two small irregular galaxies orbiting the Milky Way, the Large Magellanic Cloud has a metallicity of about fourty per cent of the Milky Way, while the Small Magellanic Cloud has a metallicity of about ten per cent of the Milky Way. It has been suggested that Andromeda-Milky Way collision be merged into this article or section. ... The Galactic Center is the rotational center of the Milky Way galaxy. ... In physics, density is defined as mass m per unit volume V. Mathematically, it is expressed as where, in SI units: Ï (rho) is the density of the substance, measured in kgÂ·m-3 m is the mass of the substance, measured in kg V is the volume of the substance... The two Magellanic Clouds are irregular dwarf galaxies that may be orbiting our Milky Way galaxy[1], and thus are members of our Local Group of galaxies. ... NGC1427A, an example of an irregular galaxy. ... In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ... The Large Magellanic Cloud (LMC for short) is a dwarf galaxy that orbits our own galaxy, the Milky Way. ... The percent sign A percentage is a way of expressing numbers as fractions of 100 and is often denoted using the percent sign, %. For example, 45. ... The Small Magellanic Cloud (SMC) is a dwarf galaxy[1] in orbit around the Milky Way Galaxy. ...

## Contents

### Calculation

The metallicity of the Sun is approximately 1.6 percent by mass. For other stars, the metallicity is often expressed as "[Fe/H]", which represents the logarithm of the ratio of a star's iron abundance compared to that of the Sun. The formula for the logarithm is expressed thus: Unsolved problems in physics: What causes anything to have mass? The U.S. National Prototype Kilogram, which currently serves as the primary standard for measuring mass in the U.S. Mass is the property of a physical object that quantifies the amount of matter and energy it is equivalent to. ... Logarithms to various bases: is to base e, is to base 10, and is to base 1. ... A ratio is a dimensionless, or unitless, quantity denoting an amount or magnitude of one quantity relative to another. ... In mathematics and in the sciences, a formula (plural: formulae, formulÃ¦ or formulas) is a concise way of expressing information symbolically (as in a mathematical or chemical formula), or a general relatx E=mcÂ² (see special relativity). ...

$[Fe/H] = log{left(frac{N_{Fe}}{N_H}right)_{star}} - log{left(frac{N_{Fe}}{N_H}right)_{sun}}$

Here NFe and NH is the number of iron and hydrogen atoms per unit of volume respectively. By this formulation therefore, stars with a higher metallicity than the Sun have a positive logarithmic value, while those with a lower metallicity than the Sun have a negative value. The logarithm is based on powers of ten; stars with a value of +1 have ten times the metallicity of the Sun (101), while those with +2 have a hundred (10²) and those with +3 have a thousand (10³). Conversely, those with a value of -1 have one tenth (10 -1), while those with -2 have a hundredth (10-2) and so on.[3] Young "Population I" stars have significantly higher iron-to-hydrogen ratios than older "Population II" stars. Primordial "Population III" stars are estimated to have a metallicity of less than −6.0, that is, less than a millionth of the abundance of iron which is found in the Sun. Properties For alternative meanings see atom (disambiguation). ... The volume of a solid object is the three-dimensional concept of how much space it occupies, often quantified numerically. ... In common usage positive is sometimes used in affirmation, as a synonym for yes or to express certainty. Look up Positive on Wiktionary, the free dictionary In mathematics, a number is called positive if it is bigger than zero. ... Negative has meaning in several contexts: Look up negative in Wiktionary, the free dictionary. ... Powers of Ten is a 1977 short documentary film which depicts the relative scale of the Universe in factors of ten (see also logarithmic scale and order of magnitude). ...

### "Population I" stars

Populations "I" and "II"

"Population I" or "metal-rich" stars are those young stars whose metallicity is highest. The Earth's Sun is an example of a "metal-rich" star. These are common in the spiral arms of the Milky Way galaxy. Image File history File links Starpop. ... Image File history File links Starpop. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... A spiral galaxy presents a face-on view of its spiral arms. ... It has been suggested that Andromeda-Milky Way collision be merged into this article or section. ...

Generally, the youngest stars, the extreme "Pop. I", are found further in and intermediate "Pop. I" stars are further out, etc. The Sun is considered an intermediate "Pop. I" star. "Pop. I" stars have regular elliptical orbits of the galactic centre, with a low relative velocity. The high metallicity of "Pop. I" stars makes them more likely to possess planetary systems than the other two populations, since planets, particularly terrestrial planets, are formed by the accretion of metals.[4] In astrodynamics or celestial mechanics a elliptic orbit is an orbit with the eccentricity greater than 0 and less than 1. ... Relative velocity is a measurement of velocity between two objects moving in different frames of reference. ... An artists concept of a protoplanetary disc. ... A planet (from the Greek &#960;&#955;&#945;&#957;&#942;&#964;&#951;&#962;, planetes or wanderers) is a body of considerable mass that orbits a star and that produces very little or no energy through nuclear fusion. ... The inner planets, their sizes to scale. ... See also: Accretion (finance) Accretion is increase in size by gradual addition of smaller parts. ...

Between the intermediate populations "I" and "II" comes the intermediary "disc population".

### Population II stars

"Population II" or "metal-poor" stars are those with relatively little metal. The idea of a "relatively" small amount must be kept in perspective as even "metal-rich" astronomical objects contain low quantities of any element other than hydrogen or helium; metals constitute only a tiny percentage of the overall chemical make up of the universe, even 13.7 billion years after the "Big Bang". However, "metal-poor" objects are even more primitive. These objects formed during an earlier time of the universe. They are common in the bulge near to the centre of the galaxy, the intermediate "Pop. II" and also, in the galactic halo, the halo "Pop. II", which is older and thus more "metal-poor". Globular clusters also contain high numbers of "Pop. II" stars.[5] It is believed "Pop. II" stars created all the other elements in the Periodic Table, excepting the more "unstable" ones.
Scientists have targeted these oldest stars in several different surveys, including the HK objective-prism survey of Timothy C. Beers et al. and the Hamburg-ESO survey of Norbert Christlieb et al., originally started for faint quasars. Thus far, they have uncovered and studied in detail about ten very "metal-poor" stars (as CS22892-052, CS31082-001, BD +17° 3248) and two of the oldest stars known to date: HE0107-5240 and HE1327- 2326. Look up time in Wiktionary, the free dictionary. ... In astronomy, a bulge is a huge, tightly packed group of stars. ... Spiral galaxies have a typical structure related to their history. ... A globular cluster is a spherical bundle of stars (star cluster) that orbits a galaxy as a satellite. ... See: Prism (geometry) Prism (optics) Prism (band) PRISM is an abbreviation for Probabilistic Symbolic Model Checker PRISM was an aborted RISC processor effort at DEC, see DEC PRISM This is a disambiguation page &#8212; a navigational aid which lists other pages that might otherwise share the same title. ... Hamburg from above Hamburgs motto: May the posterity endeavour with dignity to conserve the freedom, which the forefathers acquired. ... The European Southern Observatory (ESO) is an international astronomical organisation, composed and supported by ten countries from the European Union plus Switzerland. ... This view, taken with infrared light, is a false-color image of a quasar-starburst tandem with the most luminous starburst ever seen in such a combination. ... BPS CS22892-0052 (Snedens Star) is an old Population II star located in a distance of 4. ... BPS CS31082-0001 (Cayrels Star) is an old star located in a distance of 4 kpc in the Galactic Halo. ... BD +17Â° 3248 (Karl-Ludwig Kratzs Star ) is an old Population II star located in a distance of 272 pc in the Galactic Halo. ... HE0107-5240 is a newly discovered giant star roughly 36,000 light years away from Earth. ... HE1327-2326, discovered in 2005, is the star with the lowest known iron abundance to date. ...

### "Population III" stars

Probable glow of "Population III" Stars from NASA's Spitzer telescope.
Credit: NASA / JPL-CALTECH / A. KASHLINSKY (GSFC)

Current theory is divided on whether the first stars were very massive or not. One theory, which seems to be borne out by computer models of star formation, is that with no "heavy" elements from the "Big Bang", it was easy to form stars with much more total mass than the ones visible today. Typical masses for "Population III" stars would be expected to be about several hundred solar masses, which is much larger than the current stars. Analysis of data on low-metallicity "Pop. II" stars, which are thought to contain the metals produced by "Pop. III" stars, suggest that these "metal-free" stars had masses of ten to one-hundred solar-masses instead. This also explains why there have been no low-mass stars with zero metallicity observed. Confirmation of these theories awaits the launch of NASA's James Webb Space Telescope. New spectroscopic surveys, such as SEGUE or SDSS-II, may also locate "Population III" stars. The word theory has a number of distinct meanings in different fields of knowledge, depending on their methodologies and the context of discussion. ... A BlueGene supercomputer cabinet. ... Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... Look up Analysis in Wiktionary, the free dictionary An analysis is a critical evaluation, usually made by breaking a subject (either material or intellectual) down into its constituent parts, then describing the parts and their relationship to the whole. ... In general, data consist of propositions that reflect reality. ... Look up zero in Wiktionary, the free dictionary. ... Uses of the word launch: A launch can be a type of boat: see launch (boat). ... The James Webb Space Telescope (JWST) is a planned space infrared observatory, intended to be a significant improvement on the aging Hubble Space Telescope. ... Spectroscopy is the study of spectra, ie. ... There are several uses of the word survey. ...

Simulated image of the first stars, 400 Ma after "Big Bang". Acknowledgement: NASA/WMAP Science Team.

The highest-mass star which may form today is about one-hundred and ten solar-masses. Any attempt to form a star greater than this results in the protostar blowing itself apart during the initial ignition of nuclear reactions. Without enough carbon, oxygen and nitrogen in the core, however, the CNO cycle could not begin and the star would not go nuclear with such enthusiasm. Direct fusion through the proton-proton chain does not proceed quickly enough to produce the copious amounts of energy such a star would need to support its immense bulk. The end result would be the star collapsing into a black hole without ever actually shining properly. This is why astronomers consider "Pop. III" to be something of a mystery--by all rights they should not exist, yet they are necessary for an explaination of the quasar observations. Image File history File links NASA-WMAP-first-stars. ... Image File history File links NASA-WMAP-first-stars. ... A Protostar is an object that forms by contraction out of the gas of a giant molecular cloud in the interstellar medium. ... Ignition occurs when the heat produced by a reaction becomes sufficient to sustain the reaction, whether it be a fire, an explosion, or nuclear fusion. ... The word nuclear means of or belonging to the nucleus of something. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ... The structure of the Sun The core of the Sun is considered to extend from the center to about 0. ... This article does not cite its references or sources. ... Look up fusion in Wiktionary, the free dictionary. ... The proton-proton chain reaction is one of two fusion reactions by which stars convert hydrogen to helium, the other being the CNO cycle. ... A black hole is an object with a gravitational field so powerful that even electromagnetic radiation (such as light) cannot escape its pull. ... Luminosity has different meanings in several different fields of science. ... Look up mystery in Wiktionary, the free dictionary. ...

If these stars were able to form properly, their lifespan would be extremely short, certainly less than one million years. As they can no longer form today, viewing one would require us to look to the very edges of the observable universe, since the time it takes light to reach Earth from great distances is extremely great, it is possible to see "back in time" by looking farther away. Seeing to this distance while still being able to resolve a star could prove difficult, even for the James Webb Space Telescope. Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength[1]. The elementary particle that defines light is the photon. ...

Suspected "Pop. II" stars include:

• HE1327-2326
• HE0107-5240

HE1327-2326, discovered in 2005, is the star with the lowest known iron abundance to date. ... HE0107-5240 is a newly discovered giant star roughly 36,000 light years away from Earth. ...

The abundance of a chemical element measures how common the element is, or how much of the element there is. ...

## Sources

Page 593-In Quest of the Universe Fourth Edition Karl Kuhn Theo Koupelis. Jones and Bartlett Publishers Canada. 2004. ISBN 0-7637-0810-0

Volker Bromm, Richard B. Larson (2004), THE FIRST STARS, Annual Reviews of Astronomy and Astrophysics, vol. 42, pp. 79–118.

1. ^ John C. Martin. What we learn from a star's metal content. New Analysis RR Lyrae Kinematics in the Solar Neighborhood. Retrieved on September 7, 2005.
2. ^ Lauren J. Bryant. What Makes Stars Tick. Indiana University Research & Creative Activity. Retrieved on September 7, 2005.
3. ^ John C. Martin: What we learn from a star's metal content.
4. ^ Charles H. Lineweaver (2000). An Estimate of the Age Distribution of Terrestrial Planets in the Universe: Quantifying Metallicity as a Selection Effect. University of New South Wales. Retrieved on 2006-07-23.
5. ^ T. S. van Albada, Norman Baker (1973). "On the Two Oosterhoff Groups of Globular Clusters". Astrophysical Journal 185: 477–498.
6. ^ R. A. E. Fosbury et al. (2003). "Massive Star Formation in a Gravitationally Lensed H II Galaxy at z = 3.357". Astrophysical Journal 596 (1): 797-809.
7. ^ A. Heger, S. E. Woosley (2002). "The Nucleosynthetic Signature of Population III". Astrophysical Journal 567 (1): 532-543.

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