The globular cluster M80. Messier 80 (also known as M80 or NGC 6093) is a Globular cluster in the Constellation Scorpius. Stars in globular clusters are mainly older metal-poor members of Population II.

In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium. Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study Physical cosmology, as a branch of Astronomy, is the study of the large-scale structure of the Universe and is concerned with fundamental questions about its A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical This terminology should not be confused with the usual meaning of the word 'metal'. Since on the grandest of scales normal (i. In Physics and cosmology, dark matter is hypothetical Matter that does not interact with the electromagnetic force but whose presence can be inferred from e. atomic) matter in the universe is composed overwhelmingly of hydrogen and helium, astronomers label all the heavier elements "metal". The Universe is defined as everything that Physically Exists: the entirety of Space and Time, all forms of Matter, Energy The atomic mass (ma is the Mass of an atom most often expressed in unified atomic mass units The atomic mass may be considered to be the total mass ^[1] Metallic bonds are impossible within stars, and all but the strongest chemical bonds are impossible in all but the coolest layers of "cool" K and M stars, so normal chemistry has little or no relevance in stellar interiors. Although the term metallic bond is often used in contrast to the term Covalent bond it is better to speak of metallic bonding, because this type of bonding is A nebula rich in carbon, nitrogen, oxygen, and neon would be "metal rich" in astrophysical terms even though those elements are nonmetals in conventional chemistry. Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Neon (ˈniːɒn is the Chemical element that has the symbol Ne and Atomic number 10

The metallicity of an astronomical object may provide an indication of its age. When the universe first formed, according to the Big Bang theory, it consisted almost entirely of hydrogen which, through primordial nucleosynthesis, created a sizeable proportion of helium and only trace amounts of lithium and beryllium and no heavier elements. The Big Bang is the cosmological model of the Universe that is best supported by all lines of scientific evidence and Observation. In Physical cosmology, Big Bang nucleosynthesis (or primordial nucleosynthesis) refers to the production of nuclei other than those of H-1 (i Lithium (ˈlɪθiəm is a Chemical element with the symbol Li and Atomic number 3 Beryllium (bəˈrɪliəm is a Chemical element with the symbol Be and Atomic number 4

While older stars do have fewer heavy elements, the fact that all stars observed have some heavier elements poses something of a puzzle, and the current explanation for this involves proposing the existence of Population III stars. Without metals, it is believed that only incredibly massive stars could be formed, and near the end of their lives, created the first 26 elements up to iron in the periodic table via nucleosynthesis. Stellar evolution is the process by which a Star undergoes a sequence of radical changes during its lifetime Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 The periodic table of the chemical elements is a tabular method of displaying the Chemical elements Although precursors to this table exist its invention is Nucleosynthesis is the process of creating new atomic nuclei from preexisting Nucleons (protons and neutrons Because of their high mass, the current model is that they subsequently all died in spectacular supernovae that completely dispersed their material, ejecting those elements throughout the universe, and forming later generations of stars, with heavy elements, that we see today. A supernova (plural supernovae or supernovas) is a stellar Explosion. The high mass of the first stars is used to explain why, as of 2007, no Population III stars have been observed. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Because they were all destroyed in supernovae in the early universe, Population III stars should only be seen in far away galaxies whose light originated much earlier in the history of the universe, and searching for these stars or establishing that they do not exist and hence the model is wrong, is an active area of research in astronomy.

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. This page is about the physical properties of gas as a state of matter 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. A planetary nebula is an Emission nebula consisting of a glowing shell of Gas and plasma formed by certain types of Stars when they die These youngest stars, including the Sun, therefore have the highest metal content, and are known as Population I stars. The Sun (Sol 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 Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply The Galactic Center is the rotational center of the Milky Way Galaxy. 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 forty per cent of the Milky Way, while the Small Magellanic Cloud has a metallicity of about ten per cent of the Milky Way. History The Magellanic Clouds were certainly known since the earliest times by the ancient Middle Eastern peoples An irregular galaxy is a Galaxy that does not fall into any of the regular classes of the Hubble sequence. In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star The Large Magellanic Cloud (LMC is a nearby Satellite galaxy of our own galaxy the Milky Way. The Small Magellanic Cloud (SMC is a Dwarf galaxy. It contains several hundred million stars

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. In Mathematics, the logarithm of a number to a given base is the power or Exponent to which the base must be raised in order to produce (Iron is not the most numerous heavy element, but it is among the easiest to measure with spectral data in the visible spectrum. ) The formula for the logarithm is expressed thus:

where N_Fe and N_H is the number of iron and hydrogen atoms per unit of volume respectively. By this formulation, 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). Powers of Ten is a 1977 short Documentary film written and directed by Ray Eames and her husband Charles Eames. 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.

This same sort of notation is used to express differences in the individual elements from the solar proportion. For example, the notation "[O/Fe]" represents the difference in the logarithm of the star's oxygen abundance compared to that of the Sun and the logarithm of the star's iron abundance compared to the Sun:

The point of this notation is that if a mass of gas is diluted with pure hydrogen, then its [Fe/H] value will decrease (since there are fewer iron atoms per hydrogen atom after the dilution), but for all other elements X, the [X/Fe] ratios will remain unchanged. By contrast, if a mass of gas is polluted with some amount of pure oxygen, then its [Fe/H] will remain unchanged but its [O/Fe] ratio will increase. In general, a given stellar nucleosynthetic process alters the proportions of only a few elements or isotopes, so a star or gas sample with nonzero [X/Fe] values may be showing the signature of particular nuclear processes. Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in Stars to build the nuclei of the heavier elements.

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. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 These are common in the spiral arms of the Milky Way galaxy. A spiral galaxy is a Galaxy belonging to one of the three main classes of galaxy originally described by Edwin Hubble in his 1936 work “The Realm of the The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply

Generally, the youngest stars, the extreme Population I, are found farther in and intermediate Population I stars are farther out, etc. The Sun is considered an intermediate Population I star. Population I stars have regular elliptical orbits of the galactic centre, with a low relative velocity. In Astrodynamics or Celestial mechanics an elliptic orbit is a Kepler orbit with the eccentricity greater than 0 and less than 1 In Kinematics, relative velocity is the vector difference between the velocities of two objects as evaluated in terms of a single Coordinate The high metallicity of Population 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. A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is A terrestrial planet, telluric planet or rocky planet is a Planet that is primarily composed of Silicate rocks Within our In Astrophysics, the term accretion is used for at least two distinct processes ^[4]

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 makeup 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 Population II; and also, in the galactic halo, the halo Population II, which is older and thus more metal-poor. In Astronomy, a bulge is a tightly packed group of Stars The term almost exclusively refers to the central group of stars found in most spiral galaxies. A spiral galaxy is a Galaxy belonging to one of the three main classes of galaxy originally described by Edwin Hubble in his 1936 work “The Realm of the Globular clusters also contain high numbers of Population II stars. A globular cluster is a spherical collection of Stars that orbits a galactic core as a Satellite. ^[5] It is believed that Population II stars created all the other elements in the periodic table, except the more unstable ones. A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. The periodic table of the chemical elements is a tabular method of displaying the Chemical elements Although precursors to this table exist its invention is

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. A quasar (contraction of QUASi-stellAR radio source) is an extremely powerful and distant Active galactic nucleus. 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. |- bgcolor="#FFFAFA"| Distance || 1532952 Yl (47 k pc) BPS CS22892-0052 (Sneden's Star is an old Population II Star \\--> BPS CS31082-0001, named Cayrel's Star, is an old Population II Star located in a distance of 4 kpc in the Galactic |-! style="background-color #FFFFC0" colspan="2" | Astrometry|- style="vertical-align top"| Spectral type | K5+III/dM2 V |- style="vertical-align |-! style="background-color #FFFFC0" colspan="2" | Astrometry|- style="vertical-align top"| Spectral type | K5+III/dM2 V |- style="vertical-align

Population III stars

Probable glow of Population III stars from NASA's Spitzer Space Telescope. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program The Spitzer Space Telescope (formerly the Space Infrared Telescope Facility, SIRTF) is an Infrared Space observatory.
Credit: NASA / JPL-Caltech / A. The California Institute of Technology (commonly referred to as Caltech) is a private, Coeducational research university located in Pasadena Kashlinsky (GSFC)

Population III or metal-free stars (they contained metals at the very end of their lifetimes - we say they're metal-free because the metals exist in the core and are unobservable) are a hypothetical population of extremely massive and hot stars with virtually no metal content, except for a small quantity of metals formed in the Big Bang, such as Lithium-7. The Goddard Space Flight Center ( GSFC) is a major NASA space research laboratory established on May 1, 1959 as NASA's first space flight These stars are believed to have been formed in the early universe. They have not yet been observed directly, but indirect evidence for their existence has been found in a gravitationally lensed galaxy in the very distant universe. A gravitational lens is formed when the light from a very distant bright source (such as a Quasar) is "bent" around a massive object (such as a cluster of ^[6] They are also thought to be components of faint blue galaxies. A faint blue galaxy is a distant irregularly shaped Galaxy in which Star formation occurs at a high rate Their existence is necessary to account for the fact that heavy elements, which could not have been created in the Big Bang, are observed in quasar emission spectra, as well as the existence of faint blue galaxies. An element's 'emission spectrum' is the relative intensity of Electromagnetic radiation of each Frequency it emits when it is Heated (or more generally when ^[7] It is believed that these stars triggered a period of reionization. In Big Bang cosmology, reionization is the process that reionized the matter in the Universe after the " dark ages.

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. Star Formation is the process by which dense parts of Molecular clouds collapse into a ball of plasma to form a Star. Typical masses for Population III stars would be expected to be about several hundred solar masses, which is much larger than the current stars. The solar mass is a standard way to express Mass in Astronomy, used to describe the masses of other Stars and galaxies. Analysis of data on low-metallicity Population II stars, which are thought to contain the metals produced by Population III stars, suggest that these metal-free stars had masses of 10 to 100 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. The James Webb Space Telescope ( JWST) is a planned space Infrared observatory the successor to the aging Hubble Space Telescope. New spectroscopic surveys, such as SEGUE or SDSS-II, may also locate Population III stars. Spectroscopy was originally the study of the interaction between Radiation and Matter as a function of Wavelength (λ The Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic Redshift survey using a dedicated 2 The Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic Redshift survey using a dedicated 2

Simulated image of the first stars, 400 million years after the Big Bang. The Big Bang is the cosmological model of the Universe that is best supported by all lines of scientific evidence and Observation.

The most massive star that can form today is about 110 solar masses with a possible extreme maximum upper limit of 150 solar masses; a more massive protostar would blow itself apart during the initial ignition of nuclear reactions. A protostar is a large object that forms by contraction out of the gas of a Giant molecular cloud in the Interstellar medium. Without enough carbon, oxygen, and nitrogen in the core, however, the CNO cycle could not begin and the star would not destroy itself so readily. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the The core of the Sun is considered to extend from the center to about 0 The CNO cycle (for Carbon - Nitrogen - Oxygen) or sometimes Bethe-Weizsäcker-cycle, is one of two sets of fusion reactions 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. In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus The proton-proton chain reaction is one of several fusion reactions by which Stars convert Hydrogen to Helium, the primary alternative being the The end result would be the star collapsing into a black hole without ever actually shining properly. A black hole is a theoretical region of space in which the Gravitational field is so powerful that nothing not even Electromagnetic radiation (e This is why astronomers consider Population III to be something of a mystery—by all rights they should not exist, yet they are necessary for an explanation of the quasar observations.

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. The James Webb Space Telescope ( JWST) is a planned space Infrared observatory the successor to the aging Hubble Space Telescope.

See also

• Abundance of the chemical elements

Sources

Page 593-In Quest of the Universe Fourth Edition Karl Kuhn Theo Koupelis. See also Abundances of the elements (data page The abundance of a Chemical element measures how relatively common the element is or how much of the element 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.