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Thin Disk
The thin disk is a structural component of spiral and S0-type galaxies, composed of stars, gas and dust. It is the main non-centre (e.g. galactic bulge) density, of such matter. That of the Milky Way is thought to have a scale height of around in the vertical axis perpendicular to the disk, and a scale length of around in the horizontal axis, in the direction of the radius. For comparison, the Sun is out from the center. The thin disk contributes about 85% of the stars in the Galactic plane and 95% of the total disk stars. It can be set apart from the thick disk of a galaxy since the latter is composed of older population stars created at an earlier stage of the galaxy formation and thus has fewer heavy elements. Stars in the thin disk, on the other hand, are created as a result of gas accretion at the later stages of a galaxy formation and are on average more metal-rich. The thin disk contains stars with a wide range of ages and may be divided into a series of sub-population ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleocosmochronology
Nucleocosmochronology or nuclear cosmochronology is a technique used to determine timescales for astrophysical objects and events. It compares the observed ratios of abundances of heavy radioactive and stable nuclides to the primordial ratios predicted by nucleosynthesis theory in order to calculate the age of formation of astronomical objects. Nucleocosmochronology has been employed to determine the age of the Sun ( billion years) and of the Galactic thin disk ( billion years), among others. It has also been used to estimate the age of the Milky Way itself, as exemplified by a recent study of Cayrel's Star in the Galactic halo, which due to its low metallicity, is believed to have formed early in the history of the Galaxy. Limiting factors in its precision are the quality of observations of faint stars and the uncertainty of the primordial abundances of r-process elements. See also * Astrochemistry * Geochronology * Gyrochronology Gyrochronology is a method for estimating the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spiral Arm
Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''Alt URL pp. 124–151) and, as such, form part of the . Most spiral galaxies consist of a flat, rotating disk containing s, gas and dust, and a central concentration of stars known as the |
Galactic Spheroid
Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''Alt URL pp. 124–151) and, as such, form part of the . Most spiral galaxies consist of a flat, rotating disk containing s, gas and dust, and a central concentration of stars known as the |
Galactic Halo
A galactic halo is an extended, roughly spherical component of a galaxy which extends beyond the main, visible component. Several distinct components of galaxies comprise the halo: * the stellar halo * the galactic corona (hot gas, i.e. a plasma) * the dark matter halo The distinction between the halo and the main body of the galaxy is clearest in spiral galaxies, where the spherical shape of the halo contrasts with the flat disc. In an elliptical galaxy, there is no sharp transition between the other components of the galaxy and the halo. A halo can be studied by observing its effect on the passage of light from distant bright objects like quasars that are in line of sight beyond the galaxy in question. Components of the galactic halo Stellar halo The stellar halo is a nearly spherical population of field stars and globular clusters. It surrounds most disk galaxies as well as some elliptical galaxies of type cD. A low amount (about one percent) of a galaxy's stellar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Galactic Corona
The terms galactic corona and gaseous corona have been used in the first decade of the 21st century to describe a hot, ionised, gaseous component in the galactic halo of the Milky Way. A similar body of very hot and tenuous gas in the halo of any spiral galaxy may also be described by these terms. Current hypothetical scenario The hypothetical source of the galactic halo of ''coronal gas'' may be the cumulative output of many “galactic fountains” in the galactic disc ejecting hot gas. The hypothesis is that a single supernova and then its supernova remnant both produce hot ionized gas that supplies an individual “galactic fountain”. The expelled material forms a giant bubble of high-pressure, low density, hot gas in the denser, cooler gas and dust of the galactic disc. At least some of those bubbles extend high or low enough, vertically, to pierce through the denser disk, and form “chimneys” which exhaust the hot gas into the halo, analogous to a terrestrial g ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Galaxy Formation And Evolution
The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have generated the variety of structures observed in nearby galaxies. Galaxy formation is hypothesized to occur from structure formation theories, as a result of tiny quantum fluctuations in the aftermath of the Big Bang. The simplest model in general agreement with observed phenomena is the Lambda-CDM model—that is, that clustering and merging allows galaxies to accumulate mass, determining both their shape and structure. Commonly observed properties of galaxies Because of the inability to conduct experiments in outer space, the only way to “test” theories and models of galaxy evolution is to compare them with observations. Explanations for how galaxies formed and evolved must be able to predict the observed properties and types of galaxi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Disc Galaxy
A disc galaxy (or disk galaxy) is a galaxy characterized by a galactic disc, a flattened circular volume of stars. These galaxies may or may not include a central non-disc-like region (a galactic bulge). Disc galaxy types include: * Spiral galaxies: ** Unbarred spiral galaxies: (types S, SA) ** Barred spiral galaxies: (type SB) ** Intermediate spiral galaxies: (type SAB) * Lenticular galaxies: (types E8, S0, SA0, SB0, SAB0) Galaxies that are not disc types include: * Elliptical galaxies: (type dE) * Irregular galaxies: (type dI) See also * thick disk * thin disk The thin disk is a structural component of spiral and S0-type galaxies, composed of stars, gas and dust. It is the main non-centre (e.g. galactic bulge) density, of such matter. That of the Milky Way is thought to have a scale height of around i ... References {{DEFAULTSORT:Disc Galaxy Galaxy morphological types ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Letters
Letter, letters, or literature may refer to: Characters typeface * Letter (alphabet), a character representing one or more of the sounds used in speech; any of the symbols of an alphabet. * Letterform, the graphic form of a letter of the alphabet, either as written or in a particular type font. * Rehearsal letter in an orchestral score Communication * Letter (message), a form of written communication ** Mail * Letters, the collected correspondence of a writer or historically significant person ** Maktubat (other), the Arabic word for collected letters **Pauline epistles, addressed by St. Paul to various communities or congregations, such as "Letters to the Galatians" or "Letters to the Corinthians", and part of the canonical books of the Bible * The letter as a form of second-person literature; see Epistle ** Epistulae (Pliny) ** Epistolary novel, a long-form fiction composed of letters (epistles) * Open letter, a public letter as distinguished from private corresponde ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sofia Feltzing
Johanna Sofia Nikolina Feltzing (born 26 June 1965 in Högsbo, Gothenburg, Sweden) is a Swedish astronomer and Professor of Astronomy at Lund University since 2011. She completed her PhD at Uppsala University in 1996, publishing a dissertation about the chemical evolution of the Milky Way. Feltzing was the first woman to complete a PhD in astronomy at Uppsala, and the tenth in Sweden. She was a postdoctoral researcher at Royal Greenwich Observatory and the Institute of Astronomy, Cambridge at Cambridge University from 1996 to 1998. In 1998 she moved to Lund Observatory. Feltzing's research primarily concerns understanding galaxy formation and evolution by studying the stars and gas of the Milky Way. She has also studied dwarf spheroidal galaxies. and globular star clusters In 2013, Feltzing was awarded the Strömer-Ferrnerska prize of 20,000SEK by the Royal Swedish Academy of Sciences The Royal Swedish Academy of Sciences ( sv, Kungliga Vetenskapsakademien) is one of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spiral Galaxy
Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''Alt URL pp. 124–151) and, as such, form part of the . Most spiral galaxies consist of a flat, rotating disk containing s, gas and dust, and a central concentration of stars known as the |
Thick Disk
The thick disk is one of the structural components of about 2/3 of all disk galaxies, including the Milky Way. It was discovered first in external edge-on galaxies. Soon after, it was proposed as a unique galactic structure in the Milky Way, different from the thin disk and the halo in the 1983 article by Gilmore & Reid. It is supposed to dominate the stellar number density between above the galactic plane and, in the solar neighborhood, is composed almost exclusively of older stars. Its stellar chemistry and stellar kinematics (composition and motion of it stars) are also said to set it apart from the thin disk. Compared to the thin disk, thick disk stars typically have significantly lower levels of metals—that is, the abundance of elements other than hydrogen and helium. The thick disk is a source of early kinematic and chemical evidence for a galaxy's composition and thus is regarded as a very significant component for understanding galaxy formation. With the avail ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
