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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-populations ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleocosmochronology
Nucleocosmochronology, or nuclear cosmochronology, is a technique used to determine timescales for astrophysics, astrophysical objects and events based on observed ratios of radioactive heavy elements and their decay products. It is similar in many respects to radiometric dating, in which trace radioactive impurity, impurities were selectively incorporated into materials when they were formed. To calculate the age of formation of astronomical objects, the observed ratios of Abundance of the chemical elements, abundances of heavy radionuclide, radioactive and stable nuclides are compared to the primordial ratios predicted by Nucleosynthesis, nucleosynthesis theory. Both radioactive elements and their decay products matter, and some important elements include the long-lived radioactive nuclei Th-232, Uranium-235, U-235, and Uranium-238, U-238, all formed by the r-process. The process has been compared to radiocarbon dating. The age of the objects are determined by placing constraint ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spiral Arm
Spiral arms are a defining feature of spiral galaxies. They manifest as spiral-shaped regions of enhanced brightness within the galactic disc. Typically, spiral galaxies exhibit two or more spiral arms. The collective configuration of these arms is referred to as the spiral pattern or spiral structure of the galaxy. The appearance of spiral sleeves is quite diverse. Grand design spiral galaxy, Grand design spiral galaxies exhibit a symmetrical and distinct pattern, comprising two spiral arms that extend throughout the galaxy. In contrast, the spiral structure of flocculent galaxies comprises numerous small fragments of arms that are not connected to each other. The appearance of spiral arms varies across the electromagnetic spectrum. In addition to increased brightness, spiral arms are characterised by an increased concentration of interstellar medium, interstellar gas and dust, bright stars and star clusters, active starburst region, starburst, a bluer colour, and an enhanced mag ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Galactic Spheroid
Galactic is an American funk band from New Orleans, Louisiana. Origins and background Formed in 1994 as an octet (under the name Galactic Prophylactic) and including singer Chris Lane and guitarist Rob Gowen, the group was soon pared down to a sextet of: guitarist Jeff Raines, bassist Robert Mercurio, drummer Stanton Moore, Hammond organist Rich Vogel, Theryl DeClouet on vocals, and later adding saxophonist Ben Ellman. The group was started when Raines and Mercurio, childhood friends from affluent Chevy Chase, Maryland, moved to New Orleans together to attend college at Tulane and Loyola University New Orleans, Loyola Universities, became enamored of the local funk scene, populated by such legendary acts as The Meters and Dirty Dozen Brass Band and inspired by local legends such as Professor Longhair. There they teamed with noted New Orleans drummer Stanton Moore, saxophonist/harmonica (now producer) Ben Ellman, Rich Vogel, and Theryl de Clouet. In 2004, the band parted ways wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 a galaxy comprise its 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 ge ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Galaxy Formation And Evolution
In cosmology, 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, clustering and merging allows galaxies to accumulate mass, determining both their shape and structure. Hydrodynamics simulation, which simulates both baryons and dark matter, is widely used to study galaxy formation and evolution. 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 th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Disc Galaxy
A disc galaxy (or disk galaxy) is a galaxy characterized by a galactic disc. This is a flattened circular volume of stars that are mainly orbiting the galactic core in the same plane. These galaxies may or may not include a central non-disc-like region (a galactic bulge). They will typically have an orbiting mass of gas and dust in the same plane as the stars. Interacting galaxy, Interactions with other nearby galaxies can perturb and stretch the galactic disk. Disc galaxy types include: * Spiral galaxy, Spiral galaxies: ** Unbarred spiral galaxy, Unbarred spiral galaxies: (types S, SA) ** Barred spiral galaxy, Barred spiral galaxies: (type SB) ** Intermediate spiral galaxy, Intermediate spiral galaxies: (type SAB) * Lenticular galaxy, Lenticular galaxies: (types E8, S0, SA0, SB0, SAB0) Galaxies that are not disc types include: * Elliptical galaxy, Elliptical galaxies: (type dE) * Irregular galaxy, Irregular galaxies: (type dI) See also * thick disk * thin disk References [...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 or none in the case of a silent letter; 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 **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 ** Maktubat (other), the Arabic word for collected letters * 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 d ... [...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. Feltzing was the first woman to complete a PhD in astronomy at Uppsala, and the tenth in Sweden. Biography Feltzing completed her PhD at Uppsala University in 1996, publishing a dissertation about the chemical evolution of the Milky Way. 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 () is one of the Swedish Royal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spiral Galaxy
Spiral galaxies form a galaxy morphological classification, 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 Hubble sequence. Most spiral galaxies consist of a flat, rotating Disc (galaxy), disk containing stars, Interstellar medium, gas and dust, and a central concentration of stars known as the Bulge (astronomy), bulge. These are often surrounded by a much fainter Galactic halo, halo of stars, many of which reside in globular clusters. Spiral galaxies are named by their spiral structures that extend from the center into the galactic disc. The spiral arms are sites of ongoing star formation and are brighter than the surrounding disc because of the young, hot OB stars that inhabit them. Roughly two-thirds of all spirals are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 distinct 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. For the Milky Way, the thick disk has a scale height of around in the axis perpendicular to the disk, which is 3-4 times larger than the thin disk, and a scale length of around in the horizontal axis, in the direction of the radius. 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 A metal () is a material t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
