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Protostar
A protostar is a very young star that is still gathering mass from its parent molecular cloud. It is the earliest phase in the process of stellar evolution. For a low-mass star (i.e. that of the Sun or lower), it lasts about 500,000 years. The phase begins when a molecular cloud fragment first collapses under the force of Self-gravitation, self-gravity and an opaque, pressure-supported core forms inside the collapsing fragment. It ends when the infalling gas is depleted, leaving a pre-main-sequence star, which contracts to later become a main-sequence star at the onset of hydrogen Nuclear fusion, fusion producing helium. History The modern picture of protostars, summarized above, was first suggested by Chushiro Hayashi in 1966. In the first models, the size of protostars was greatly overestimated. Subsequent numerical calculations clarified the issue, and showed that protostars are only modestly larger than main-sequence stars of the same mass. This basic theoretical result has b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
HOPS 383
HOPS 383 is a Class 0 protostar. It is the first Class 0 protostar discovered to have had an outburst, and as of 2020, the youngest protostar known to have had an outburst. The outburst, discovered by the Herschel Orion Protostar Survey (HOPS) team, was first reported in February 2015 in ''The Astrophysical Journal, The Astrophysical Journal Letters''. Observations Outburst HOPS 383 had an outburst between 2004 and 2006 (a "dramatic mid-infrared brightening"); the increase in Magnitude (astronomy), magnitude was detectable at the 24 μm (35 times increase) and 4.5 μm, and was also detectable at the Submillimetre astronomy, submillimetre. After 6 years, observations showed no signs of fading. X-Ray The Chandra X-ray Observatory, Chandra X-Ray Observatory detected an X-ray flare from HOPS 383 in December 2017. This was the first detection of X-rays from a Class 0 protostar that will evolve into a sun-like star. The flare lasted 3 hours and 20 minutes. It significantly ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stellar Evolution
Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is considerably longer than the current age of the universe. The table shows the lifetimes of stars as a function of their masses. All stars are formed from Gravitational collapse, collapsing clouds of gas and dust, often called nebulae or molecular clouds. Over the course of millions of years, these protostars settle down into a state of equilibrium, becoming what is known as a main sequence star. Nuclear fusion powers a star for most of its existence. Initially the energy is generated by the fusion of hydrogen atoms at the stellar core, core of the main-sequence star. Later, as the preponderance of atoms at the core becomes helium, stars like the Sun begin to fuse hydrogen along a spherical shell surrounding the core. This process causes the st ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
V1647 Orionis
V1647 Orionis ( V1647 Ori) is a young stellar object visible in the constellation Orion, located about 1470 light-years from the Solar System. It is situated in the reflection nebula M78 and is associated with McNeil's Nebula. The object is known to have experienced intense eruptive phenomena on several occasions (the last of which occurred in 2008), the characteristics of which have led to the object being considered a middle ground between two classes of pre-main-sequence star, FU Orionis (FUor) and EX Lupi (EXor). Characteristics Studies have revealed that V1647 Orionis is a young stellar object, presumably a pre-main sequence star; the age of the object, based on evolutionary models and data obtained, is between 100,000 and half a million years. Like all forming stars, V1647 Orionis has a disk of gas and silicate dust in its orbit, which mediates the accretion of the star, surrounded by a gas envelope that replenishes the disk with material. The accretion pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pre-main-sequence Star
A pre-main-sequence star (also known as a PMS star and PMS object) is a star in the stage when it has not yet reached the main sequence. Earlier in its life, the object is a protostar that grows by acquiring mass from its surrounding envelope of interstellar dust and gas. After the protostar blows away this envelope, it is optically visible, and appears on the stellar birthline in the Hertzsprung-Russell diagram. At this point, the star has acquired nearly all of its mass but has not yet started hydrogen burning (i.e. nuclear fusion of hydrogen). The star continues to contract, its internal temperature rising until it begins hydrogen burning on the zero age main sequence. This period of contraction is the pre-main sequence stage. An observed PMS object can either be a T Tauri star, if it has fewer than 2 solar masses (), or else a Herbig Ae/Be star, if it has 2 to 8 . Yet more massive stars have no pre-main-sequence stage because they contract too quickly as protostars. By t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
HH 46/47
HH 46/47 is a complex of Herbig–Haro objects (HH objects), located around 450 parsecs (about 1,470 light-years) away in a Bok globule near the Gum nebula. Astrophysical jet, Jets of partially ionized gas emerging from a Protostar, young star produce visible shocks upon impact with the Interstellar medium, ambient medium. Discovered in 1977, it is one of the most studied HH objects and the first jet to be associated with young stars was found in HH 46/47. Four emission nebulae, HH 46, HH 47A, HH 47C and HH 47D and a jet, HH 47B, have been identified in the complex. It also contains a mostly unipolar molecular outflow, and two large Bow shock (aerodynamics), bow shocks on opposite sides of the source star. The overall size of the complex is about 3 parsecs (10 light years). History of observations This object was discovered in 1977 by American astronomer, R. D. Schwartz. In accordance with the naming convention for HH objects, he named two nebulae he found HH 46 and HH 47, as the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pre-main-sequence Star
A pre-main-sequence star (also known as a PMS star and PMS object) is a star in the stage when it has not yet reached the main sequence. Earlier in its life, the object is a protostar that grows by acquiring mass from its surrounding envelope of interstellar dust and gas. After the protostar blows away this envelope, it is optically visible, and appears on the stellar birthline in the Hertzsprung-Russell diagram. At this point, the star has acquired nearly all of its mass but has not yet started hydrogen burning (i.e. nuclear fusion of hydrogen). The star continues to contract, its internal temperature rising until it begins hydrogen burning on the zero age main sequence. This period of contraction is the pre-main sequence stage. An observed PMS object can either be a T Tauri star, if it has fewer than 2 solar masses (), or else a Herbig Ae/Be star, if it has 2 to 8 . Yet more massive stars have no pre-main-sequence stage because they contract too quickly as protostars. By t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Star
A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sky, night; their immense distances from Earth make them appear as fixed stars, fixed points of light. The most prominent stars have been categorised into constellations and asterism (astronomy), asterisms, and many of the brightest stars have proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. The observable universe contains an estimated to stars. Only about 4,000 of these stars are visible to the naked eye—all within the Milky Way galaxy. A star's life star formation, begins with the gravitational collapse of a gaseous nebula of material largely comprising hydrogen, helium, and traces of heavier elements. Its stellar mass, total mass mainly determines it ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RCW 38
__NOTOC__ RCW 38 is a star-forming region in the southern constellation of Vela (known as the Sails). It includes an embedded HII region and a super star cluster. This region is located at a distance of approximately from the Sun. This is the youngest super star cluster in the Milky Way galaxy, with age estimates ranging from 0.1 to 1.0 Myr. It has around 10,000 member stars. The cluster member stars are still enshrouded within the dark cloud in which they were born. The star cluster is surrounded by clouds of brightly glowing gas and includes many protostars. Observations by the Chandra X-ray Observatory have revealed more than 800 X-ray emitting young stellar objects in the cluster. 139 infrared sources have been identified as variable, of which 47% are candidate young stellar objects. Jets emerging from young protostars drive further star formation in the surrounding cloud. The cluster includes about 20 massive O-type stars concentrated in a volume a few parsecs across ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Accretion Disk
An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is most frequently a star. Friction, uneven irradiance, magnetohydrodynamic effects, and other forces induce instabilities causing orbiting material in the disk to spiral inward toward the central body. Gravitational and frictional forces compress and raise the temperature of the material, causing the emission of electromagnetic radiation. The frequency range of that radiation depends on the central object's mass. Accretion disks of young stars and protostars radiate in the infrared; those around neutron stars and black holes in the X-ray part of the spectrum. The study of oscillation modes in accretion disks is referred to as diskoseismology. Manifestations Accretion disks are a ubiquitous phenomenon in astrophysics; active galactic nuclei, protoplanetary disks, and gamma ray bursts all involve accretion disks. These di ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bok Globule
In astronomy, Bok globules are isolated and relatively small dark nebulae containing dense cosmic dust and gas from which star formation may take place. Bok globules are found within H II regions, and typically have a mass of about two to 50 solar masses contained within a region about a light year or so across (about ). They contain molecular hydrogen (H2), carbon oxides and helium, and around 1% (by mass) silicate dust. Bok globules most commonly result in the formation of double- or multiple-star systems. History Bok globules were first observed by astronomer Bart Bok in the 1940s. In an article published in 1947, he and Edith F. Reilly hypothesized that these clouds were "similar to insect's cocoons" that were undergoing gravitational collapse to form new stars, from which stars and star clusters were born. This hypothesis was difficult to verify due to the observational difficulties of establishing what was happening inside a dense dark cloud that obscured all visible ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Infrared
Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those of red light (the longest waves in the visible spectrum), so IR is invisible to the human eye. IR is generally (according to ISO, CIE) understood to include wavelengths from around to . IR is commonly divided between longer-wavelength thermal IR, emitted from terrestrial sources, and shorter-wavelength IR or near-IR, part of the solar spectrum. Longer IR wavelengths (30–100 μm) are sometimes included as part of the terahertz radiation band. Almost all black-body radiation from objects near room temperature is in the IR band. As a form of EMR, IR carries energy and momentum, exerts radiation pressure, and has properties corresponding to both those of a wave and of a particle, the photon. It was long known that fires e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Main Sequence
In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or dwarf stars, and positions of stars on and off the band are believed to indicate their physical properties, as well as their progress through several types of star life-cycles. These are the most numerous true stars in the universe and include the Sun. Color-magnitude plots are known as Hertzsprung–Russell diagrams after Ejnar Hertzsprung and Henry Norris Russell. After condensation and ignition of a star, it generates thermal energy in its dense stellar core, core region through nuclear fusion of hydrogen into helium. During this stage of the star's lifetime, it is located on the main sequence at a position determined primarily by its mass but also based on its chemical composition and age. The cores of main-sequence stars are in hydros ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
