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Bipolar Outflow
A bipolar outflow comprises two continuous flows of gas from the poles of a star. Bipolar outflows may be associated with protostars (young, forming stars), or with evolved post-AGB stars (often in the form of bipolar nebulae). Protostars In the case of a young star, the bipolar outflow is driven by a dense, collimated jet. These astrophysical jets are narrower than the outflow and very difficult to observe directly. However, supersonic shock fronts along the jet heat the gas in and around the jet to thousands of degrees. These pockets of hot gas radiate at infrared wavelengths and thus can be detected with telescopes like the United Kingdom Infrared Telescope (UKIRT). They often appear as discrete knots or arcs along the beam of the jet. They are usually called molecular bow shocks, since the knots are usually curved like the bow wave at the front of a ship. Occurrence Typically, molecular bow shocks are observed in ro-vibrational emission from hot molecular hydro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Boomerang HST Big
A boomerang () is a thrown tool typically constructed with airfoil sections and designed to spin about an axis perpendicular to the direction of its flight, designed to return to the thrower. The origin of the word is from Australian Aboriginal languages, an Aboriginal Australian language of the Sydney region. Its original meaning, which is preserved in official competitions, refer only to returning objects, not to throwing sticks, which were also used for hunting by various peoples both in Australia and around the world. However, the term "non-returning boomerang" is also in general use. Various forms of boomerang-like designs were traditionally and in some cases are still used by some groups of Aboriginal Australians for hunting. The tools were known by various names in the many Aboriginal languages prior to Colonisation of Australia, colonisation. The oldest surviving Aboriginal boomerang, now held in the South Australian Museum, was found in a peat bog in South Australia, d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Herbig–Haro Object
Herbig–Haro (HH) objects are bright patches of nebula, nebulosity associated with newborn stars. They are formed when narrow jets of partially plasma (physics), ionised gas ejected by stars collide with nearby clouds of gas and dust at several hundred kilometers per second. Herbig–Haro objects are commonly found in Star formation#Stellar nurseries, star-forming regions, and several are often seen around a single star, aligned with its axis of rotation, rotational axis. Most of them lie within about one parsec (3.26 light-years) of the source, although some have been observed several parsecs away. HH objects are transient phenomena that last around a few tens of thousands of years. They can change visibly over timescales of a few years as they move rapidly away from their parent star into the gas clouds of interstellar space (the interstellar medium or ISM). Hubble Space Telescope observations have revealed the complex evolution of HH objects over the period of a few years, as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bipolar Nebula
A bipolar nebula is a type of nebula characterized by two lobes either side of a central star. About 10–20% of planetary nebulae are bipolar. Formation Though the exact causes of this nebular structure are not known, it is often thought to imply the presence of a binary central star with a period of a few days to a few years. As one of the two stars expelled its outer layers, the other disrupted the outflow of material to form the bipolar shape. Examples * Homunculus Nebula around Eta Carinae * Hubble 5 * M2-9 – The M2-9, Wings of a Butterfly Nebula * OH231.8+4.2 – The Calabash Nebula or Rotten Egg Nebula * Mz3 (or Menzel 3) – The Mz 3, Ant Nebula * CRL 618 – The Westbrook Nebula * CRL 2688 – The Egg Nebula * HD 44179 – The Red Rectangle Nebula * MyCn18 – The Engraved Hourglass Nebula * – The Southern Crab Nebula * The Boomerang Nebula * NGC 2346 – Also known as the Butterfly Nebula * NGC 6302 – The Bug or Butterfly Nebula * KjPn 8 Nebula – The largest ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astrophysical Jet
An astrophysical jet is an astronomical phenomenon where outflows of ionised matter are emitted as extended beams along the axis of rotation. When this greatly accelerated matter in the beam approaches the speed of light, astrophysical jets become relativistic jets as they show effects from special relativity. The formation and powering of astrophysical jets are highly complex phenomena that are associated with many types of high-energy astronomical sources. They likely arise from dynamic interactions within accretion disks, whose active processes are commonly connected with compact central objects such as black holes, neutron stars or pulsars. One explanation is that tangled magnetic fields are organised to aim two diametrically opposing beams away from the central source by angles only several degrees wide Jets may also be influenced by a general relativity effect known as frame-dragging. Most of the largest and most active jets are created by supermassive black holes (SM ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Accretion Disc
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 disks ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parsec
The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (AU), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and is defined as the distance at which 1 AU subtended angle, subtends an angle of one arcsecond ( of a degree (angle), degree). The nearest star, Proxima Centauri, is about from the Sun: from that distance, the gap between the Earth and the Sun spans slightly less than one arcsecond. Most Naked-eye stars, stars visible to the naked eye are within a few hundred parsecs of the Sun, with the most distant at a few thousand parsecs, and the Andromeda Galaxy at over 700,000 parsecs. The word ''parsec'' is a shortened form of ''a distance corresponding to a parallax of one second'', coined by the British astronomer Herbert Hall Turner in 1913. The unit was introduced to simplify the calculation of astronomical distances from raw observational data. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Planetary Nebulae
A planetary nebula is a type of emission nebula consisting of an expanding, glowing shell of ionization, ionized gas ejected from red giant stars late in their lives. The term "planetary nebula" is a misnomer because they are unrelated to planets. The term originates from the planet-like round shape of these nebulae observed by astronomers through early telescopes. The first usage may have occurred during the 1780s with the English astronomer William Herschel who described these nebulae as resembling planets; however, as early as January 1779, the French astronomer Antoine Darquier de Pellepoix described in his observations of the Ring Nebula, "very dim but perfectly outlined; it is as large as Jupiter and resembles a fading planet". Though the modern interpretation is different, the old term is still used. All planetary nebulae form at the end of the life of a star of intermediate mass, about 1-8 solar masses. It is expected that the Sun will form a planetary nebula at the e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proto-planetary Nebulae
A protoplanetary nebula or preplanetary nebula (PPN, plural PPNe) is an astronomical object which is at the short-lived episode during a star's rapid evolution between the late asymptotic giant branch (LAGB) phase and the subsequent planetary nebula (PN) phase. A PPN emits strongly in infrared radiation, and is a kind of reflection nebula. It is the second-from-the-last high-luminosity evolution phase in the life cycle of intermediate-mass stars (1–8 ). Naming The name protoplanetary nebula is an unfortunate choice due to the possibility of confusion with the same term being sometimes employed when discussing the unrelated concept of protoplanetary disks. The name protoplanetary nebula is a consequence of the older term planetary nebula, which was chosen due to early astronomers looking through telescopes and finding a similarity in appearance of planetary nebula to the gas giants such as Neptune and Uranus. To avoid any possible confusion, suggested employing a new term ... [...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] |
Optical
Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviolet, and infrared light. Light is a type of electromagnetic radiation, and other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties. Most optical phenomena can be accounted for by using the classical electromagnetic description of light, however complete electromagnetic descriptions of light are often difficult to apply in practice. Practical optics is usually done using simplified models. The most common of these, geometric optics, treats light as a collection of rays that travel in straight lines and bend when they pass through or reflect from surfaces. Physical optics is a more comprehensive model of light, which includes wave effects such as diffraction and interference that can ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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] |
