Star Formation

Interstellar medium Molecular cloud Bok globule | Dark nebula Young stellar object Protostar T Tauri star Herbig Ae/Be stars Nebular hypothesis

Classes of Object

Herbig-Haro object

Theoretical Concepts

Initial mass function Jeans Instability Kelvin-Helmholtz mechanism

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Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process and the study of early type stars and planet formation as its immediate products. Star formation theory, as well as accounting for the formation of a single star, must also account for the statistics of binary stars and the initial mass function. Media:Example. ... Image File history File links Download high-resolution version (1280x657, 174 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Star formation Protostar Template:Star Formation ... The interstellar medium (or ISM) is the name astronomers give to the tenuous gas and dust that pervade interstellar space. ... A molecular cloud is a type of interstellar cloud whose density and size permits the formation of molecules, most commonly molecular hydrogen (H2). ... An image of Bok globules in the H II region IC 2944, taken with the WFPC2 instrument on the Hubble Space Telescope A Bok globule is a dark cloud of dense dust and gas in which star formation is sometimes taking place. ... Dark Nebula Dark Nebula (Dark Zero in the original Japanese version) is a fictional character in the Kirby series of video games for Nintendo. ... Young stellar object (YSO) denotes a star in its early stage of evolution. ... A Protostar is an object that forms by contraction out of the gas of a giant molecular cloud in the interstellar medium. ... Drawing of a T-Tauri star with a circumstellar accretion disk T Tauri stars are a class of variable stars named after their prototype - T Tauri. ... Herbig Ae/Be stars are pre-main sequence stars - young (<10Myr) stars of spectral types A and B. They are still embedded in the gas-dust envelopes and may be surrounded by circumstellar disks. ... A planetary disk forming in the Orion Nebula In this artists conception, of a planet spins through a clearing in a nearby stars dusty, planet-forming disc In cosmogony, the nebular hypothesis is the currently accepted argument about how Earths Solar System formed. ... Herbig-Haro object HH47, imaged by the Hubble Space Telescope. ... The initial mass function (IMF) is a relationship that specifies the mass distribution of a newly formed stellar population, by giving the number of stars of mass per pc3 and per unit mass. ... It has been suggested that Jeans mass be merged into this article or section. ... The Kelvin-Helmholtz mechanism is an astronomical event that occurs when the surface of a star or a planet cools. ... A molecular cloud is a type of interstellar cloud whose density and size permits the formation of molecules, most commonly molecular hydrogen (H2). ... For other uses, see Plasma. ... STAR is an acronym for: Organizations Society of Ticket Agents and Retailers], the self-regulatory body for the entertainment ticket industry in the UK. Society for Telescopy, Astronomy, and Radio, a non-profit New Jersey astronomy club. ... For other uses, see Astronomy (disambiguation). ... The interstellar medium (or ISM) is the name astronomers give to the tenuous gas and dust that pervade interstellar space. ... A dark nebula is a large cloud which appears as star-poor regions where the dust of interstellar medium seems to be concentrated. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. ... The accretion theory, in astrophysics, is a scientific theory of the formation of our Solar system. ... For the band of the same name, see: Binary Star (band) Hubble image of the Sirius binary system, in which Sirius B can be clearly distinguished (lower left). ... The initial mass function (IMF) is a relationship that specifies the mass distribution of a newly formed stellar population, by giving the number of stars of mass per pc3 and per unit mass. ...

Theoretical Outline

According to current theories of star formation, cores of molecular clouds (regions of especially high density) become gravitationally unstable, fragment, and begin to collapse (the so-called spontaneous star formation), or shockwaves from supernovae or other energetic astronomical processes trigger star formation in nearby nebulae (the so-called triggered star formation). Part of the gravitational energy lost in this collapse is radiated in the infrared, with the remainder increasing the temperature of the core of the object. The accretion of material happens partially through a circumstellar disc. When the density and temperature are high enough, deuterium fusion ignition occurs, and the outward pressure of the resultant radiation slows (but does not stop) the collapse. Material comprising the cloud continues to "rain" onto the protostar. In this stage bipolar flows are produced, probably an effect of the angular momentum of the infalling material. Finally, hydrogen begins to fuse in the core of the star, and the rest of the enveloping material is cleared away. This article or section does not cite its references or sources. ... Multiwavelength X-ray image of the remnant of Keplers Supernova, SN 1604. ... For other uses, see Infrared (disambiguation). ... A proplyd in the Orion Nebula. ... Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance in the oceans of Earth of approximately one atom in 6500 of hydrogen (~154 PPM). ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. ... A Protostar is an object that forms by contraction out of the gas of a giant molecular cloud in the interstellar medium. ... This gyroscope remains upright while spinning due to its angular momentum. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ...

The protostar follows a Hayashi track on the Hertzsprung-Russell diagram.^[1] The contraction will proceed until the Hayashi limit is reached, and thereafter contraction will continue on a Kelvin-Helmholtz timescale with the temperature remaining stable. Stars with less than 0.5 solar masses thereafter join the main sequence. For more massive protostars, at the end of the Hayashi track they will slowly collapse in near hydrostatic equilibrium, following the Henyey track.^[2] The Hayashi track is a path taken by protostars in the Hertzsprung-Russell diagram after the protostellar cloud has reached approximate hydrostatic equilibrium. ... The Kelvin-Helmholtz mechanism is an astronomical event that occurs when the surface of a star or a planet cools. ... The Henyey track is a path taken by protostars with masses >0. ...

The stages of the process are well defined in stars with masses around one solar mass or less. In high mass stars, the length of the star formation process is comparable to the other timescales of their evolution, much shorter, and the process is not so well defined. The later evolution of stars are studied in stellar evolution. In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... In astronomy, stellar evolution is the sequence of radical changes that a star undergoes during its lifetime (the time in which it emits light and heat). ...

Observations

The Orion Nebula is a picture book of star formation, from the massive, young stars that are shaping the nebula to the pillars of dense gas that may be the homes of budding stars. This turbulent star formation region is one of astronomy's most dramatic and photogenic celestial objects.

Key elements of star formation are only available by observing in wavelengths other than the optical. The structure of the molecular cloud and the effects of the protostar can be observed in near-IR extinction maps (where the number of stars are counted per unit area and compared to a nearby zero extinction area of sky), continuum dust emission and rotational transitions of CO and other molecules; these last two are observed in the millimeter and submillimeter range. The radiation from the protostar and early star has to be observed in infrared astronomy wavelengths, the extinction caused by the rest of the cloud where it is being formed is usually too big to allow us to observe it in the visual part of the spectrum. This presents considerable difficulties as the atmosphere is almost entirely opaque from 20um to 850um, with narrow windows at 200 and 450um. Even outside this range atmospheric subtraction techniques must be used. Image File history File links Download high-resolution version (18000x18000, 18853 KB)Do not load this image in your browser; it is too large and may cause your browser to hang. ... Image File history File links Download high-resolution version (18000x18000, 18853 KB)Do not load this image in your browser; it is too large and may cause your browser to hang. ... The Orion Nebula (also known as Messier 42, M42, or NGC 1976) is a diffuse nebula situated south of Orions Belt. ... The wavelength is the distance between repeating units of a wave pattern. ... Optical astronomy encompasses a wide variety of observations via telescopes that are sensitive in the range of visible light. ... A rotational transition is an abrupt change in angular momentum in quantum physics. ... Carbon monoxide, with the chemical formula CO, is a colorless, odorless, and tasteless gas. ... The Very Large Array, a radio interferometer in New Mexico, USA Radio astronomy is a subfield of astronomy that studies celestial objects in the radio frequency portion of the electromagnetic spectrum. ... For other uses, see Infrared (disambiguation). ... Extinction is a term used in astronomy to describe the absorption of light from astronomical objects by matter between them and the observer. ...

The formation of individual stars can only be directly observed in our Galaxy, but in distant galaxies star formation has been detected through its unique spectral signature. For other uses, see Milky Way (disambiguation). ... Gas chromatography-mass spectrometry (GC-MS) is a method that combines the features of gas-liquid chromatography and mass spectrometry to identify different substances within a test sample. ...

Notable Pathfinder Objects

• MWC 349 was first discovered in 1978, and is estimated to be only 1,000 years old. Since the object is located at a distance of 10,000 lightyears, it actually is now 11,000 years old.
• VLA 1623 -- The first exemplar Class 0 protostar, a type of embedded protostar that has yet to accrete the majority of its mass. Found in 1993, is possibly younger than 10,000 years [1].
• L1014 -- An incredibly faint embedded object representative of a new class of sources that are only now being detected with the newest telescopes. Their status is still undetermined, they could be the youngest low-mass Class 0 protostars yet seen or even very low-mass evolved objects (like a brown dwarf or even an Interstellar planet). [2].
• IRS 8* -- The youngest known main sequence star, discovered in August 2006. It is estimated to be 3.5 million years old [3].

Light year, a measure of distant Lightyear (band), a ska-punk band from the UK Buzz Lightyear, a character in the animated film Toy Story. ... This brown dwarf (smaller object) orbits the star Gliese 229, which is located in the constellation Lepus about 19 light years from Earth. ... An interstellar planet is a hypothetical type of rogue planet that has been ejected from its solar system by a proto-gas giant to become an outcast, drifting in interstellar space. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ...

Low Mass and High Mass Star Formation

Stars of different masses are thought to form by slightly different mechanisms. The theory of low-mass star formation, which is well-supported by a plethora of observations, suggests that low-mass stars form by the gravitational collapse of rotating density enhancements within molecular clouds. As described above, the collapse of a rotating cloud of gas and dust leads to the formation of an accretion disk through which matter is channeled onto a central protostar. For stars with masses higher than about 8 solar masses, however, the mechanism of star formation is not well understood.

Massive stars emit copious quantities of radiation which pushes against infalling material. In the past, it was thought that this radiation pressure might be substantial enough to halt accretion onto the massive protostar and prevent the formation of stars with masses more than a few tens of solar masses. Recent theoretical work has shown that the production of a jet and outflow clears a cavity through which much of the radiation from a massive protostar can escape without hindering accretion through the disk and onto the protostar. Present thinking is that massive stars may therefore be able to form by a mechanism similar to that by which low mass stars form. Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. ...

There is mounting evidence that at least some massive protostars are indeed surrounded by accretion disks. Several other theories of massive star formation remain to be tested observationally. Of these, perhaps the most prominent is the theory of competitive accretion, which suggests that massive protostars are "seeded" by low-mass protostars which compete with other protostars to draw in matter from the entire parent molecular cloud, instead of simply from a small local region. Another theory of massive star formation suggests that massive stars may form by the coalescence of two or more stars of lower mass.

References

1. ^ C. Hayashi (1961). "Stellar evolution in early phases of gravitational contraction". Publications of the Astronomical Society of Japan 13: 450-452. 
2. ^ L. G. Henyey, R. Lelevier, R. D. Levée (1955). "The Early Phases of Stellar Evolution". Publications of the Astronomical Society of the Pacific 67 (396): 154. 

External links

• Star formation