A Protostar is an object that forms by contraction out of the gas of a giant molecular cloud in the interstellar medium. The protostellar phase is an early stage in the process of star formation. For a solar-mass star it lasts about 100,000 years. It starts with a core of increased density in a molecular cloud and ends with the formation of a T Tauri star, which then develops into a main-sequence. This is heralded by the T Tauri wind, a type of super solar wind that marks the change from the star accreting mass into radiating energy. Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. ... 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. ... 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 dark nebula is a large cloud which appears as star-poor regions where the dust of interstellar medium seems to be concentrated. ... The interstellar medium (or ISM) is the name astronomers give to the tenuous gas and dust that pervade interstellar space. ... 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. ... // The T Tauri wind — so named because of the young star currently in this stage — is a phenomenon indicative of the phase of stellar development between the accretion of material from the slowing rotating material of a solar nebula and the ignition of the Hydrogen that has agglomerated into the... The plasma in the solar wind meeting the heliopause The solar wind is a stream of charged particles (i. ...

Observations reveal that giant molecular clouds are approximately in a state of virial equilibrium—on the whole, the gravitational binding energy of the cloud is balanced by the kinetic energy of the cloud's constituent molecules. Any disturbance to the cloud may upset its state of equilibrium. Examples of disturbances are shock waves from supernovae; spiral density waves within galaxies and the close approach or collision of another cloud. Whatever the source of the disturbance, if it is sufficiently large it may cause the force due to gravity to become greater than the force due to thermal kinetic energy within a particular region of the cloud. In mechanics, the virial theorem provides a general equation relating the average total kinetic energy of a system with its average total potential energy , where angle brackets represent the average of the enclosed quantity. ... The gravitational binding energy of an object is the amount of energy required to accelerate every component of that object to the escape velocity of every other component. ... The cars of a roller coaster reach their maximum kinetic energy when at the bottom of their path. ... 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ... For other uses, see Supernova (disambiguation). ... Density wave theory or the Lin-Shu density wave theory is a theory proposed by C.C. Lin and Frank Shu in the mid-1960s to explain spiral arm structure of certain galaxies. ... For other uses, see Galaxy (disambiguation). ... The cars of a roller coaster reach their maximum kinetic energy when at the bottom of their path. ...

The British physicist Sir James Jeans considered the above phenomenon in detail. He was able to show that, under appropriate conditions, a cloud, or part of one, would start to contract as described above. He derived a formula for calculating the mass and size that a cloud would have to reach as a function of its density and temperature before gravitational contraction would begin. This critical mass is known as the Jeans mass. It is given by the following formula: Sir James Hopwood Jeans (born Ormskirk, September 11, 1877, died Dorking, September 16, 1946) was a British physicist, astronomer and mathematician who was the first to propose the theory of continuous creation of matter in the universe. ... For other uses, see Mass (disambiguation). ... For other uses, see Density (disambiguation). ... For other uses, see Temperature (disambiguation). ... The British physicist Sir James Jeans considered the process of gravitional collapse within a gaseous cloud. ...

where n is the particle number density, m is the mass of the 'average' gas particle in the cloud and T is the gas temperature.

Fragmentation

Stars are often found in groups known as clusters which appear to have formed at around the same time. This can be explained if it is assumed that as a cloud contracts it does not do so uniformly. In fact, as first pointed out by Richard Larson, the giant molecular clouds in which stars are formed are universally observed to have turbulent velocities imposed on all scales within the cloud. These turbulent velocities compress the gas in shocks, which generate filaments and clumpy structures within the giant molecular cloud over a wide range of sizes and densities. This process is referred to as turbulent fragmentation. Some clumpy structures will exceed their Jeans mass and become gravitationally unstable, and may again fragment to form a single or multiple star system. A dark nebula is a large cloud which appears as star-poor regions where the dust of interstellar medium seems to be concentrated. ... Turbulent flow around an obstacle; the flow further away is laminar Laminar and turbulent water flow over the hull of a submarine Turbulence creating a vortex on an airplane wing In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by low-momentum diffusion, high momentum convection, and... Introduction The shock wave is one of several different ways in which a gas in a supersonic flow can be compressed. ... A dark nebula is a large cloud which appears as star-poor regions where the dust of interstellar medium seems to be concentrated. ... The British physicist Sir James Jeans considered the process of gravitional collapse within a gaseous cloud. ...

Whatever the reason, the cloud breaks up into smaller, denser areas which may again break into still smaller areas - the outcome being a cluster of protostars. This certainly agrees with the observation that star clusters are common. This article or section does not cite its references or sources. ...

Heating due to gravitational energy

As the cloud continues to contract it begins to increase in temperature. This is not caused by nuclear reactions but by the conversion of gravitational energy to thermal kinetic energy. As a particle (atom or molecule) decreases its distance from the centre of the contracting fragment this will result in a decrease in its gravitational energy. The total energy of the particle must remain constant so the reduction in gravitational energy must be accompanied by an increase in the particle's kinetic energy. This can be expressed as an increase in the thermal kinetic energy, or temperature, of the cloud. The more the cloud contracts the more the temperature increases. The gravitational binding energy of an object is the amount of energy required to accelerate every component of that object to the escape velocity of every other component. ... For other uses, see Temperature (disambiguation). ...

Collisions between molecules often leave them in excited states which can emit radiation as those states decay. The radiation is often of a characteristic frequency. At these temperatures (10 to 20 kelvins) the radiation is in the microwave or infrared range of the spectrum. Most of this radiation will escape hence preventing the rapid rise in temperature of the cloud. For other uses, see Radiation (disambiguation). ... For other uses, see Kelvin (disambiguation). ... This article is about the type of Electromagnetic radiation. ... For other uses, see Infrared (disambiguation). ...

As the cloud contracts the number density of the molecules increases. This will eventually make it more difficult for the emitted radiation to escape. In effect, the gas becomes opaque to the radiation and the temperature within the cloud will begin to rise more rapidly.

The fact that the cloud becomes opaque to radiation in the infrared makes it difficult for us to observe directly what is happening. We must look to longer wavelength radio radiation which does escape even the densest clouds. In addition, theory and computer modelling are necessary to understand this phase.

As long as the surrounding matter is falling onto the central condensation, it is considered to be in protostar stage. When the surrounding gas/dust envelope disperses and accretion process stops, the star is considered as pre-main sequence star. In HR diagram then it appears to be on the stellar birthline. Pre-main sequence star is a star in the stage when it has not yet reached the main sequence. ... Hertzsprung-Russell diagram In stellar astronomy, the Hertzsprung-Russell diagram (usually referred to by the abbreviation H-R diagram) shows the mathematical relationship between absolute magnitude, luminosity, stellar classification, and surface temperature. ... Stellar birthline is a predicted line on HR diagram of initial stellar radii as a function of mass at the end of the initial phase of accretion on protostar. ...

History

The term "proto-star" appears to have been first used in print in 1889.

"A protostar acquiring two condensations will become a binary and be stable thereafter [..] Whether a binary or a single star results depends largely on the total angular momentum of the protostar" ^[1]

Notes

See also

• Herbig-Haro object
• Protoplanetary disc
• NGC 7538, home of the largest discovered protostar which is about 300 times the size of our Solar System.

Herbig-Haro object HH47, imaged by the Hubble Space Telescope. ... A protoplanetary disc (also protoplanetary disk, proplyd) is an accretion disc surrounding a T Tauri star. ... There are very few or no other articles that link to this one. ... This article is about the Solar System. ...

External links

• Planet-Forming Disks Might Put Brakes On Stars (SpaceDaily) Jul 25, 2006
• Planets could put the brakes on young stars Lucy Sherriff (The Register) Thursday 27th July 2006 13:02 GMT
• Why Fast-Spinning Young Stars Don't Fly Apart (SPACE.com) 24 July 2006 03:10 pm ET