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The formation of stars begins with the collapse and fragmentation of molecular clouds into very dense clumps. These clumps initially contain ~0.01 solar masses of material, but increase in mass as surrounding material is accumulated through accretion.

Protostar cloud
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A protostar cloud is a stellar formation of several protostars.

Wikipedia, the free encyclopedia - Cite This Source
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.

A protostar is a cloud of hot, dense gas and dust that is gravitationally collapsing to form a star.
A pulsar is a rapidly spinning neutron star that emits energy in pulses.

Protostars and Planets IV (V. Manings Ed.)

~s form when sections of giant molecular clouds start to collapse. Clouds are initially diffuse enough that they do not contract unless something triggers an increase in the density of some regions within a cloud. There are several possible causes that include: ...

A star in its earliest stages of formation.
A pulsating radio source thought to be associated with a rapidly rotating neutron star.

The initial stage of stellar formation. A ~ generates energy but its core is not hot enough to ignite nuclear fusion.

Very dense regions (or cores) of molecular clouds where stars are in the process of forming.

A collapsing cloud of gas and dust destined to become a star.
Pulsar ...

~: A star in the process of formation which has not yet become hot enough in the core to initiate the process of nuclear fusion (107 K) to halt its gravitational collapse.

A star in the process of being born from an interstellar gas cloud.

A protostar is a star that is still forming and nuclear fusion has not yet begun.

~- a stage in the formation of a star which implies the body is nearly full-size; the star is still within its parent nebula, and does not yet produce energy through nuclear fusion
Pulsar- collapsed star composed mainly of neutrons; pulsars are young, fast-spinning neutron stars ...

The contracting cloud heats up due to friction and forms a glowing protostar; this stage lasts for roughly 50 million years. If there is enough material in the protostar, the gravitational collapse and the heating continue.

~s with masses less than roughly 0.08 M⊙ (1.6-1029 kg) never reach temperatures high enough for nuclear fusion of hydrogen to begin. These are known as brown dwarfs.

~ Astronomy Products
Maker of a high quality line of diagonal mount assemblies and secondary mirrors for use in small, medium, and large amateur telescopes.

~ Stage in star formation when the interior of a collapsing cloud of gas is sufficiently hot and dense that it becomes opaque to its own radiation, but not hot enough for the onset of nuclear reactions. [More Info: Field Guide] ...

A collection of interstellar gas and dust whose gravitational pull is causing it to collapse on itself and form a star.
Pulsar ...

~s often exhibit strong winds. Radio and infrared observations of hydrogen and carbon monoxide molecules, again in the Orion cloud, have revealed gas expanding outward at velocities approaching 100 km/s.

~: A forming star, prior to settling down to the main sequence and burning hydrogen in its core.

A ~ will reach a temperature of 2000 to 3000 K, hot enough to glow a dull red with most of its energy in the infrared. The cocoon of gas and dust surrounding them blocks the visible light.

1. ~
The initial collapse occurs quickly, over a period of a few years. As the star heats up, pressure builds up following the Perfect Gas Law:
PV = NRT ...

The ~, embedded within a cloud of gas and dust known as RCM 120, is destined to evolve into one of the biggest and brightest stars in our Galaxy within the next few hundred thousand years.

The ~, located in the Perseus Spiral Arm of the Milky Way Galaxy, is 300 times the size of the solar system.
NGC 188 (Caldwell 1) ...

The ~ "bits" are all destined to become individual stars of assorted mass. Less massive lumps become low mass stars while massive lumps become high mass stars. As a general rule there are lots of low mass stars for every high mass star.

Each protostar collapses very quickly; its gas falls inward in free fall. A protostar can collapse from a size equal to the outer diameter of the solar system to about 30 times the Sun's size (the size of Mercury's orbit) in about six months.

In some protostars, contraction remains the only source of energy; these are brown dwarfs, and they die away slowly, over hundreds of billions of years.

This is known as a protostar. At this stage the temperature is still too low for nuclear fusion to happen. If the mass is too low, the failed star ends up as a brown dwarf. Some astronomers consider Jupiter to be a failed star.

The light from a protostar is absorbed by the dust surrounding it, causing the dust to warm up and radiate in the infrared. Infrared studies of star forming regions give us important information about how stars are born, and thus, on how our own Sun and solar system were formed.

T TAURI STAR - Protostar in the late stages of formation, often exhibiting both periodic and random fluctuations in brightness. T Tauri stars are newly-formed (<10 Ma) low to intermediate mass stars (< 3 Msun) with central temperatures too low for nuclear fusion to have started.

The cloud of gas and dust around a contracting ~ that conceals it at visible wavelengths.
Collisional Broadening
The smearing out of a spectrum line because of collisions among the atoms of the gas.
Color Index
A numerical measure of the color of a star.
Comet ...

The tremendous heat given off by the nuclear fusion process causes the gas to glow creating a ~. This is the first step in the evolution of a star. The glowing ~ continues to accumulate mass.

After the central ~ collapses to a sphere, gas continues to fall onto it from the nebula, via the accretion disk.

No, as you'll learn, Red Giants are stars near the end of their lives, while these ~s haven't even ripened (haven't "turned on" yet).

This cycle continues and just like a haystack in summer the inside of the ~ starts to get very hot. If enough material is is hoovered up from the surrounding gas and dust, the ~ will hit a critical point in its life.

Dense "clumps" of dust circle variable ~ R Monocerotis (at the tip of nebula) and cast dark shadows on the walls of a cavity etched by the ~'s light in a dark molecular cloud (inside which this ~ formed).

How stars evolve through each stage of their life cycle, from ~ to white dwarf or supernova, and examples of stars at each stage you can easily see with your own eyes ...

This theory is a version of Jeans's theory in which the Sun interacts with a nearby ~ dragging a filament of material from the ~.

The center compresses enough to become a ~ and the rest of the gas orbits/flows around it. Most of that gas flows inward and adds to the mass of the forming star, but the gas is rotating. The centrifugal force from that prevents some of the gas from reaching the forming star.

Diffuse material orbiting around a central body such as a ~, a young star, a neutron star or a black hole.

When a star is growing, as the ~ gains mass, the radiation pressure increases and pushes matter out, making it harder and harder to accumulate more mass. Anything that tries to fall onto the ~ gets blown off again. So, the star can't grow any more massive.

Within 50 million years, the pressure and density of hydrogen in the centre of the ~ became great enough for it to begin thermonuclear fusion.

A cool ( 20 µ, and a CO cloud is centered on it. It is probably a collapsing cloud of 102-103 M in which ~s are embedded. (KL nebula) [H76]
A type of electron tube used in radar and high-frequency radio work. [H76]
knock-on spectrum ...

This is another emission nebula, with young hot ~s that can be observed only in infrared wavelengths. It is nearly as bright as M21, and stretches nearly three quarters of a degree across the sky. It is just four degrees south of southeast and 21 degrees above the horizon at 10 p.m.

Hayashi contraction is a gravitational phemonenon in which a ~ becomes smaller, coalescing into a main sequence star.

" (T Tauri and its kind are "~s" that are still in the act of formation, are still accreting matter from their surrounding disks, which will most likely spawn planets, and have yet to turn on their hydrogen fusion; see the region of T Tauri on the Anticenter page.) As a G8 dwarf, Iota Lep B, ...

Narrow, high-energy streams of gas and other particles generally ejected in two opposite directions from some central source. Jets appear to originate in the vicinity of an extremely dense object, such as a black hole, pulsar, or ~, with a surrounding accretion disk.

Eventually, the central ~ becomes so hot and compressed that nuclear fusion begins at the core, this makes more material and the disk to be blown off, and the starts to shine into clear space.

Known as a ~, it is this hot core at the heart of the collapsing cloud that will one day become a star.

granule (solar) small, roundish patch of dark nebulosity that may be the precursor of a ~. grating optical surface (transmissive or reflective) upon which is ruled a large number of finely spaced grooves.

See also: See also: What is the meaning of Star, Astro, Solar, Nebula, Planet?

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