# Forming a Star: What Drives Gas & Dust Clusters?

• JayKo

#### JayKo

star is created from a cluster of gas. but how is this process take place? in the sense that what is driving the gas and dust to form a star? as only massive object can experience gravity. only after a star is formed, then gravity will come into play. but my question is? before gravity come into play, what causes a gas and dust to form as a star? thanks.

Our current idea is that passing clumps of gas manipulate the each other with their gravity, therefore causing some areas in the gas to clump up on teh side nearest the passing clouds, this then keeps on collapsing to form a star.

Every object with mass experiences gravity and exerts gravity on other objects.

Every object with mass experiences gravity and exerts gravity on other objects.

but only massive object feels gravity. gas and dust is too small to exert gravity to others and feel gravity from other objects.

but only massive object feels gravity. gas and dust is too small to exert gravity to others and feel gravity from other objects.

This is not true. You are under a misapprehension.

A volume of gas and dust of mass m will have exactly the same gravitational pull as a rocky body of mass m.

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Our current idea is that passing clumps of gas manipulate the each other with their gravity, therefore causing some areas in the gas to clump up on teh side nearest the passing clouds, this then keeps on collapsing to form a star.

what is the critical mass of the gas clouds in order for this to happen?

Each little bit piles up into a bigger bit, and it just snowballs from there.

This is not true.

The gravitational constant is a small number!. if the mass is small, the force it feels is small.

Each little bit piles up into a bigger bit, and it just snowballs from there.

what attract the small pieces to the ball of gas and dusts

If a cloud of dust exceeds the Jean's mass, it will eventually collapse to form a star (or dwarf star, depending).

The gravitational constant is a small number!. if the mass is small, the force it feels is small.

what attract the small pieces to the ball of gas and dusts

Two microscopic particles have a gravitational force between them, even if it is very small. Clous of dust and gas though, are not merely discrete particles; they might mass as much as a whole solar system. So we're talking about each particle feeling the gravitational pull of an entire solar system's mass.

It might take a billion years for dust and gas to form a star, but it does happen.

We present 1.3 mm wavelength interferometric observations of externally irradiated young stellar objects (proplyds) embedded within the Orion Nebula, including the three largest circumstellar disks seen in silhouette against the background nebular light. One field is centered on the 2&arcsec; diameter edge-on disk 114-426. The second field is centered on the large teardrop-shaped object 182-413 (HST 10), which contains a very opaque 0&farcs;4 diameter edge-on disk. This field also contains four other proplyds, including the large pure silhouette 183-405 (HST 16). We derive upper bounds on the dust masses of these disks from the absence of continuum emission and upper bounds on the gas masses from the lack of CO emission. These limits imply circumstellar disk masses less than 0.015 M&sun; for the observed sources and upper bounds on the column density of 13CO of N(13CO) < 1.4 × 1015 cm-2 averaged over the synthesized beam. Comparison with lower bounds on the dust content derived from the visibility of the circumstellar material in silhouette against the background nebular light and the extinction toward the embedded central star implies that 13CO may be less abundant in these circumstellar environments than in normal molecular clouds. The nondetection statistics are combined with estimates of radiation-induced mass-loss rates to derive an upper bound on the UV irradiation time for these young stellar objects. The young stellar objects in the Orion Nebula that are still surrounded by circumstellar material have been exposed to external UV radiation for less than 105 yr and possibly for as little as 104 yr.

http://iopscience.iop.org/1538-3881/116/2/854/fulltext?ejredirect=migration"

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Two microscopic particles have a gravitational force between them, even if it is very small. Clous of dust and gas though, are not merely discrete particles; they might mass as much as a whole solar system. So we're talking about each particle feeling the gravitational pull of an entire solar system's mass.

It might take a billion years for dust and gas to form a star, but it does happen.

thanks, i understand it better now.

this is a little bit deep

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The additional gravity of dark matter also aided in star formation. Massive clouds of DM formed before the stars and acted as gravity wells to collect the gas and dust into stellar nurseries. Supernovae within these nurseries created shockwaves that further drove the particles together.

The additional gravity of dark matter also aided in star formation. Massive clouds of DM formed before the stars and acted as gravity wells to collect the gas and dust into stellar nurseries. Supernovae within these nurseries created shockwaves that further drove the particles together.

ok, this is something new to me, all this while, has been taught that only gravity play the role.

The gravitational constant is a small number!. if the mass is small, the force it feels is small.
The mass of a cloud of hydrogen is the same as (or larger than) the mass of the star created from it. Therefore the gravitational field strength is the same (or larger).

Don't think of a star as one single object, it is a collection of individual hydrogen atoms. And a cloud of hydrogen, before collapes, is the same collection of individual hydrogen atoms - just further apart. So as long as the gravitational force pulling these particles toward the cloud's common center of mass is enough to overcome their own semi-random motion, it'll collapse.