Summary: Stars type in cold, thick regions of space called molecule clouds. When the pressure of gravity pulling in ~ above the cloud is better than the strength of internal pressure pushing out, the cloud collapses right into a protostar.

You are watching: Another name for the interstellar matter that will eventually form a star is

Sections:Where perform stars form?Why perform stars form?What slow the cloud collapse?Nuclear FusionMasses of child StarsRelated linksRelated Lessons:Astro-Chronology

Stars form in the densest areas of the interstellar medium, or ISM, referred to as molecular clouds. The ISM is the name provided to the gas and also dust that exists between the stars within a galaxy. The is 99% gas and also 1% dust, by mass.

Properties the ISM gas in our an ar of the Milky means Galaxy:70% hydrogen28% helium2% facets heavier 보다 helium
The Orion Nebula(click for more images)

Molecular clouds room perfect star-forming regions because the mix of these atoms into molecules is much much more likely in really dense regions.

This photo shows the Orion Nebula, an interstellar cloud in i m sorry star equipment - and possibly planets - are forming. Our own solar mechanism presumably developed as gravity caused the please of a similar big cloud the gas. The item of cloud that developed our Solar device is well-known as the solar nebula.Click the picture to the left come see an ext images of the Orion Nebula.

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A star creates when a molecule cloud collapses under its own gravity forming a thick core sustained by nuclear fusion. This happens only once the pressure of heaviness pulling in exceeds the external push that pressure. High-density molecular clouds have actually stronger pressures of heaviness pushing in, make it simpler to get rid of the full pressure in ~ the cloud.SHOW METHE MATH

Once started, the fallen of the solar nebula continues since the force that gravity exerted ~ above the cloud grows more powerful as the cloud shrinks in size. The universal law of gravitation is composed mathematically:


Fg is the force of gravitational attraction, M1 and M2 room the masses that the 2 objects, and also d is the distance in between their centers. The price G is well-known as the gravitational constant. Its value is G = 6.67 · 10-11kg·m2/s2.

Before its please began, the gas that consisted of the solar nebula was most likely spread the end over a approximately spherical an ar a couple of light-years in diameter. This gas was incredibly low in density and extremely cold.

Possible reasons for the begin of a collapse:Shock wave from a adjacent exploding starCollision that 2 molecule clouds
The Crab Nebula(click to enlarge)

This is a snapshot of the Crab Nebula taken v the Hubble room Telescope. The Crab Nebula was produced when a star exploded. Ours Solar system is assumed to have created from particles expelled indigenous a supernova explosion over 4 billion year ago.


As the solar nebula shrinks in size, its density, temperature and also shape all undergo dramatic changes.

HEATING: The temperature that the solar nebula increases as the collapses. Together the cloud shrinks, the gravitational potential energy is converted to the kinetic power of individual gas particles falling inward. These particles crash into one another, converting their kinetic energy into heat energy.

SPINNING: choose an ice ska pulling in she arms together she spins, the solar nebula rotates faster and faster as it shrinks in radius. This boost in rotation price represents preservation of angular momentum. The rotation the the cloud may have been imperceptibly slow before its collapse began, but the cloud"s shrinkage makes rapid rotation inevitable.SHOW METHE MATH

FLATTENING: The solar nebula has flattened right into a disk. This flattening is a natural repercussion of collisions between particles in a turn cloud. A cloud might start with any type of size or shape, and also different clumps the gas in ~ the cloud might be moving in random directions at arbitrarily speeds. When the cloud collapses, these different clumps collide and also merge, leading to a planarization rotating disk.

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As the collapse continues, density increases and the molecule inside begin to interact more and more. This extra interaction reasons the temperature to increase. Due to the fact that pressure depends on density and also temperature (see present ME THE MATH), the pressure increases.SHOW METHE MATHOnce the pressure gets high enough, it begins to rival the strength of gravity and the fallen of the cloud slow down. Eventually, the cloud that gas i do not care a protostar: an child star that has actually not yet begun to fuse hydrogen in that core.

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Equilibrium of the Sun(click come enlarge)

A protostar is not considered a star until it gets its energy from nuclear combination instead the gravitational contraction. Gravitational contraction is the process of a cloud"s heaviness overcoming its internal pressure and causing a collapse. The main point temperature of an object must with a minimum temperature prior to the atom inside will fuse.

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Minimum temperature for:Hydrogen come fuse into helium: 10 million °Kelvin3 helium nuclei to fuse right into carbon: 100 million °Kelvin

The price of fusion increases until the lot of energy created in the core amounts to the amount of energy radiated native the surface. The perfect balance between energy produced and energy released stop the protostar indigenous collapsing further.

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Demographics the a 1-solar-mass Star(click to enlarge)
The number of low-mass stars is much greater than the variety of high-mass stars. Minimum mass of child star: 0.08 time the massive of the SunMaximum mass of newborn star: 150 times the fixed of the Sun

The diagram mirrors the relative number of stars because that every high-mass star. Because that every star 10-150 times the fixed of our Sun, there space 50 stars close to the fixed of our Sun. Our sunlight is pretty typical in size and also mass.

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