What must be in equilibrium for a star to form?

Answer 1

Two great cosmic forces conspire to create a star from gas. Gravity is one, and time is the other. With sufficient material (the gas - mostly hydrogen), and over a great length of time, gas will be attracted by other gas due to gravity. As more gathers, more gravity attracts even more gas. It is a self-generating event if enough gas is initially present, as would be in a stellar nursery. As the "critical mass" of material accretes, the gravity - now overwhelming - pulls everything in and compresses the heck out of it. This heats the gas. At sufficient temperature, about 10 million degrees Kelvin, the proton-proton reaction that is nuclear fusion begins, and the star "turns on" for the first time. Hydrogen is being turned into helium. The star's initial fuel load will determine its type and its eventual fate. You got a link if you want it.

Answer 2

Stars form by the gravitational collapse of interstellar gas. This gas in normally in the form of a molecular cloud which is about 75% Hydrogen, such as the Orion nebula. The process that triggers star formation is not well known but it might be supernova or the shocks form the formation of other stars.

As the cloud collapses a number of things happens, the cloud heats up due to the release of gravitational energy and the conservation of angular momentum ensures that the cloud forms a flatted disc - the accretion disk. The cloud has a large scale magnetic field which due to it's massive size has field lines that appear perpendicular to the disk. The hot material in the disk get thermally lifted into the field, this causes the field to become coiled like a spring. The material trapped within the field lines is accelerated out in the form of a bipolar jet (about 99% of the material that ends up in the disk will be ejected) , this imparts a negative torque on the disk allow the remaining accrerate onto the proto-star.

Inside the protostar the increased mass and gravitational energy heats the core. At some stage a brief phase of Lithium and deuterium fusion will occur but this is very brief. Once the core reaches 15million K nuclear fusion of hydrogen occurs (the exact details are mass dependent) and the star enters the main sequence - it becomes an adult. It's nebula is dispersed ,it's jets have previously ceased

Answer 3

When a protostar is formed from the gas in a nebula, it is the result of gravitational attraction. This attraction causes matter to clump together until enough mass has accumulated that it collapses in on itself and begins the process of fusion.

Answer 4

The short answer is ''running out of hydrogen''.

Most stars (like our Sun) are in the "hydrogen burning" phase of their life.

That is to say they are converting hydrogen into helium by nuclear fusion.

This releases a lot of energy.

The heat released by this reaction keeps the core (centre) of the Sun extremely hot.

This heat energy stops the Sun collapsing in on itself under gravity. It is the longest period of an active stars life.

When the star runs out of hydrogen to "burn" it stops generating heat. The core is no longer supported by the release of heat at its centre. It starts to collapse. This causes the core to get hotter. When it gets hot enough it will reaches a point where it is hot enough to "burn" helium to create heavier elements.

The core becomes stable again but at a much hotter temperature than during the hydrogen burning phase.

The rate of energy release is also slower than during the hydrogen burning phase. One of the effects of this change is that the outside of the star gets bigger and cooler. This is why we call it a Red Giant. Red because the surface is cooler so releases light predominantly in the red part of the spectrum, giant because its big.

It happens like this: Nebula-->Protostar-->Main Sequence Star-->Red Giant.

Answer 5

Stars are formed from massive gas clouds in space. The gravitational attraction between these gases causes them to slowly come together over time, and spin around each other, as time goes on they spin faster and faster and draw closer together becoming hotter and hotter until they reach the temperature at which nuclear fission can begin. Once the fission begins the star has formed and gives out light and heat.

Answer 6

Do you mean a nova? A Nebula is a large group of stars and dust in the sky. e.g. the Orion nebula.

An individual star would not ordinarily change into a nebula, but the Crab Nebula is one such, first seen on earth about 1054 CE.

But it had taken about 6500 years for the light to reach us. If your query was about nova or supernova, ask again.

Answer 7

Type your answer here... A molecular cloud, sometimes called a stellar nursery if star formation is occurring within, is a type of interstellar cloud whose density and size permits the formation of molecules, most commonly molecular hydrogen (H2).

Molecular hydrogen is difficult to detect by infrared and radio observations, so the molecule most often used to determine the presence of H2 is CO (carbon monoxide). The ratio between CO luminosity and H2 mass is thought to be constant, although there are reasons to doubt this assumption in observations of some other galaxies.[1]

Answer 8

Gravity pulls it in together. Pressure spreads it out.

Answer 9

Gas coalesces in a nebula to form a proto star by the force of gravity. It can take an extremely long time, but new stars are created all the time out of the remains of old ones.

Answer 10

The expanding force of nuclear fusion and the collapsing force of gravity.