# Tag Info

13

It's more do do with having a higher pressure gradient than a higher pressure, though for a cloud of a set size, the two are equivalent. For a cloud to be in equilibrium requires $$\frac{dP}{dr} = - G\frac{M\rho}{R^2},$$ where $dP/dr$ is the pressure gradient and $M$ and $R$ are the mass and radius of the cloud and $\rho$ is its density. It we just make a ...

9

I have mulled over this a couple of times (it's a really interesting question!), and hopefully come up with a somewhat enlightening answer. I haven't been able to find a good, modern reference for these details (perhaps I just suck at literature searches...) so there's a little mucking around in the history books The total timescale of evolution onto the ...

8

Stellar systems are born from clouds of turbulent gas. Although "turbulence" means that different parcels of gas move in different directions, the cloud have some overall, net angular momentum. Usually a cloud gives birth to multiple stellar systems, but even the subregion forming a given system has a net, and non-vanishing (i.e. $\ne0$), angular momentum. ...

6

The test to see whether degeneracy pressure is going to be significant is to compare $kT$ with the Fermi energy $E_F$ The Fermi energy is the energy level up to which all energy states would be occupied in a completely degenerate fermion gas. It is given by (for non-relativistic conditions) $$E_F = \frac{h^2}{2m}\left(\frac{3}{8\pi}\right)^{2/3} n^{2/3},$$...

6

Astronomers distinguish a prototstar from a star based on whether the object is visible. A protostar is hidden by the gas cloud that surrounds it. Protostars aren't visible. At some point in their evolution (and where this occurs depends on mass and metallicity), a protostar will start clearing the surrounding cloud of gas. This process happens very quickly ...

5

There are several misconceptions in your question. First, a star does not vacuum everything in its vicinity. Rather it forms from a condensation in a gas cloud, which in turn collapses to a proto-star surrounded by a gas disc, which can contribute further material. Once formed in this way, a star typically does not acquire more gas (exceptions are symbiotic ...

4

You could start from the premise that there was no net angular momentum in the universe at all; but it would still be the case that everything of interest was spinning. On the scales of stars and planets there are (at least) two important mechanisms that result in individual systems having angular momentum. The first is turbulence. If you take a parcel of ...

3

So then why would gas giant cores be electron degenerate, but not become hot enough for nuclear fusion? Degeneracy isn't an on/off switch. It's a quantum mechanical aspect of pressure that is always present, just as is thermal pressure. A substance is highly degenerate if degeneracy pressure completely dominates over thermal pressure, non-degenerate if ...

3

If you want to trigger outflows, there are two main processes that can help: magnetic field; radiation pressure. Magnetic fields is well-suited to launch such outflows, through magneto-centrifugal effects. Basically, if there is magnetic fields tighed to the disk surrounding the protostar and the angle between the field lines and the disk is right, a ...

2

First, thanks to @LCD3 for leading me on the right path here. My original answer was inaccurate, and so I got rid of it. A supernova occurs when a very massive star can no longer sustain enough nuclear fusion to combat the force of its own gravity pushing inwards on it. This happens after the star has gone through different stages of fusion. Typically, it ...

2

Our sun is a 3rd or 4th generation star, so yes, there is enough hydrogen left over to create more stars. We know this because our solar system is fairly rich in heavy elements, which means that there must have been at least 1, and probably 2 or 3 supernovas that created these heavier elements that created all of the rocky planets, asteroids, comets, etc. ...

2

Although pre-main sequence stars have lower temperature, they are essentially huge clouds of gas, often as large as 1 pc wide. The luminousity being proportional to square of the radius is essentially large for pre-main sequence stars. Plus, the problem with gravitational contraction is not the amount of energy that can be generated per second. That can ...

2

Well the spin of the accretion disc is relative. We consider the top of anything as North. What if the the top was to be the South. It depends on perspective. Something rotating clockwise when seen from north would rotate counter clockwise when seen from south.

2

At the end of the protostar phase a vigorous outflow from the star develops called the T-Tauri Wind and this could cut off accretion. Eventually, it develops into a normal star and the strong wind dies down. Material that was not totally blown away could then continue to fall down and be accreted

1

As an undergraduate, you are a member of a university. Your first step then should be to talk to your Professors. As a guide to what might be expected, look at the University of Arizona telescope proposal page They accept proposals from members of Arizona University. You have to have a clear aim and plan. This is why you need to talk to your professors ...

1

Any gaseous object has some spin, usually acquired by interactions with other objects. For example, (proto-)galaxies torque each other to acquire a low rate of angular momentum. Initially, this spin is rather low in the sense that it does not dominate the dynamics: the energy in rotational motion is small compared to other energies, typically by a factor \$\...

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