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They are very sparse. Typical densities are in the range of 100 to 10,000 particles per $\textrm{cm}^3$. This is much more dense than the general interstellar medium (1 particle per $\textrm{cm}^3$), but much, much less dense than anything you are used to - air is around $10^{19}$ particles per $\textrm{cm}^3$. You would very easily see your own hand in a ...


7

There is a well known process for taking mass away from nebulae (star formation) but there are many processes for putting mass back into nebulae as well. Stellar winds (which are very strong for extremely young, old, or massive stars) and supernovae being the most prominent examples. Star formation is not a very efficient process, a lot of the mass of a ...


1

Well, the equatorial velocity of a neutron star isn't more than $9 \times 10^7 \text{ m/s}$, which gives a $\gamma$ factor of $\sim 1$ (it's actually $1.08$, but that doesn't make a large difference to time dilation effects). I'm not too clear about how exactly frame dragging works, but it seems like a small time dilation effect wouldn't have a significant ...


1

In my opinion that "collapsing nebula" image is somewhat misleading, because the trajectory of dust/gas particles would be (ignoring magnetic field) an orbit and not a free fall collapse. However collisions make particle change orbit, and the particles whose new orbits comes closer to the future sun experience more collisions (because of the higher density ...



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