# Tag Info

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The statement is wrong, though sort of true. Gravitational waves are exceedingly hard to create and significant energy is radiated as gravitational waves only for massive stars rotating rapidly at a short distance. In principle the Earth-Moon system radiates gravitational waves, but at such a ridiculously low intensity that it's fair to say it doesn't ...

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A star with a temperature of 50.000 °K would have to be much larger than our sun to sustain that rate of fusion, and our Earth as we know it would not exist. It would have to be much further out and it would be unlikely to form a similar atmosphere. There would probably be more ozone as a direct result of more UV to break stuff, though all emission at UVB ...

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The neutron star crust is separated into outer and inner regions. The outer is a crust of neutron-rich nuclei surrounded by degenerate electrons. The inner is similar, but the nuclei are even more neutron-rich and there are degenerate neutrons too. The (qualitative) answer to your question looks at the ratio of electrostatic (Coulomb) energy to the thermal ...

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I've taught a few classes on stellar evolution and stellar modelling, and here are some of the resources I've recommended there. These all lean on the theoretical stellar structure side, rather than observational characteristics of certain types of star and so on. Free lecture notes Onno Pols (Utrecht) Jørgen Christensen-Dalsgaard (Aarhus) Both these ...

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Speed of sound usually refers to the propagation velocity of a low amplitude vibration in a medium in equilibrium. A "sound" can travel far faster than the speed of sound if it is, for example, a shock wave

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it's likely that when you google the term in general, most pages treat about the "speed of sound" at the common human meaning (sound in air :-) ), while its generalization to all the various circumpstances of fluids in the universe might more often been spelt "sound speed". But here it's more linguistic than physics, and it wouldn't be physically incorrect ...

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Look at the "bar" region of, e.g., NGC1300 and wonder whether you are seeing a neutrino star. If so it could be of greater mass than the visible galaxy so accounting for the linear g:r relationship in the bar region. If it is a Fermi condensate it could have a "liquid" surface at the tip of the bar with a lesser density tapering off in the spiral arms ...

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You can get a rough idea from the virial theorem. This tells us that for a gravitationally bound system the kinetic energy $T$ and the potential energy $V$ are related by: $$2T = -V$$ or obviously: $$T = -\tfrac{1}{2}V$$ Suppose we start with our dust cloud particles at infinity with $T = V = 0$ and let the system collapse until the potential energy ...

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For a uniform, spherical distribution of mass (cloud of gas and dust) of radius $R$ and mass $M$ in absence of magnetic, radiation fields etc, we have $dm = 4\pi \rho r^2 dr$ and the potential energy of a spherical shell of inner radius $r$ and outer $r + d r$ is $dU = -G\frac{m(r)dm}{r}$, $m(r) = \frac{4}{3}\rho r^3$, and a simple integration yields, ...

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The answer lies in something called the virial theorem. You are correct, a cloud that is in equilibrium will have a relationship between the temperature and pressure in its interior and the gravitational "weight" pressing inwards. This relationship is encapsulated in the virial theorem, which says (ignoring complications like rotation and magnetic fields) ...

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The secret is to evacuate the heat, mainly by radiation. But for this you need dust or "metals", since H and He alone radiates very unefficiently. Paradoxically it is not so easy to collapse completely enough. ( BTW for dark mater there is no possible radiation to dissipate energy, which keeps it fuzzy and a lot less concentrated than ordinary mater.)

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As gas clouds collapse, they increase in internal energy (measured by temperature). This is part of what causes their pressure to increase. As they increase in temperature, though, they also increase the amount of radiation they emit. As they emit radiation, their internal energy decreases and thus their pressure also decreases, allowing for further ...

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Electron degeneracy does not lead to an infinitely hard equation of state. The Pauli exclusion principle does not say that two fermions cannot occupy the same space; it says they cannot occupy the same quantum state. What this means is that as you squish the electrons together they have to occupy higher and higher momentum states. It is this non-zero ...

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If you read further on stellar evolution, if the mass of the original star is large enough electron degeneracy is overcome and the star becomes a neutron star, stable because of neutron degeneracy. This degeneracy is due to the Pauli exclusion principle which does not allow fermions of the same mass and charge to be in a single quantum state. What happens ...

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Iron fusion can take place in stars - what you need is lots of iron and very high temperatures. These conditions exist in the cores of massive stars near the ends of their lives. For example alpha particles can fuse with an iron-56 nucleus to produce nickel-60 and then zinc-64; these reactions are barely endothermic. The problem is that there are competing ...

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