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10km is about right, 5km is definitely wrong. The Schwarzschild radius, inside which an object would be a black hole, is $3(M/M_{\odot})$ km. As neutron stars have a typical mass of $1.5M_{\odot}$ then a 5km radius would have them hovering just above disappearing inside their event horizons. Now you might have thought that this was possible given a "hard" ...


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A few clarifications on this thread in case anyone is reading in the future and is getting confused. I know however, that the temperature did in fact change, hence it's not an adiabatic process. That isn't really how an adiabatic process is defined. The temperature can change within a system (and often does) and it still be adiabatic. An adiabatic ...


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Most of the books which I looked at give approximately 10 km as the radius of a neutron star. Just yesterday I looked at a book by Dave Goldberg titled The Universe In the Rearview Mirror (2013) which says that they're "only about 5 km in radius" [p.225]. Is this true, [i.e., is there some recent evidence for this], or did he make a mistake here? These are ...


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I provide below a rough guess of what might be influenced or influence it, and possible cosmological effects. It is by no means an answer you can take to the bank. But it is based on some of the relevant physics. I'm probably missing other relevant issues, and I hope others chime in, if only as an exercise in non-factual what ifs. It's pretty hypothetical ...


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The equations for the density of air are available on the engineering toolbox site. The density of dry air is approximately given by: $$ \rho_{dry} = \frac{0.0035\,P_0}{T} $$ where $P_0$ is the pressure and $T$ is the temperature. The density of moist air is approaximately given by: $$ \rho_{wet} = \rho_{dry}\,\frac{1 + x}{1 + 1.609 x} $$ where $x$ is ...


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It's because the centre of buoyancy and centre of gravity don't necessarily lie on the same point. This creates two types of mechanical equilibrium: stable and unstable. It turns out that when a human body is floating with its face inside the water, the body is in stable equilibrium. That is because in that position, the centre of gravity lies below centre ...


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Turns out it's more of a bio question. https://www.google.com/search?q=why+do+dead+people+float&oq=why+do+dead+people+float&aqs=chrome..69i57.6523j0j1&sourceid=chrome&ie=UTF-8 As for the head part, your head (mainly your brain) is more dense than water.


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If I understand you correctly you are concerned that a black hole somehow manages to become less dense than the matter that made it, as if it somehow expands against its own gravity to increase its volume. However a black hole event horizon is not an object - it is just a place in spacetime. Although we can calculate a density by calculating the volume ...


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There is nothing wrong in having something more dense than a black hole, large black holes can have densities less than water. If you put a lot of iron together it might or not become a black hole. An object of any density can be large enough to fall within its own Schwarzschild radius. The larger the black hole the lower the density, so you iron ball will ...


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The density of water (and other fluids) depends both on the pressure and the temperature. A graph for water is here: You may see that at 1 bar (1 atmosphere), the density is highest around 4 °C. That's the conditions where the density reaches the nice 1,000 kilograms per cubic meter. Water contracts when it gets warmer than that, but also when it gets ...



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