The Gravo-Thermal Catastrophe

Post by hoseja » Mon, Sep 23, 2024, 10:53 AM UTC

kazinator wrote: post #29

Something doesn't add up, obviously. For one thing, squeezing the sphere smaller against pressure requires work . That's an external energy input. The system is not closed if some agent is available that can squeeze the sphere smaller.

Post by hnuser123456 » Mon, Sep 23, 2024, 3:54 PM UTC

pavel_lishin wrote: post #9

jessriedel wrote: post #8

Is this right?: * Although you can make the enveloping sphere as large as you want, the (anti-)equilibration process requires a sphere of some finite radius because if you wait long enough a few stars eventually get launched at escape velocity, and if these actually escaped they would effectively cool the remaining stars. * Therefore, the characteristic time scale for this process (i.e., the timescale on which the av…

> In real life, these turn into black holes I think this is right, and I think he explicitly calls out that these calculations were done with Newtonian physics modeling point particles - and we know that those two factors severely limit the application of this to the real-world.

Post by kazinator » Mon, Sep 23, 2024, 7:06 PM UTC

hoseja wrote: post #31

kazinator wrote: post #29

Something doesn't add up, obviously. For one thing, squeezing the sphere smaller against pressure requires work . That's an external energy input. The system is not closed if some agent is available that can squeeze the sphere smaller.

It's not getting squeezed, it's just gravitationally collapsing. The same thing happens when forming stars, except obviously there's all the electromagnetic repulsion, then nuclear repulsion, then black hole formation. The article speaking about "stars" as analogy for pointlike masses is kinda misleading. If it talked instead about gas in a nebula forming into a hot star, it would make much more sense.