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arcanum7123 t1_jdvzdt1 wrote

Reply to comment by ThrowawayPhysicist1 in Black holes may be swallowing invisible matter that slows the movement of stars by trevor25

>This will mean it will probably never form a structure like a star but even if the densities got that high

Can you explain more about this? What's to stop it forming dark planets? (I understand they're being no stars under the assumption that it can't form element/element-like particles)

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sight19 t1_jdx0z40 wrote

For structure to form, you need to compress gas in a small volume. As gas is compressed, it's temperature increases and so do the random motions of the theoreticized WIMPs. That means that at a certain point, the gas cloud stops collapsing (this is also called 'virialization'). The only way to collapse further is if the gas cloud would leak out temperature somehow, and that can only happen via radiation. And dark matter can't radiate, so it can't cool further

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ThrowawayPhysicist1 t1_jdx8ewv wrote

This is a good explanation but there’s also just the simpler fact that if things can’t collide (and dark matter is mostly collisionless as famously seen in the bullet cluster) it’s hard to get it to “stick together”. So while gravitational force will get it form “dense halos” it’s fairly unlikely you’ll get something like planets or stars.

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