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I have recently read a bit a out Bok globules. One thing, that is repeatedly emphasised is that they are among the coldest objects in space, with a temperature of ~3 K.

Why is that so? Naively, I would expect the coldest objects to be far out in the super voids. Also, I would expect these globules to have retained heat from the gravitational collapse. After all, the kinetic energy of their free fall should be dissipated, shouldn't it?

Maybe someone can elaborate.

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    $\begingroup$ Do you have a source for them being so cold? $\endgroup$ – Steve Linton May 19 at 15:32
  • $\begingroup$ Its pretty cool to know that they may be more numerous than stars. $\endgroup$ – com.prehensible May 21 at 19:53
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Most of my information is sourced from here: https://apod.nasa.gov/apod/ap990511.html

To summarize the source, Bok globules are extremely cold because of their composition -- they're generally just clouds of pre-stellar material which block out all light. This makes the interior of Bok globules "shielded" from interstellar radiation that would otherwise heat them up.

Also, you claim that the globules should have retained some heat from gravitational collapse. However, since the globules don't encounter much friction in space, and there aren't many major collisions that produce changes in kinetic energy, there isn't much energy to dissipate. After all, even Bok globules aren't dense objects by any stretch of the imagination.

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