# Black hole formation and Planck Density

**URL:** <https://boards.straightdope.com/t/black-hole-formation-and-planck-density/509174>\
**Category:** Factual Questions\
**Created:** [September 7, 2009, 5:26pm UTC](https://boards.straightdope.com/t/black-hole-formation-and-planck-density/509174 "2009-09-07T17:26:24Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Enola\_Straight](https://avatars.discourse-cdn.com/v4/letter/e/dec6dc/32.png) [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)\
**Post date:** [September 7, 2009, 5:26pm UTC](https://boards.straightdope.com/t/black-hole-formation-and-planck-density/509174/1 "2009-09-07T17:26:24Z")

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A star collapses in stages depending on it’s initial mass:

A Stellar Mass on par with our Sun will collapse to a white dwarf.  
A little bigger star will collapse to a neutron star: just a smidgen bigger, and you collapse to a quark star.

At about 3 solar masses, you infinitely collapse to a quantum singularity…a Black Hole.

in Planck units, what magical density does infinite collapse take place, and how does that relate to the Planck density?

> **[Planck units](https://en.wikipedia.org/wiki/Planck_density)**
>
> In particle physics and physical cosmology, Planck units are a set of units of measurement defined exclusively in terms of four universal physical constants, in such a manner that these physical constants take on the numerical value of 1 when expressed in terms of these units. Originally proposed in 1899 by German physicist Max Planck, these units are a system of natural units because their definition is based on properties of nature, more specifically the properties of free space, rather than...

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**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\
**Post date:** [September 7, 2009, 5:55pm UTC](https://boards.straightdope.com/t/black-hole-formation-and-planck-density/509174/2 "2009-09-07T17:55:09Z")

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I don’t believe the answer to your question is exactly known for the evolution of a stellar black hole, mainly because the value of the [Tolman-Oppenheimer-Volkoff limit](http://en.wikipedia.org/wiki/Tolman-Oppenheimer-Volkoff_limit), which gives the maximum mass for neutron stars, isn’t known exactly.

Generally, though, if you compress any amount of mass into a volume smaller than (or equal to) a sphere whose radius is just the Schwarzschild radius for that mass, you will get a black hole as a result, corresponding to a density way, way lower than the Planck density.