Editing Compact object (section)

==Black holes==
{{Main|Black hole|Stellar black hole}}
[[Image:Black Hole Milkyway.jpg|upright|thumb|A simulated black hole of ten solar masses, at a distance of 600&nbsp;km]]
As more mass is accumulated, equilibrium against gravitational collapse exceeds its breaking point. Once the star's pressure is insufficient to counterbalance gravity, a catastrophic gravitational collapse occurs within milliseconds. The [[escape velocity]] at the surface, already at least {{frac|1|3}}&nbsp;light speed, quickly reaches the velocity of light. At that point no energy or matter can escape and a [[black hole]] has formed. Because all light and matter is trapped within an [[event horizon]], a black hole appears truly [[black]], except for the possibility of very faint [[Hawking radiation]]. It is presumed that the collapse will continue inside the event horizon.

In the classical theory of [[general relativity]], a [[gravitational singularity]] occupying no more than a [[point (geometry)|point]] will form. There may be a new halt of the catastrophic gravitational collapse at a size comparable to the [[Planck length]], but at these lengths there is no known theory of gravity to predict what will happen. Adding any extra mass to the black hole will cause the radius of the event horizon to increase linearly with the mass of the central singularity. This will induce certain changes in the properties of the black hole, such as reducing the tidal stress near the event horizon, and reducing the gravitational field strength at the horizon. However, there will not be any further qualitative changes in the structure associated with any mass increase.

===Alternative black hole models===
* [[Fuzzball (string theory)|Fuzzball]]<ref name="small-dark-and-heavy">{{cite arXiv |last1=Visser |first1=M. |last2=Barcelo |first2=C. |last3=Liberati |first3=S. |last4=Sonego |first4=S. |date=2009 |title=Small, dark, and heavy: But is it a black hole?  |class=gr-qc |eprint=0902.0346}}</ref>
* [[Gravastar]]<ref name="small-dark-and-heavy"/>
* [[Dark-energy star]]
* [[Black star (semiclassical gravity)|Black star]]
* [[Magnetospheric eternally collapsing object]]
* [[Dark star (Newtonian mechanics)|Dark star]]<ref name="small-dark-and-heavy"/>
* [[Primordial black hole]]s