For 10 points, name these astronomical objects named for the fact that they don't let light escape.
Gullstrand–Painlevé coordinates can be used to express the velocity of an object approaching one of these systems as the negative of Newtonian escape velocity. Other coordinate systems used for studying these systems include Eddington–Finkelstein coordinates and Kruskal coordinates, which present maximally extended solutions and represent radial light-like geodesics as 45-degree lines. The Kerr metric describes rotating, uncharged examples of these objects. In September 2015, LIGO detected gravitational waves generated by the merger of two of these objects. Their extent is defined by their Schwarzschild radius and they have a singularity at their center. For 10 points, name these astronomical objects named for the fact that they don't let light escape.
Gullstrand–Painlevé coordinates can be used to express the velocity of an object approaching one of these systems as the negative of Newtonian escape velocity.
black holes &lt;Overman&gt;