Figure: Curvature of space-time

An effect of a mass!

Einstein's general relativity describes gravity as a curvature of the space-time continuum. The more concentrated the mass, the more curvature you obtain.

If we draw the framework of space-time as a two-dimensional plane (there are actually 4 dimensions: 3 for space and one for time), we can visualize this curvature in the 2D case, as an "elastic distortion" (see picture).

In the case of a black hole, the curvature may have no end: there would be a tear in the fabric of space-time, an "infinitely deep" hole, from which nothing can escape, not even light...

Credit: http://nrumiano.free.fr/Estars/b_holes.html