Porphyry, any igneous rock consisting of large crystals in a mass of much smaller crystals. The large and small crystals usually are of different minerals; the rock is generally named according to its major component (for example: granite porphyry). When cut and polished, porphyry has a beautiful pattern and contrast of colors. It is used for tombstones and ornamental panels.
A black hole occurs when a massive star dies -- its enormous mass implodes and becomes so heavy that it bends space. So how do astronomers detect something that they can't see?
While routinely scanning the stars, NASA scientists came across something they didn't expect to see: a vast area of space empty of stars, planets and matter.