The name given to a location in space where gravity is so powerful that it prevents even light
from escaping. Black holes are most commonly created when particularly massive stars reach the
ends of their life-cycles. If the core of such a star collapses beyond a point known as the
Schwarzchild radius (a matter of a just few kilometres across, in most cases), its gravity
will become so intense that it will form a black hole. Though black holes are invisible by definition, they can be observed
indirectly through their effects on surrounding matter. For example, matter falling into a black hole is detectable by the
X-ray energy it emits.