is this good intro"A black hole is an astronomical object with a gravitational pull so strong that nothing, not even light can escape it. The concept of black hole was foreseen as precise mathematical answer to Einstein's formulas. These equations from Einstein illustrate the configuration of space surrounding physical matter. Globular cluster, dense combination of stars, are known to harbor stellar -mass black holes, remnants of massive stars' end of life cycles or the result of stellar remnant merging