Galaxies- a system of millions or billions of stars, together with gas and dust, held together by gravitational attraction. They come in many sizes and shapes with either spiral or elliptical shapes. Galaxies include things such as: stars and solar systems, dust, gas, dark matter, antimatter, and black holes. Black holes are a region of space having a gravitational field so intense that no matter or radiation can escape. Not even the fastest thing known to man--light-- can escape it. Black holes are unable to be seen by humans because the capture all the light around it. They form when a major star collapses. Scientists have found proof that every large galaxy contains a supermassive black hole at its center