THE BIG CRUNCH

Any size will do
                     Scientists believe a black hole can be any size.  But they don't know for sure.  They believe a black hole can be smaller than a pinpoint or have millions of times more material, or mass, thanour sun.
                     What they know for sure is that the massive black holes in space were probably all formed by dying stars.

It's really dense
                      A black hole is formed when a whole bunch of material (as from a star) is crammed into a tiny area (like a ball a few miles wide).
                      The more material that's smashed into a small volume, the more dense something is.  The more dense an object is, the stronger its gravity is.  A black hole is super dense.
                      If the Earth were smashed into the size of a marble, it would be dense enough to be a black hole.

They're everywhere
                      Scientists have discovered evidence that millions of stellar black holes are in every galaxy, including our own, the Milky Way.  (But don't worry, they can never pull us in.)
                      There is probably also a supermassive black hole in the Milky Way appears to weigh 2 million to 3 million times more than our sun.
                       Some experts believe that supermassive black holes may have helped form galaxies by pulling star material into their neighborhood.

When stars collide
                        Another idea scientists have is that when stars are coming together, supergigantic stars may collide and form supermassive black holes.  Or galaxies may collide, forming a supermassive black hole.