I may be invisible, but I matter a lot! My gravity is so strong because a lot of matter has been squeezed into a very tiny space. One atom may weigh as much as a mountain! As no light can get out, I can't be seen in the ordinary sense. Scientists have to use clever methods to detect my presence by observing my effects on the stars and gases around me. As surrounding dust and gasses get sucked inside me, they are heated to very high temperatures, releasing x rays and gamma rays which scientists can "see" with special telescopes. There is still a lot of research to be done. Until then, nobody really understands me!
The Black Hole Celestial Buddy is an 18"x16.5" stuff sack designed to hold all of the Celestial Buddies. The Black Hole is recommended for ages 6 and up.