If the only things you can believe in are the things you can see then you can't believe in Black Holes. Then again, you can't believe in many things like sound, love and light (you don't actually see light you see the reflection of the spectrum of light).

If you understand physics related to light, mass and gravity then you can understand a Black Hole and how they can exist.

A Black Hole forms when a star with a certain mass and above collapses in on itself thru gravity. Supernova, super-massive supernovas and stellar collisions cause Black Holes. Planets are not massive enough to create a Black Hole.

A Black Hole is gravity that has gone to the extreme. To the point that not even the particles in photons can escape its influence. If light can't escape it cannot reflect, thus Black. Light goes in but cannot come back out because gravity keeps it there.

Black Holes are not sheets being drawn into a hole to a destination. Black holes are matter that has so much mass it compresses to a point in space. Black holes have at their centers what is called a singularity. A particle of matter so dense its gravity continuously draws in nearby masses, all nearby masses, including light.

Think of it as a ping pong ball hovering in space in front of you. It is a sphere of influence not a funnel. Gravity is like arrows pointing in on the ball from all directions at once. As the gravity/mass increases the ball gets smaller and smaller until you can no longer see it. You only know it is there because it is trying to pull you down onto its mass.

We detect Black Holes by looking at their influence over the matter near them. Energy does emit from Black Holes. High frequency energy waves have been detected in the High Gamma range.

Reality doesn't care if you believe in it or not, it just is...