Sorry tytower that is absolutely incorrect, material is always falling towards a black hole, the gravity is always there, there is however not always matter nearby for it to consume, black holes are not only at the Galactic center or in solar systems, they can exist pretty much anywhere, including traveling through interstellar medium, which contains so little material there's no way to detect them other than gravitational lensing and you have to know exactly where one is to observe even that; these are 'true' black holes as we can't detect them outside of theoretically, no practical method has been used to discover inactive black holes that I'm aware of.
Active black holes are easy to spot, they suck up matter and spew out energy in a myriad number of ways.