just decay like that over billions of years and inevitably just become cold matter like the rest of the universe? riyanatarajan: The timescale for decay by evaporation is too long....so they will simply be sitting around as the Universe becomes a colder and colder and lonelier place! ---: are you guys gonna do another one of these in the future on another subject? Jason: Yes. We try to do lots of chats from time to time. Keep checking http://www.nasa.gov/chat for the latest list of chats, both upcoming and previously held. We'll also post them to the NASA Facebook page and the @NASA twitter account. Thanks for your interest! blackholeuser: Has anyone ever seen a black hole how do you know if black holes really exsict ? Kevin: There are a number of ways. For example in the case of the black hole at the center of the Milky Way, we can work out the mass of whatever is there becuase we see stars orbiting a particular spot. And this object is so massive and compact that even if it was not a black hole, it would immediately collapse into one. Chateau: How large is the smallest black hole you've seen? riyanatarajan: The smallest black hole that we infer exists is something that likely weighs roughly as much as our Sun....10^33 grams. Kevin: The lightest black holes are black holes formed in supernovae and I think the lightest of them can be just a few times the mass of the sun.