How many black holes are in the observable universe? How fast do they spin?
These are just a few of the questions the @NASAJPL NuStar space telescope is set to answer soon. The NuStar space telescope is an x-ray telescope, which gives it the ability, just like medical telescopes, to peer beyond the things we cannot see with conventional light. And in addition to the free-floating black holes that exist, science now knows that the heart of every galaxy including the Milky Way is a black hole. So, getting past all the star-dust, suns and planets is key to understanding these ubiquitous mysteries of the universe.
For example, understanding how fast black holes spin is a key task for NuStar. As matter orbits any object in space, it generally falls in a circular pattern around the object. This is called an orbit. And orbits generally are not static: they either decay, eventually leaving the satellite to fall into its gravitational focus, or else the satellite may have too much mass or speed, in which case, it may fly free of its gravitational focus.
But with black holes, things work a little differently. As matter gets closer to a black hole, the black hole warps space and time, accelerating the matter. This in turn allows much more matter to orbit the black hole without actually falling in. If that sounds counterintuitive for black holes, which we think of as space dustbusters, it is. Yet more mystery.