The problem with black holes is that the most interesting bits are hidden. The gravity of a black hole is such that everything—including light—is trapped if it gets closer than a certain distance. As a result, everything we observe about black holes comes from their effect on the world beyond that distance. Any closer and you pass the event horizon—the distance at which nothing escapes the black hole.

Jets are a common feature of black holes. They’re narrow streams of high-energy particles that stream away from outside the event horizon. Their energy is such that the jets glow brightly, revealing themselves to us.

These jets may be able to tell us something about the black holes themselves, but that requires two things. One is observations that require a globe-spanning telescope. The second, more difficult requirement is that we need models that help us understand the observations, as we haven’t built detailed models of the physics near the event horizon yet.