The rings are actually multiple layers of interstellar dust between 4,000 and 7,000 light years away. Some X-rays from the black hole burst hit Swift's X-ray detectors directly, while others reflected off the dust, delaying their arrival slightly. That makes the rings appear to "echo" into space, the same way that sound reverberates in a canyon. The echoing is useful to scientists, helping them see the rings evolve over time. "With these observations, we can make a detailed study of the normally invisible interstellar dust in the direction of this black hole," said lead researcher Andrew Beardmore.
The researchers aren't totally sure why V404 Cygni's X-ray bursts happen so sporadically, but they do have a theory. The black hole's companion star orbits it every 6.5 days at a close distance, meaning it's likely distorted into an egg shape by the gravity. Material ejected by the star accumulates around the black hole until it reaches critical mass. At that point, "thermonuclear runaway" fusion rapidly burns up the material, creating a bright X-ray flash. Suffice it to say, that's just one reason you wouldn't want to live on a planet in that star's system, as Interstellar showed,