Now you see it, now you don't. In 2002, observations from the Chandra X-ray observatory showed about what you'd expect for a nearby galaxy with an active supermassive black hole at its center: intense emissions in the UV and X-ray regions of the spectrum. By 2003, however, follow-up observations showed that emissions of energetic photons had dropped off precipitously. This odd disappearance led scientists to organize a massive campaign of follow-up observations, the results of which were released by Science today.
The new observations suggest that a large cloud of gas has walled off the black hole from Earth's line of sight to the galaxy. But the cloud is moving so fast and has persisted so long that it must be drawing material away from the environment around the black hole.
The galaxy in question, NGC 5548, belongs to a class of objects called Seyfert galaxies. These have active black holes that are feeding on gas, creating a highly energetic accretion disk. These galaxies don't emit as much radiation as a quasar (the brightest objects in the Universe), but they have the advantage of being found much closer to Earth than quasars, making them more amenable to study.
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