According to Gomez, his team’s detection of an interstellar cloud near the gas jet in galaxy 3C120 was a complete surprise. "The finding was a serendipity discovery, since we weren’t actually looking for this cloud," said Gomez.

Artist's conception of an active galaxy, complete with a streaming plasma jet emanating from the center. A jet like this that was found to have collided with a local cloud of gas and dust.

Initially, the astronomers working with the VLBA were aiming simply to study the physics of jets coming from active galaxies. They had been tracking the motion of "blobs" in the jet, concentrations of matter streaming out from the center of C3120 that had already reached a distance of about 25 light-years from the galaxy’s central black hole.

The wandering gas cloud near C3120’s jet appears to be a condensation of matter belonging to the host galaxy, said Gomez, although astronomers still don’t know exactly how the cloud is behaving. "We’re not sure whether these clouds are moving away from the black hole, toward it or in some random manner," he said. The cloud may also be "similar to those from which stars and planets are born," added Gomez.

Future studies with the VLBA, a subset of the National Radio Astronomy Observatory, will allow astronomers to look at more jet-cloud interactions, including the one near C3120. In particular, astronomers hope to find out how big the cloud near C3120 is, how dense it is, and how it’s moving relative to the galaxy’s central black hole. "Ultimately this will help to understand better the central regions of active galaxies, and in particular the neighborhood of the central black hole," said Gomez.