For the first time, astronmers are set to witness a black hole consuming a gas cloud. Black hole Sagittarius A* is expected to pull the cloud past its event horizon at some point in 2013, with the whole process likely taking a decade before the cloud has been completely absorbed.
Black holes are known to consume matter around them. Their pull is so great that beyond the event horizon nothing can escape, not even light. Some parts of the gas cloud are likely to avoid being sucked in as the integrity of the whole breaks down and the furthest parts drift away before passing the event horizon, but most of the cloud will go straight into the black hole.
The chance to witness Sagittarius A* consuming the gas cloud will be the first real chance to watch such a process, although it is unlikely to help answer some of the more persistent questions about exactly how these extremely dense phenomena occur in the first place.