Luck for the average pedestrian is happening upon a crisp dollar bill tumbling down the sidewalk. For European astronomers, it's happening to be looking at the right portion of sky at the exact moment a star is ripped apart by a giant black hole.

The auspicious discovery was made by the European Space Agency's orbiting X-ray observatory XMM-Newton. The cosmological providence revealed not one black hole, but two -- the first pair of supermassive black holes observed in a normal galaxy. Normal galaxies, or quiescent galaxies -- as opposed to active galaxies -- are no longer actively producing stars.

Black holes are much easier to locate in newer active galaxies. Finding them in normal galaxies -- as mentioned -- requires luck. While black holes in active galaxies are constantly eating up gas clouds and star matter, giving off detectable X-rays as a result, similar activity is less frequent and more sporadic in normal galaxies.

Currently, the only way to find a normal black hole is by happening upon a "tidal disruption event," like the star consumption witnessed by ESA's XXM-Newton.

What makes the latest discovery even more unusual is that the two black holes were found together, orbiting each other -- the product of two galaxies having merged.

Scientists hope this just the first of many similar discoveries to come.

"There might be a whole population of quiescent galaxies that host binary black holes in their centers," explained astronomer Stefanie Komossa, of the Max Planck Society in Germany.

With further analysis of binary black holes, scientists hope to learn how and at what rate galaxies merge with each other. "Once we have detected thousands of tidal disruption events, we can begin to extract reliable statistics about the rate at which galaxies merge," Komossa said.

Eventually, these two newly discovered black holes will merge, and the result will be a massive burst of energy. The final merger will be the strongest source of gravitational waves the universe has ever seen.

Details of the new binary supermassive black holes will be published next month in The Astrophysical Journal.