New observations from the Kitt Peak National Observatory suggest there is a second cloud of gas at the scene.
"The idea of the Pleiades and one gas cloud in an interstellar train wreck already made this nearby cluster an especially interesting region for astronomers seeking to understand the details of physical and chemical processes in the interstellar medium," said study leader Richard White of Smith College in Northampton, MA. "The presence of a second cloud interacting with the first cloud and with the cluster creates a situation more like a three-car crash in a demolition derby, which makes the Pleiades altogether unique as natural laboratory."
White collaborated with students from Smith College and Amherst College. The researchers examined light from the nebulous region around the stars, splitting it into its many colors and discerning the direction and speed of the gas.
Interstellar gas clouds can be the seeds of star formation, if they are dense enough for gravity to create an eventual collapse. Nebulas do not necessarily involve interstellar clouds. The gas in many celebrated nebulas comes from the stars embedded in them.
Astronomers figured out in the 1980s that the Pleiades cluster was moving through a cloud of gas otherwise not associated with the cluster's stars. White and his colleagues say this sort of apparent interaction of a star cluster with two separate clouds has never been seen before.
Also called M45, Pleiades holds more than 500 very young stars, all roughly 100 million years old and centered about 400 light-years from Earth. Our Sun is about 4.6 billion years old. The cluster is known to many skywatchers as the Seven Sisters for the seven stars visible with the naked eye under dark-sky conditions.
The finding is published in the October Astrophysical Journal Supplement. Photos of the cluster do not reveal the individual clouds.
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