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NASA scientists may have just solved the galactic mystery of how a huge wave of gas formed in a cluster of galaxies more than 200,000 light-years away. 
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The answer has to do with a cosmic near collision that occurred billions of years ago.。

Scientists working with NASA's Chandra X-Ray Observatory and other teams now think that the wave of gas seen in the Perseus galaxy cluster was created when a smaller cluster of galaxies "grazed" the Perseus cluster sometime in its past, causing some of its gas to "slosh" around, NASA said in a statement.。

"The wave we've identified is associated with the flyby of a smaller cluster, which shows that the merger activity that produced these giant structures is still ongoing," NASA's Stephen Walker said.。

The findings are detailed in a new study published in the journal 。 The findings are detailed in a new study published in the journal。

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An annotated view of the wave in the galaxy cluster.Credit: NASA's Goddard Space Flight Center/Stephen Walker et al.
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The researchers put together the simulations to try to explain how the wave of gas formed. One of those simulations showed a galaxy cluster brushing by the Perseus cluster and displacing some of its gas.。

"The flyby creates a gravitational disturbance that churns up the gas like cream stirred into coffee, creating an expanding spiral of cold gas," NASA said in the statement. 。

"After about 2.5 billion years, when the gas has risen nearly 500,000 light-years from the center, vast waves form and roll at its periphery for hundreds of millions of years before dissipating."。

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