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.。

The answer has to do with a cosmic near collision that occurred billions of years ago.。

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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.。

This animation cycles between a view of high-energy x-rays in the center of the Perseus cluster (blue, green) and low energy x-rays (red) over a wider area.Credit: NASA/CXC/SAO/E.Bulbul, et al.。

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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Part of the reason why scientists think the gas bubble formed from a galactic close encounter is because the other suspect for manipulating gravity on such a large scale is a super massive black hole, and computer model simulations don't support that scenario.。

An annotated view of the wave in the galaxy cluster.Credit: NASA's Goddard Space Flight Center/Stephen Walker et al.。

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.
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"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." 。

If all of this is a little difficult for you to visualize, just think of the wave as something like a giant Kelvin-Helmholtz cloud formation on Earth, which look like cartoon-versions of ocean waves in the sky.。

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