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Messier 94 forces scientists to rethink galaxy formation models

"Our results indicate that Milky Way-like galaxies most likely host a much wider diversity of satellite populations than is predicted by any current model," researcher Adam Smercina said.

By Brooks Hays
Messier 94 forces scientists to rethink galaxy formation models
A pair of images captured by the Hyper Suprime-Cam on the Subaru telescope showcase the two satellite galaxies found circling the Milky Way-like galaxy M94. Photo by Smercina et al. 2018

Jan. 10 (UPI) -- Scientists have discovered a Milky Way-like galaxy with surprisingly few satellite galaxies. The findings may force cosmologists to revise current galaxy formation models.

Scientists knew the galaxy Messier 94, or M94, was similar in size and shape to the Milky Way. As such, researchers hoped a closer look would offer clues as to how satellite galaxies coalesce to form large spiral galaxies.

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Astronomers believe the Milky Way is the product of a succession of galaxy mergers. As it grew in size, its gravitational pull lured in smaller satellite galaxies. Today, the Milky Way is surrounded by 10 satellite galaxies. Astronomers expected to find a similar number of galactic satellites around M94.

Instead, they found just two -- each with a surprisingly small stellar population.

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"More than just an observational oddity, we show that the current crop of galaxy formation models cannot produce such a satellite system," Adam Smercina, an astronomer and research fellow at the University of Michigan, said in a news release. "Our results indicate that Milky Way-like galaxies most likely host a much wider diversity of satellite populations than is predicted by any current model."

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Scientists think galaxies like the Milky Way form in large halos of dark matter. The gravitational pull of these giant rings of dark matter help pull smaller galaxies into orbit around the central galaxy.

Smaller satellite galaxies also form within dark matter halos, but the latest findings suggest these smaller halos are less stable than scientists thought.

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"The real kicker is whether or not the community expected this could be possible," Smercina said. "That is the real curiosity of this finding -- the result is something the simulations don't predict. When you can discover something we didn't really think we could find, you can make a contribution to our understanding of how our universe works, that's really rewarding."

Smercina and his colleagues detailed their analysis of Messier 94 in the Astrophysical Journal Letters.

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