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Record-breaking faint satellite galaxy orbiting Milky Way

"This discovery implies hundreds of faint dwarf satellites waiting to be discovered in the halo of the Milky Way," said lead researcher Masashi Chiba.

By Brooks Hays

SENDAI, Japan, Nov. 22 (UPI) -- Astronomers have discovered an extremely faint dwarf galaxy orbiting the Milky Way. It is the faintest satellite galaxy yet found within the Milky Way's sphere of gravitational influence.

Scientists named the new galaxy Virgo I. Astronomers have identified 50 satellite galaxies related the the Milky Way, but Virgo I suggests there are more hiding in the halo of the Milky Way.


Like most Milky Way satellites, Virgo I is a dwarf spheroidal galaxy.

Astronomers were able to pick up Virgo's low magnitude wavelengths using Japan's Subaru Telescope and its large field-of-view Hyper Suprime-Cam instrument.

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Scientists look for faint galaxies by scanning stellar surveys for "over density" of stars in the sky. Researchers then use a color-magnitude diagram to study the stars' distribution and confirm their organizational logic.

"We have carefully examined the early data of the Subaru Strategic Survey with HSC and found an apparent over density of stars in Virgo with very high statistical significance, showing a characteristic pattern of an ancient stellar system in the color-magnitude diagram," Daisuke Homma, a graduate student at Tohoku University, said in a news release.

Part of understanding how the Milky Way formed involves modeling the assemblage and organization of dark matter. Scientists believe the logic of galaxy formation is explained by the hierarchical assembly of dark matter -- a dark matter superstructure made up of small dark matter halos.

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Models simulating the formation of the Milky Way predict a large ring of dark halos -- a halo of halos -- orbiting the Milky Way. Simulations also predict the presence of several corresponding luminous galaxies.

So far, the number of faint satellite galaxies discovery by astronomers falls short of model predictions. It's known as the "missing satellite problem."

The discovery of Virgo I -- which scientists detailed in the Astrophysical Journal -- suggests astronomers may not be far from solving the problem.

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"This discovery implies hundreds of faint dwarf satellites waiting to be discovered in the halo of the Milky Way," said lead researcher Masashi Chiba, also of Tohoku University. "How many satellites are indeed there and what properties they have, will give us an important clue of understanding how the Milky Way formed and how dark matter contributed to it."

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