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Scientists discover our galaxy has previously unknown neighbours

The Magellanic Clouds and the Auxiliary Telescopes at the Paranal Observatory in the Atacama Desert in Chile. Only 6 of the 9 newly discovered satellites are present in this image. The other three are just outside the field of view. V. Belokurov, S. Koposov (IoA, Cambridge). Photo: Y. Beletsky (Carnegie Observatories)

TORONTO — Turns out the Milky Way has a few new neighbours.

Well, they’re not really new so much as they were unknown to us. Two groups of scientists have discovered a collection of dwarf galaxies orbiting our own galaxy, the closest of which lies about 100,000 light-years away. Of the nine objects discovered, it’s believed that three of them are definite dwarf galaxies, while the rest may be either dwarf galaxies or globular clusters, large collections of stars.

The findings were made by the Dark Energy Survey, headquartered at the U.S. Department of Energy’s Fermi National Accelerator Laboratory and scientists from the University of Cambridge.

“The discovery of so many satellites in such a small area of the sky was completely unexpected,” said Cambridge’s Institute of Astronomy’s Sergey Koposov, the Cambridge study’s lead author. “I could not believe my eyes.”

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The first image is a snapshot of DES J0335.6-5403, a celestial object found with the Dark Energy Camera. It is the most likely of the newly discovered candidates to be a galaxy, according to DES scientists. This object sits roughly 100,000 light-years from Earth, and contains very few stars – only about 300 could be detected with DES data. Fermilab/Dark Energy Survey
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The second image shows the detectable stars that likely belong to this object, with all other visible matter blacked out. Dwarf satellite galaxies are so faint that it takes an extremely sensitive instrument like the Dark Energy Camera to find them. Fermilab/Dark Energy Survey

Dwarf galaxies are the smallest known galaxies, comprised of just thousands of stars as opposed to galaxies such as our own which contain billions.

The small galaxies could help scientists better understand dark matter and dark energy, both of which are unseen, but make up 95 per cent of our known universe.

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You might ask yourself how it’s possible to not be aware of neighbours, especially ones that are entire galaxies. That’s because these small galaxies are about a billion times dimmer than our own galaxy and a billion times smaller.

This illustration maps out the previously discovered dwarf satellite galaxies (in blue) and the newly discovered candidates (in red) as they sit outside the Milky Way. Yao-Yuan Mao, Ralf Kaehler, Risa Wechsler (KIPAC/SLAC)

The Dark Energy Survey, a research program that is trying to discover why our universe is expanding and the role dark energy plays.

These new dwarf galaxies are not the first of their kind to be discovered around the Milky Way. More than 24 had been found previously. However, it has been almost a decade since the last discovery.

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