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Milky Way kidnapped several tiny galaxies from its neighbor

Christian Fernsby ▼ | October 15, 2019
Just like the moon orbits the Earth, and the Earth orbits the sun, galaxies orbit each other according to the predictions of cosmology.
Milky Way
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For example, more than 50 discovered satellite galaxies orbit our own galaxy, the Milky Way.

The largest of these is the Large Magellanic Cloud, or LMC, a large dwarf galaxy that resembles a faint cloud in the Southern Hemisphere night sky.

A team of astronomers led by scientists at the University of California, Riverside, has discovered that several of the small or "dwarf" galaxies orbiting the Milky Way were likely stolen from the LMC, including several ultrafaint dwarfs, but also relatively bright and well-known satellite galaxies, such as Carina and Fornax.

The researchers made the discovery by using new data gathered by the Gaia space telescope on the motions of several nearby galaxies and contrasting this with state-of-the-art cosmological hydrodynamical simulations.

The UC Riverside team used the positions in the sky and the predicted velocities of material, such as dark matter, accompanying the LMC, finding that at least four ultrafaint dwarfs and two classical dwarfs, Carina and Fornax, used to be satellites of the LMC.

Through the ongoing merger process, however, the more massive Milky Way used its powerful gravitational field to tear apart the LMC and steal these satellites, the researchers report.

"These results are an important confirmation of our cosmological models, which predict that small dwarf galaxies in the universe should also be surrounded by a population of smaller fainter galaxy companions," said Laura Sales, an assistant professor of physics and astronomy, who led the research team.

"This is the first time that we are able to map the hierarchy of structure formation to such faint and ultrafaint dwarfs."

The findings have important implications for the total mass of the LMC and also on the formation of the Milky Way.