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String of galaxies defy researchers’ expectations

by CIFAR Jan 31 / 13

Until now, scientists believed that the motions of satellite galaxies – small galaxies in orbit around a much larger one – were random and chaotic. But a recent discovery defies conventional thinking and suggests that a new model is needed to explain how galaxies form and behave.

Andromeda Galaxy.
Image credit : Jean-Charles Cuillandre (CFHT) and Giovanni Anselmi (Coelum Astronomia).

A team of astronomers, including Senior Fellow Julio Navarro (University of Victoria) of CIFAR’s Cosmology & Gravity program, observed the orbiting pattern of 13 small satellite galaxies around Andromeda – the nearest large galaxy to the Milky Way. To their surprise, the galaxies were moving synchronously and in a flat formation. This orbit formation has never before been observed, providing the team with evidence that our understanding of the origin of galaxies may need to be reconsidered. Their discovery was published in the prestigious journal Nature.

The standard model of galaxy formation suggests that galaxies form piece by piece, starting off as small bits and growing bigger and bigger over time, as they accumulate matter. The satellite galaxies should have developed in a similar way around Andromeda – moving in and becoming satellites of Andromeda one after another, from different directions and at different times. Because of their random addition, their movement around each other should have also been random.

“We didn’t expect any obvious relation between the satellite galaxies, yet what we saw was that they were rotating around Andromeda on a plane, behaving more like planets orbiting a star,” explains Navarro. “They should have been rotating around each other like bees in a bee hive. This tells us that there is some sort of underlying phenomenon that we have not considered before.”

The team made their discovery using observations from the Pan Andromeda Archaeological Survey, which uses the Canada-France-Hawaii Telescope to peer at the closest galaxies to our own Milky Way.

“The next steps for our team are to go deeper into the data, to try to find other satellite galaxies and see if the same findings still hold,” says Navarro. “We also need to look at our models and see under what conditions, if any, this order among galaxies may arise and what its origin is.”

This new observation of galaxy behavior will give scientists a deeper understanding of how galaxies form and behave, expanding the horizons of our understanding of the universe.