Astronomers Successfully Measure the Motion of 66 Nearby Galaxies

by Ryan Whitwam

The heavens appear to move throughout the year, but that’s just because Earth is moving. The real or “proper motion” of stars and galaxies was beyond our ability to measure until fairly recently, but bigger, more powerful telescopes have helped paint a picture of an evolving universe. The European Space Agency’s Gaia space telescope has been particularly valuable in tracking the motion of stars inside our galaxy. But what about other galaxies? A team of astronomers has used Gaia to get insight into our celestial neighbors, determining the proper motion of a whopping 66 nearby galaxies.

This wasn’t as simple as just pointing Gaia at different galaxies and taking a picture. Gaia has revolutionized our understanding of stellar motion in the Milky Way because it has the ability to monitor the sky with high precision over long periods of time. The mission has a planned duration of five years, but the 34 months of data we have now has revealed proper motion for more than a billion stars. It took a long time to tease the necessary details out of the Gaia data for the more distant dwarf galaxies. For example, astronomers had to assess the color spectrum of stars to see if they matched the expected spectrum of the target galaxies.

The results are a watershed moment for our understanding of the Local Group. We’ve learned that six of these dwarf galaxies are actually gravitationally bound to the Large Magellanic Cloud, which itself has about…

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