NASA's Hubble Telescope Used to Calculate 250-Million-Year Revolution of Nearby Galaxy

Astronomers using the Hubble Space Telescope have used stars in the Large Magellanic Cloud - or the LMC, the nearest galaxy to our own - to chart the galaxy's rotation.

According to the results, the LMC completes a rotation every 250 million years, about the same time it takes for the Sun to complete a rotation around the center of our own Milky Way galaxy.

The astronomers used the Hubble telescope to measure stars 170,000 light years away in the LMC, charting their movements over seven years. The data were then extrapolated to calculate the time it takes for the LMC to make one revolution. The observations were made possible by the precision and stability of the Hubble telescope and because it has been in space for 24 years.

"If we imagine a human on the Moon, Hubble's precision would allow us to determine the speed at which the person's hair grows," said Roeland van der Marel of the Space Telescope Science Institute in Baltimore, Md.

"This precision is crucial, because the apparent stellar motions are so small because of the galaxy's distance," he said. "You can think of the LMC as a clock in the sky, on which the hands take 250 million years to make one revolution. We know the clock's hands move, but even with Hubble we need to stare at them for several years to see any movement."

Studying the rotation of the LMC not only revealed how long it takes to complete a rotation, but it helps astronomers get a better understanding of the nature of galaxies.

"Studying this nearby galaxy by tracking the stars' movements gives us a better understanding of the internal structure of disk galaxies. Knowing a galaxy's rotation rate offers insight into how a galaxy formed, and it can be used to calculate its mass," said Nitya Kallivayalil of the University of Virginia in Charlottesville, Va., who along with van der Marel published the details of their observations in the Astrophysical Journal.

"Because the LMC is so nearby, it is a benchmark for studies of stellar evolution and populations. For this, it's important to understand the galaxy's structure," Kallivayalil said. "Our technique for measuring the galaxy's rotation rate using fully three-dimensional motions is a new way to shed light on that structure. It opens a new window to our understanding of how stars in galaxies move."

Van der Marel added that observing the LMC is one of the best ways to study an galaxy in its entirety, as studying the Milky Way from our own vantage point within it is difficult.

"The LMC is a very important galaxy because it is very near to our Milky Way," he said. "Studying the Milky Way is very hard because everything you see is spread all over the sky. It's all at different distances, and you're sitting in the middle of it. Studying structure and rotation is much easier if you view a nearby galaxy from the outside."

In the future, the team plans to use the same techniques to measure the rotation of the LMC's less sizable cousin the Small Magellanic Cloud.