Large Magellanic Cloud Completes One Rotation Every 250M Years

Lee Rannals for redOrbit.com – Your Universe Online

Scientists using NASA’s Hubble Space Telescope found that the Large Magellanic Cloud (LMC) completes a rotation every 250 million years.

The team used Hubble to measure the average motion of hundreds of individual stars in the nearby galaxy, which is located about 170,000 light-years from Earth.

“Studying this nearby galaxy by tracking the stars’ movements gives us a better understanding of the internal structure of disk galaxies,” Nitya Kallivayalil of the University of Virginia in Charlottesville, Va., said in a statement, “Knowing a galaxy’s rotation rate offers insight into how a galaxy formed, and it can be used to calculate its mass.”

LMC generally rotates likes a carousel, and Hubble’s tracking was able to offer up a new way to determine a galaxy’s rotation by the “sideways” proper motion of its stars.

“The LMC is a very important galaxy because it is very near to our Milky Way,” Roeland van der Marel, who is the lead author on a paper published in the Astrophysical Journal, said in a statement. “Studying the Milky Way is difficult because you’re studying from the inside, so 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.”

Hubble’s motion measurements, along with Doppler Effect motion measurements previously provided, have helped provide the new details about LMC’s rotation rate. Astronomers combined these results to create a three-dimensional view of stellar motions in another galaxy.

“By using Hubble to study the stars’ motions over several years, we can actually, for the first time, see a galaxy rotate in the plane of the sky,” van der Marel said in a statement.

Each field observed by the team contains dozens of LMC stars as well as background quasars, which were used as fixed reference points to measure the subtle motions of the stars. This measurement is part of an ongoing project aimed at refining the calculation of LMC’s rotation rate.

“Because the LMC is nearby, it is a benchmark for studies of stellar evolution and populations,” Kallivayalil said. “For this, it’s important to understand the galaxy’s structure. 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.”

Next, the team hopes to measure the stellar motions of the Small Magellanic Cloud by using both the Hubble and the same techniques. NASA said the study should yield improved insight into how the galaxies are moving around each other and around the Milky Way.