NASA's Hubble Measures the Motion of Stars in Nearby Galaxy

Astronomers using NASA's Hubble Space Telescope have successfully measured the average rotation rate of several individual stars in the central part of the neighboring galaxy, the Large Magellanic Cloud.

In a latest announcement the space agency declared that using the Hubble space telescope, astronomers for the first time have precisely measured the average motion of a galaxy based on the movement of its stars. Such observation was possible because of Hubble and its sharp resolution.

The analysis of the nearest normal sized galaxy to our Milky Way was led by Roeland van der Marel of the Space Telescope Science Institute in Baltimore, Md., and Nitya Kallivayalil of the University of Virginia in Charlottesville, Va.

"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," van der Marel said in a news statement. "This precision is crucial, because the apparent stellar motions are so small because of the galaxy's distance. 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."

According to the study result, the Large Magellanic Cloud (LMC), completes a rotation every 250 million years, which is almost similar to the time taken by our Sun to complete a rotation around the center of the Milky Way Galaxy.

Using NASA's space telescope the astronomers measured the motion of hundreds of single stars in the LMC that is currently located 170,000 light years away. The slight movement of the stars in the center of the neighbouring galaxy was recorded over seven years.

"Studying this nearby galaxy by tracking the stars' movements gives us a better understanding of the internal structure of disk galaxies," said Kallivayalil, "Knowing a galaxy's rotation rate offers insight into how a galaxy formed, and it can be used to calculate its mass."

Our Milky Way galaxy and the LMC , both disk-shaped galaxies, are known to rotate in a circular manner. Using Hubble's precision tracking, the astronomers for the first time have observed the rotation rate of a distant galaxy.

"The LMC is a very important galaxy because it is very near to our Milky Way," said van der Marel. "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."

In the past, the rotation rate of the galaxy was calculated by monitoring the slight shift in the starlight, called the Doppler Effect.

The new measurements provided by Hubble and the Doppler motions together offer corresponding data on the rotation rate of LMC. Combining the two results the astronomers obtained a three dimensional view of the motion of the stars in a distant galaxy. This is the first time they were able to view the galaxy rotate in the plane of the sky.

To measure the motion of the LMC stars, the astronomers used quasars- light powered by a black hole in a distant galaxy, as a fixed reference points.

This finding offers improved insight into how galaxies move around each other and around the Milky Way. Next, the team plans to measure the stellar motion in the dwarf galaxy - Small Magellanic Cloud, LMC's diminutive cousin. They plan on implementing the same technique.

The finding was documented in the Astrophysical Journal.