The team leaders for this Hubble Space Telescope project are Assistant Professor Nitya Kallivayalil from the University of Virginia in Charlottesville, and Professor Roeland van der Marel of the Space Telescope Science Institute and Johns Hopkins University, in Baltimore.
Within a seven-year period, the Hubble telescope was used to measure very slight movements in hundreds of individual stars in a galaxy called the Large Magellanic Cloud, adjacent to our closest galaxy, known as the Milky Way, which is roughly 170,000 light-years' distant from us.
For some time, in exploring near-field cosmology, astronomers have been able to measure the sideways directional motions of celestial objects that are closeby; but now the precision tracking of the Hubble Telescope has enabled virtually a three-D perspective, allowing the motion of the field itself to be captured in the process of rotation, and recorded.
Professor Kallivayalil explains:
"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."
Professor van der Marel, who is the lead author on the paper now published in the Feb. 1 issue of the Astrophysical Journal, notes:
"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."
For at least one hundred years now, it has been possible to calculate galaxy rotation rates by what's known as the Doppler Effect; by observing a slight shift in the spectrum of the galaxy's starlight, indicating that on one side of its spinning disk of stars, those stars that swing toward the Earth show a blue-shift in the compression of the light waves, and those stars that swing away from the Earth on the opposite side of the galaxy, will show a redshift on a light spectrum -- due to the motion of those stars away from the observer.
These Doppler motions that had been previously measured, coupled with those now measured by the Hubble telescope, have provided for the first time a combination of results that has allowed the team to gain what they have described as “a fully three-dimensional view of stellar motions in another galaxy.”
Because of its very sharp resolution, and its capacity for image stability -- as well as its having been operative for nearly a quarter-century -- only the Hubble telescope can make this unique form of observation.
Professor van der Marel explains further:
"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. 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."
Professor van der Marel's experience at the Space Telescope Science Institute and at earlier at the Massachusetts Institute of Technology, allowed him to develop expertise with two of the instruments on the Hubble Space Telescope: in calibration for the Advanced Camera for Surveys (ACS) and in the Wide Field Planetary Camera 2 (WFPC2). He now assumes leadership for the team that is responsible for “issues related to the telescope structure, guiding, focus, and Wavefront Sensing and Control" on both the Hubble Space Telescope, and for the future James Webb Space Telescope , which is to be launched in 2018:
"The James Webb Space Telescope (sometimes called JWST) will be a large infrared telescope with a 6.5-meter primary mirror. The project is working to a 2018 launch date.
The Webb will be the premier observatory of the next decade, serving thousands of astronomers worldwide. It will study every phase in the history of our Universe, ranging from the first luminous glows after the Big Bang, to the formation of solar systems capable of supporting life on planets like Earth, to the evolution of our own Solar System."
This next inquiry for this particular team, however, will involve the use of the Hubble in measuring the stellar motions in the Small Magellanic Cloud, using the same technique as had been practiced here. Since the two galaxies are interacting and moving around one another -- and are also moving around the Milky Way -- the team expects that even greater insight is to be developed through this next step.
A graphic and video illustration of these results is available by visiting here.
Additional information about NASA's Hubble Space Telescope is available by visiting here.