Inside Rensselaer
* Mapping the History of Our Galaxy
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Stars from the Sagittarius dwarf galaxy are being spread all around the Milky Way, contributing to the lumpiness of the distribution of stars found in SDSS. In this illustration, the Milky Way is shown in yellow and the sun is a green star. The white dots show the expected positions of the stars from a simulation done by Rensselaer graduate student Ben Willett. The blue dots show the positions of actual stars extracted from the SDSS database by graduate student Nate Cole. The red dashed line shows the general direction all of the stars are going as they orbit around the center of the Milky Way.

Mapping the History of Our Galaxy
Heidi Newberg (fourth from left) co-organized a collaborators meeting in China. The picture above is taken in front of the LAMOST telescope.
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Mapping the History of Our Galaxy
Rensselaer’s Heidi Jo Newberg has spent the past eight years immersed in the Milky Way, sifting through images of a hundred million stars, tracking the motions of 240,000 of them, and helping to map the history of the galaxy. Her discoveries have enhanced our understanding of the Milky Way, raised additional questions about dark matter — and sent Newberg in search of an even larger spectroscopic survey.

An associate professor of physics, applied physics, and astronomy, Newberg initiated the Sloan Extension for Galactic Understanding and Exploration (SEGUE), one of three projects included in the Sloan Digital Sky Survey II (SDSS-II). She also was chair of the Stars Working Group for SDSS-I.

SDSS is one of the most ambitious astronomical surveys ever undertaken. Over eight years (SDSS-I: 2000-2005, SDSS-II: 2005-2008), SDSS measured the brightness and positions of hundreds of millions of galaxies, stars, and quasars. Data was released to scientists annually, with the final release on Oct. 31, 2008.

SDSS-III is now under way and its SEGUE-II will build on the research conducted by Newberg and her collaborators from 18 institutions worldwide. Newberg also is hoping to probe even deeper by partnering with the scientists who will survey the stars of the Milky Way using China’s Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), which is nearing completion.

“Most of the mass in the Milky Way is dark matter,” Newberg explained. “The only way we can probe that is to look more closely at the stars. If we can determine their velocity, we can see which direction they’re moving in, and can understand how dark matter is distributed in our galaxy.”

Since SDSS gathered so much data, a great deal has yet to be analyzed. Eventually, data from SDSS and subsequent surveys will produce the first three-dimensional map of the Milky Way and the motions of the stars.

Some of the data also has pointed researchers, including Newberg, in new directions. When SDSS began, scientists thought that the stars in the outer parts of the Milky Way formed one component of the galaxy with a smoothly varying density.

Instead, Newberg and her colleagues found that there were enormous lumps of stars, as far across as the distance between the sun and the center of the Milky Way, and some which stretched 360 degrees around the sky. The lumpy outer parts of the galaxy are proof that some, or maybe all, of the Milky Way was formed from the merging of smaller “dwarf” galaxies together to make one large, spiral galaxy.

Newberg designed the SEGUE survey to measure the velocities of stars in these large, lumpy streams of stars in the Milky Way, taking data samples about every 15 degrees. “On every scale that we looked at, we saw structure in the velocities,” Newberg said. “It became increasingly clear that to learn how the Milky Way formed, we really need a much bigger spectroscopic survey.”

Newberg began searching for a telescope capable of such a survey and found LAMOST at the Xinglong Observing Station, 170 kilometers northeast of Beijing. Inspired by SDSS’s 2.5-meter telescope in New Mexico, LAMOST has a 4-meter correcting mirror and a spectrograph that can take data for 4,000 stars at a time, which will make it the most powerful spectroscopic telescope in the world.

Among LAMOST’s goals is to extend SDSS’s discoveries, and Newberg hopes to play a role. At the very least, as a member of LAMOST’s galactic structure survey working group, she will help point the survey in the right direction.
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Inside Rensselaer, Strategic Communications and External Relations
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Inside Rensselaer
Volume 2, Number 19, November 14, 2008
©2008 Rensselaer Polytechnic Institute
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