Inside Rensselaer
* Heidi Newberg

Plotting the Spectrum of Stars

Heidi Newberg, associate professor of physics, has won a $1.3 million grant from the National Science Foundation to further her research into the structure of the Milky Way. The grant will create a partnership between Rensselaer and the cutting-edge Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) in China, allowing Newberg and a team of U.S. scientists to plot the position, speed, and composition — or “spectrum” — of more than 7 million stars.

If, for example, you wanted to take a spectrum of the sun, said Newberg, “you hold up a prism to the light, and if you have a really good prism, you see it’s more than a rainbow; there are little dark lines in the spectrum of the sun.”

The specific spectrum of each star — the light and shadow that it emits — tells cosmologists which direction the star is moving and its chemical composition. By painstakingly plotting the stars within the Milky Way, Newberg and other scientists can produce an accurate three-dimensional model of how stars circulate throughout a galaxy.

That model may reveal the presence of dark matter (matter which has mass, but does not emit light), or it may allow us to dial back time and study the origins of our universe with evidence we cannot gather on Earth.

“Astronomy allows you to explore science beyond our experience here on Earth,” Newberg said. “We can explore regions of different density, composition, and temperature than you can even make on Earth.”

And if you want to study the Milky Way, LAMOST gives you more access to your subject than any other telescope in the world, according to Newberg.

LAMOST is equipped with 4,000 optical fibers — each controlled by separate motors — enabling it to collect more spectra simultaneously than any other telescope. Over the course of a five-year survey, the LAMOST survey will take the spectra of 7.5 million stars. By comparison, during her work on the Sloan Digital Sky Survey, Newberg initiated a survey of 450,000 stellar spectra over four years.

A child’s picture of the Milky Way shows a sphere surrounded by a flat radiating disk of spiral arms. Scientists now know that a diffuse cloud of stars surrounds that picture. Newberg’s primary interest is in that diffuse cloud of stars which, unlike stars within the sphere and spiral arms, were created outside the Milky Way.

Newberg’s past research has shown that small dwarf galaxies are being broken up by the turbulent gravitational tides of the Milky Way and their stars are being swirled through and around the Milky Way. The diffuse cloud of stars around the Milky Way’s disk is thought to have been built up from stars born in smaller galaxies that later merged to create the Milky Way.

“We find stars in these small galaxies that fell into the Milky Way — whether they are intact or not — and know they were not born in our galaxy,” Newberg said. “We’re trying to figure out which stars used to be in the same small galaxy because then we can group them by their family of origin.”

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Inside Rensselaer
Volume 4, Number 10, May 28, 2010
©2010 Rensselaer Polytechnic Institute
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