University of Pittsburgh
January 13, 2005

Pitt, Sloan Digital Sky Survey Research Illuminates How Stars, Galaxies Form

Largest-ever look at the sky confirms theory of gravity's role in shaping universe
Contact:  412-624-4147

PITTSBURGH—Researchers at the University of Pittsburgh and other institutions participating in the Sloan Digital Sky Survey (SDSS) have found evidence confirming the role of gravity in the formation of stars and galaxies, they announced Jan. 11 at a meeting of the American Astronomical Society in San Diego.

Their paper, titled "Detection of the Baryon Acoustic Peak in the Large-Scale Correlation Function of SDSS Luminous Red Galaxies," submitted to the Astrophysical Journal, provides confirmation for the cosmological theory of structure formation: Small irregularities in how matter is distributed throughout the universe gravitationally attract and accumulate nearby matter, eventually forming stars, galaxies, and clusters of galaxies.

"It's a confirmation of the basic picture that we have of how the universe went from its early stages, where the distribution of matter and energy was very, very uniform, to the universe we see today, where there are lots of clusters of galaxies spread across the sky," said Ryan Scranton, a postdoctoral fellow in the Department of Physics and Astronomy in Pitt's School of Arts and Sciences and one of the paper's coauthors, along with Andrew Connolly, an associate professor in the Department of Physics and Astronomy.

The researchers, led by Daniel Eisenstein of the University of Arizona, studied ripples in the distribution of matter throughout the universe that are caused by the disparity between normal matter and "dark matter": The first interacts with light, while the second does not. Last year, a survey of cosmic microwave background (CMB) clearly showed such ripples. But in order to confirm that the same effect was taking place with galaxies, researchers needed to observe a larger volume of the universe than previous galaxy surveys contained. The SDSS was able to solve this problem with its unique combination of multicolor imaging and spectroscopy, which targeted a population of distant, luminous galaxies over a wide area of the sky.

"The CMB told us that the light, the energy in the early universe that was bound up in photons and radiation, was displaying this rippling behavior," said Scranton. "With this galaxy survey, we have confirmation that the regular matter was doing the same thing."

He added, "It happened exactly where we expected to see it, and the signal looked like what we expected to see, so it gives every indication that our theories for how matter and energy have organized themselves via gravity throughout the history of the universe are in the right ballpark."

The paper is available online at, and the official SDSS news release is available at

The SDSS is managed by the Astrophysical Research Consortium for the participating institutions, including the University of Pittsburgh. A complete list of institutions and authors may be found at