Challenging Past Assumptions: Light From Outside Our Galaxy Much Brighter Than Expected

Scientists at RIT lead a study utilizing data collected by LORRI (Long Range Reconnaissance Imager) on NASA’s New Horizons mission.

Researchers at Rochester Institute of Technology have conducted a study with new measurements that show the light emitted by stars outside our galaxy is two to three times brighter than the light from known populations of galaxies. These findings challenge previous assumptions about the number and environment of stars in the universe. The results of the study have been accepted for publication in The Astrophysical Journal and are currently available on ArXiv.

The research team analyzed hundreds of images of background light taken by the Long-Range Reconnaissance Imager (LORRI) on NASA’s New Horizons mission to calculate the cosmic optical background (COB)—the sum of light emitted by stars beyond the Milky Way over the history of the universe. If the COB brightness doesn’t equal the light from galaxies we know about, it suggests there might be missing sources of optical light in the universe.

Excess Light Beyond Known Galaxies

“We see more light than we should see based on the populations of galaxies that we understand to exist and how much light we estimate they should produce,” said Teresa Symons ’22 Ph.D. (astrophysical sciences and technology), who led the study for her dissertation and is now a postdoctoral researcher at the University of California Irvine. “Determining what is producing that light could change our fundamental understanding of how the universe formed over time.”

Earlier this year, an independent team of scientists reported the COB was twice as large as originally believed in Astrophysical Journal Letters. Those results were no fluke, as corroborated using a much broader set of LORRI observations in the new study by Symons, RIT Associate Professor Michael Zemcov, and researchers at the Jet Propulsion Laboratory at Caltech, UC Irvine, UC Berkeley, and Johns Hopkins University.

While an unobscured measurement of the COB is difficult to achieve from the Earth due to dust between planets, the New Horizons spacecraft is at the edge of our solar system where this foreground is minimal and provides a much clearer view for this type of study. The scientists hope that future missions and instruments can be developed to help explore the discrepancy.

“This has gotten to the point where it’s an actual mystery that needs to be solved,” said Zemcov, a research professor at RIT’s Center for Detectors and School of Physics and Astronomy. “I hope that some of the experiments we’re involved in here at RIT including CIBER-2 and SPHEREx can help us resolve the discrepancy.”

Reference: “A Measurement of the Cosmic Optical Background and Diffuse Galactic Light Scaling from the R < 50 AU New Horizons-LORRI Data” by Teresa Symons, Michael Zemcov, Asantha Cooray, Carey Lisse, Andrew R. Poppe, 14 December 2022, ArXiv.
DOI: 10.48550/arXiv.2212.07449

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