New Study Confirms the Light From Outside Our Galaxy Is Brighter Than Expected

Artist's impression of NASA's New Horizons spacecraft.

Artist's impression of NASA's New Horizons spacecraft. (Image: NASA/APL/SwRI and NASA/JPL-Caltech)

Scientists analyzed new measurements showing that the light emitted by stars outside our galaxy is two to three times brighter than the light from known populations of galaxies, challenging assumptions about the number and environment of stars in the universe.

Results of the study led by researchers at Rochester Institute of Technology have been posted to ArXiv and accepted for publication in The Astrophysical Journal.

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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.

There is more background light in the universe than we can account for

If the COB brightness doesn’t equal the light from galaxies we know about, it suggests there might be missing optical light sources in the universe. 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, said:

“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. Determining what produces that light could change our understanding of how the universe formed over time.”

Earlier this year, an independent team of scientists reported the COB was twice as large as initially 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 challenging 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. Zemcov, a research professor at RIT’s Center for Detectors and School of Physics and Astronomy, said:

“This has gotten to the point where it’s an actual mystery that needs to be solved. So 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.”

Provided by  Luke Auburn, Rochester Institute of Technology [Note: Materials may be edited for content and length.]

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