The Universe’s Background Starlight is Twice as Bright as Expected
upstart writes:
The universe's background starlight is twice as bright as expected:
Even when you remove the bright stars, the glowing dust and other nearby points of light from the inky, dark sky, a background glow remains. That glow comes from the cosmic sea of distant galaxies, the first stars that burned, faraway coalescing gas - and, it seems, something else in the mix that's evading researchers.
Astronomers estimated the amount of visible light pervading the cosmos by training the New Horizons spacecraft, which flew past Pluto in 2015, on a spot on the sky mostly devoid of nearby stars and galaxies (SN: 12/15/15). That estimate should match measurements of the total amount of light coming from galaxies across the history of the universe. But it doesn't, researchers report in the March 1 Astrophysical Journal Letters.
"It turns out that the galaxies that we know about can account for about half of the level we see," says Tod Lauer, an astronomer at the National Science Foundation's NOIRLab in Tucson, Ariz.
[...] While Lauer's group previously noted a discrepancy, this new measurement reveals a wider difference, and with smaller uncertainty. "There's clearly an anomaly. Now we need to try to understand it and explain it," says coauthor Marc Postman, an astronomer at the Space Telescope Science Institute in Baltimore, Md.
There are several astronomical reasons that could explain the discrepancy. Perhaps, says Postman, rogue stars stripped from galaxies linger in intergalactic space. Or maybe, he says, there is "a very faint population of very compact galaxies that are just below the detection limits of Hubble." If it's the latter case, astronomers should know in the next couple years because NASA's recently launched James Webb Space Telescope will see these even-fainter galaxies (SN: 10/6/21).
Another possibility is the researchers missed something in their analysis. "I'm glad it got done; it's absolutely a necessary measurement," says astrophysicist Michael Zemcov of the Rochester Institute of Technology in New York who was not involved in this study. Perhaps they're missing some additional glow from the New Horizons spacecraft and its LORRI instrument, or they didn't factor in some additional foreground light. "I think there's a conversation there about details."
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