How bright is the universe’s glow? Study offers best measurement yet | Science & Technology

The new study, published Aug. 28 in The Astrophysical Journal, draws on observations from NASA’s New Horizons spacecraft, which whizzed past Pluto in 2015 and is now nearly 5.5 billion miles from Earth. The research seeks to answer a deceptively simple question, said co-author Michael Shull, an astrophysicist at the University of Colorado Boulder.

“Is the sky really dark?” said Shull, professor emeritus in the Department of Astrophysical and Planetary Sciences.

Space may look black to human eyes, but scientists believe that it’s not completely dark. Since the dawn of the cosmos, trillions of galaxies containing countless stars have formed and died, leaving behind an imperceptibly faint light. Think of it as the night light in space.

Shull and the team, led by Marc Postman at the Space Telescope Science Institute in Baltimore, calculated just how bright that glow is. Their findings suggest that the cosmic optical background is roughly 100 billion times fainter than the sunlight that reaches Earth’s surface¬ — far too faint for humans to see with the naked eye.

The results could help scientists shine a light on the history of the universe since the Big Bang.

“We’re kind of like cosmic accountants, adding up every source of light we can account for in the universe,” Shull said.

Into the dark

It’s a type of number crunching that has captured the imagination of scientists for nearly 50 years, he added.

Shull explained that, after decades of research, astrophysicists think they have a pretty good idea of how the cosmos evolved. The first galaxies formed during an epoch known as the Cosmic Dawn several hundred million years after the Big Bang. The starlight from galaxies in the distant universe reached its brightest point about 10…