Spaceflight Insider

Probe finds deep space is not completely dark

NASA’s New Horizons spacecraft, now 50 AU (astronomical units) from the Sun. Image Credit: NASA

Now more than four billion miles away from Earth, NASA’s New Horizons spacecraft, acting as a distant space observatory, has found that deep space is not entirely dark.

At 48.9 times farther from the Sun than the Earth, New Horizons is far enough away from any major sources of light, putting it in an ideal position to identify tiny light sources from the universe.

Scientists have long wondered whether space is completely dark. Astronomer Tod Lauer of the National Science Foundation‘s (NSF) National Optical-Infrared Astronomy Research Laboratory (NOIRLab), said he always questioned whether the universe “puts out a glow” independent of all known visible light sources, such as stars and galaxies. This glow is known as the Cosmic Optical Background (COB).

The question of whether this glow exists cannot be answered from observations in the inner solar system or from Earth because there the whole sky has a glow produced by dust particles the Sun lights up.

However, in the region where New Horizons is traveling, sunlight is very weak, and far less dust is present, making this an ideal location to search for evidence of a glow emitted by the universe.

In an effort to detect such a glow, scientists analyzed archival images of areas with very few stars and very faint galaxies collected by New HorizonsLong Range Reconnaissance Imager (LORRI). They then processed the images to remove all known light sources, including light from stars, light scattered by the Milky Way galaxy, and light from distant galaxies.

“The images were all of what you just simply call blank sky. There’s a sprinkling of faint stars; there’s a sprinkling of faint galaxies, but it looks random. What you want is a place that doesn’t have many bright stars in the images or bright stars even outside the field that can scatter light back into the camera,” Lauer explained.

Researchers analyzed these fields imaged by LORRI. Image Credit: Tod Lauer et al.

When all known light sources were subtracted out, the images still contained light though not from any known source. According to astronomer Marc Postman of the Space Telescope Science Institute (STScI) in Baltimore, the amount of light still seen in the images is approximately the same amount that comes from known galaxies.

The light could be coming from as-yet undiscovered distant galaxies or from a completely unknown source, Postman said. It is also possible that deep space has more dust than scientists thought, and that that dust is affecting the measurements.

Or the light could be coming from an as-yet unknown exotic source, possibly even something associated with the mysterious dark matter, which gravitationally influences visible matter but itself has never been seen.

Knowing just how dark deep space is will provide scientists with important insights into the formation, history, and evolution of the universe.

Astrophysicist Michael Zemcov of the Rochester Institute of Technology (RIT) made similar findings several years ago, also using New Horizons images.

“As a person who studies the universe, I really want to know what the universe is made of and what are all the components of the universe. We would like to think that the components that give off light are something that we can really get a good sense of and understand why there is that much light,” Postman said.



Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.

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