Researchers with NASA’s New Horizons say they’ve finally been able to determine if space is truly black. The group has posted their work online, and it will soon appear ini the Astrophysical Journal. NPR reports: New Horizons was originally designed to explore Pluto, but after whizzing past the dwarf planet in 2015, the intrepid spacecraft just kept going. It’s now more than four billion miles from home — nearly 50 times farther away from the Sun than the Earth is. That’s important because it means the spacecraft is far from major sources of light contamination that make it impossible to detect any tiny light signal from the universe itself. Around Earth and the inner solar system, for example, space is filled with dust particles that get lit up by the Sun, creating a diffuse glow over the entire sky. But that dust isn’t a problem out where New Horizons is. Plus, out there, the sunlight is much weaker. To try to detect the faint glow of the universe, researchers went through images taken by the spacecraft’s simple telescope and camera and looked for ones that were incredibly boring. Then they processed these images to remove all known sources of visible light. Once they’d subtracted out the light from stars, plus scattered light from the Milky Way and any stray light that might be a result of camera quirks, they were left with light coming in from beyond our own galaxy. They then went a step further still, subtracting out light that they could attribute to all the galaxies thought to be out there. And it turns out, once that was done, there was still plenty of unexplained light. In fact, the amount of light coming from mysterious sources was about equal to all the light coming in from the known galaxies, says Marc Postman, an astronomer with the Space Telescope Science Institute in Baltimore, Maryland. So maybe there are unrecognized galaxies out there, he says, “or some other source of light that we don’t yet know what it is.” […] So where does the light come from? Perhaps, he says, there are far more small, faint dwarf galaxies and other faint regions on the outskirts of galaxies that instruments like the Hubble Space Telescope can’t detect and so scientists just aren’t aware of them. Or, maybe there’s more dust out there interfering with the measurements than scientists expected. Or perhaps there’s a more exotic explanation — some unknown phenomenon out in the universe that creates visible light. It’s even possible it’s something associated with dark matter, a mysterious form of matter that exerts a gravitational pull on visible matter but has never been seen directly.

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