"It is a new measurement, with the capability that we have because we're in a unique place with a camera that can exploit that neat place," Lauer says. "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."īut to do that, Postman notes, it's really essential to understand first how much light there is that needs to be accounted for, and that's where a study such as this one can help. "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," Postman says. 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. Or perhaps there's a more exotic explanation - some unknown phenomenon out in the universe that creates visible light. Or maybe there's more dust out there interfering with the measurements than scientists expected. 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 such as the Hubble Space Telescope can't detect and so scientists just aren't aware of them. Still, he buys the results: "I think the work is really solid." "It's very difficult to turn around and say to the astronomical community, like, 'Hey, guys, we're missing half of the stuff out there,' " Zemcov says. He says for 400 years, astronomers have been studying visible light and the sky in a serious way and yet somehow apparently "missed half the light in the universe." Using fewer images, they made a less precise measurement, but it was still compatible with the current results. "They're saying that there's as much light outside of galaxies as there is inside of galaxies, which is a pretty tough pill to swallow, frankly," notes Michael Zemcov, an astrophysicist at Rochester Institute of Technology, who was not part of the research team.Ī few years ago, Zemcov and some colleagues analyzed New Horizons data in a similar way. The new findings are sure to get astronomers talking. 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." ![]() 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. And it turns out, once that was done, there was still plenty of unexplained light. They then went a step further still, subtracting out light that they could attribute to all the galaxies thought to be out there. 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. Then they processed these images to remove all known sources of visible light. ![]() "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." There's a sprinkling of faint stars, there's a sprinkling of faint galaxies, but it looks random," Lauer says. "The images were all of what you just simply call blank sky. ![]() 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. Plus, out there, the sunlight is much weaker. But that dust isn't a problem out where New Horizons is. 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. 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. It's now more than 4 billion miles from home - nearly 50 times farther away from the sun than the Earth is. New Horizons was originally designed to explore Pluto, but after whizzing past the dwarf planet in 2015, the intrepid spacecraft just kept going. The group has posted its work online, and it will soon appear in The Astrophysical Journal. Now, Lauer and other researchers with NASA's New Horizons space mission say they've finally been able to do it, using a spacecraft that's traveling far beyond the dwarf planet Pluto. It's a tough question that astronomers have tried to answer for decades. Science Pluto Has White-Capped Mountains, But Not Because There's Snow
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