Why is outer space not as dark as we think?

When we look at the night sky, it seems that the darkness envelops everything around us, especially if the sky is covered with clouds and no stars are visible. In images taken with space telescopes and generously shared with the public, planets, galaxies and nebulae can be seen flaunting the black, cold space. But is space really black? The universe may not be as dark as astronomers thought, according to a new study. With the help of cameras from the robot space station New Horizons, which once visited Pluto to measure the darkness in interplanetary space, scientists have come to the conclusion that we still have a bad idea of ​​what the universe is. The results of the study showed that six billion kilometers from the sun, away from bright planets and light scattered by interplanetary dust, the empty space was about twice as bright as expected.

The interplanetary space station New Horizons explores outer space.

How dark is it in space?

For centuries, the darkness of the night sky has been the source of a paradox named after the German astronomer Heinrich Wilhelm Olbers. Probably, in an infinitely static universe, every line of sight ends at a star, so shouldn’t the sky look as bright as the sun? Today, astronomers know that the universe is 13.8 billion years old and is expanding at an accelerating pace. As a result, most lines of sight do not end in the stars, but in the fading glare of the Big Bang, and the light waves are now so expanded that they are invisible to the eye. That’s what makes the sky dark. But how dark is the darkness?

Researchers at the National Optical Astronomical Observatory in Arizona studied light in space with NASA’s New Horizons mission. The New Horizons spacecraft was launched on January 19, 2006 and flew past Pluto on July 14, 2015. On January 1, 2019, New Horizons flew past Arrokoth, formerly Ultima Thule, one of the countless cosmic icebergs found in the Kuiper Belt on the edge of the solar system. Today, the station successfully continues its space journey.

Overview of the solar system and Kuiper belt objects. The yellow line shows the trajectory of the New Horizons mission.

The team of astronomers’ measurements, published in the new study, are based on seven images from New Horizon’s long-range reconnaissance thermal imager, taken at a time when the station was about 2.5 billion kilometers from Earth. At this distance, the spacecraft was far beyond planetary glow or interplanetary dust, which could potentially affect image quality.

“Having a telescope on the edge of the solar system allows us to ask questions about how dark it really is in space,” the authors of the magazine, published on the Arxiv preprint server, write. “In our work, we used images of distant Kuiper belt objects. Subtract them and any stars and you have a clear sky. “

Photos from NASA’s New Horizons mission

According to The New York Times, the New Horizons camera is a “white light shaper” that receives light in a wide range, including visible and certain ultraviolet and infrared waves. The resulting images were then processed – in all images, all light was removed from all sources known to astronomers, including all relatively nearby stars.

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By processing the images obtained, the scientists also removed the light that comes from galaxies, which, as the authors of the scientific work believe, exist, but which have not yet been discovered. The result was images of deep space without any light pollution. Interestingly, despite the removal of all light sources (both known and unknown sources), there is still a lot of light in the resulting images. Exactly where the remaining light comes from is unknown.

Today, scientists estimate the number of galaxies in the observable universe at two billion.

Scientists believe that light may come from as yet undiscovered stars or galaxies. However, it can not be ruled out that the light in the resulting images may be something completely new. Undoubtedly, more research will be done as researchers continue to look for sources of light pollution, but so far the source of the extra light photons is a mystery.

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According to Dan Hooper, a physicist at the Fermi National Accelerator Laboratory in Batavia, the mysterious dark matter is the culprit for the extra lighting. In an email to The New York Times, he said that he and his colleagues, while pondering the possible light source, have not come up with any new physics that can explain its presence in the pictures, “except for some really unattractive alternatives.”

It is believed that the universe is full “dark matter”, whose exact content is unknown, but whose gravity shapes the cosmos we see. According to some theories, this matter can be clouds of exotic subatomic particles that decay radioactively or collide and destroy in energy bursts that add light to the universal radiance. Another possible clue may be a common mistake. According to the authors of the study, there is a possibility that astronomers made a mistake and missed the light source, even if it is only 5%. Well, we hope that future research will shed light on this dark region of near space.

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