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When we look into the night sky, it seems that darkness envelops everything around, especially if the sky is overcast and the stars are not visible. Captured by space telescopes and generously shared with the general public, planets, galaxies and nebulae can be seen shining against a backdrop of black, cold space. But is space really black?
According to new research, the universe may not be as dark as astronomers thought. Using the cameras of the automatic interplanetary station New Horizons, which once visited Pluto to measure the darkness of interplanetary space, the researchers concluded that we still have a poor idea of what the universe is.
The results obtained during the study showed that at six billion kilometers from the Sun, far from bright planets and light scattered by interplanetary dust, empty space was about twice as bright as expected.
How dark is space?
For centuries, the darkness of the night sky has been the source of a paradox named after the German astronomer Heinrich Wilhelm Olbers. Presumably, in an infinite static universe, every line of sight ends at a star, so shouldn't the sky look as bright as the sun? Astronomers today know that the universe is 13.8 billion years old and that it is expanding with acceleration. As a result, most of the lines of sight do not end at the stars, but at the fading glow of the Big Bang, and the glow waves are now so expanded that they are invisible to the eye. This is what makes the sky dark. But how dark is the darkness?
Researchers at the National Optical Astronomical Observatory in Arizona studied light in deep space using NASA's New Horizons mission.
The space station New Horizons was launched on January 19, 2006 and flew past Pluto on July 14, 2015. On January 1, 2019, New Horizons flew past Arrocot, formerly called Ultima Thule, one of the countless space icebergs that inhabit the Kuiper belt on the outskirts of the solar system. Today the station is successfully continuing its space travel.
The astronomers' measurements, published in the new study, are based on seven images from the New Horizons long-range reconnaissance thermal imager taken while the station was about 2.5 billion kilometers from Earth. At this distance, the spacecraft found itself far beyond the glow of planets or interplanetary dust, which could potentially affect the quality of images.
“Having a telescope at the very edge of the solar system allows us to ask questions about how dark it really is in space,” write the authors of the paper, published on the Arxiv preprint server. “In the course of our work, we used images of distant objects in the Kuiper belt. Subtract them and any stars, and you will 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 accepts light in a wide spectrum, covering visible and some ultraviolet and infrared waves. The resulting images were then processed - in all images, all light from all sources known to astronomers was removed, including any relatively nearby stars.
By processing the obtained images, the researchers also removed the light emanating from galaxies, which, as the authors of the scientific work believe, exist, but have not yet been detected. As a result, deep space images were obtained without any light pollution. Interestingly, even though all light sources (both known and unknown) have been removed, there is still a lot of light in the resulting images. Where exactly the remaining light comes from is unknown.
Researchers believe that light may come from as-yet undiscovered stars or galaxies. However, it cannot be ruled out that the light in the resulting images may be something completely new. More research will undoubtedly be conducted as scientists continue to search for sources of light pollution, but the source of additional light photons remains a mystery today.
According to Dan Hooper, a physicist at the Fermi National Accelerator Laboratory in Batavia, he has suggested that mysterious dark matter is the culprit for the additional illumination. In an email to The New York Times, he said that he and his colleagues, pondering a possible light source, had never come up with any new physics to explain its presence in the images, "except for a few really unattractive options."
It is believed that the Universe is filled with "dark matter", the exact content of which is unknown, but the gravity of which forms the space visible to us. According to some theories, this matter could be clouds of exotic subatomic particles that decay radioactively or collide and annihilate in bursts of energy that add light to the universal glow. Another possible clue could be a common mistake.
According to the authors of the study, the possibility that astronomers were mistaken and missed the light source exists, the truth is only 5%. Well, hopefully future research can shed light on this dark patch of near space.