When you look up at the night sky, space may seem like a vast expanse of darkness. But are some regions darker than others? Where are the darkest places in the solar system, and on a larger scale, the universe?
So the answer isn’t easy and depends on who you ask, experts told Live Science.
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Andreas Burkert, a theoretical astrophysicist at the University of Munich, told Live Science that darkness also “depends on how you define it.” The visible light spectrum illuminates several places in the universe. However, other wavelengths on the electromagnetic spectrum, such as gamma rays and ultraviolet light, affect almost everything. This means that the universe is extremely bright across the electromagnetic spectrum.
low albedo
If only visible light is considered, there are some places in the universe that are very dark. Various factors contribute to this darkness.
First, space objects can appear very dark because they are made of materials that absorb light. Scientifically, this is known as albedo, or the amount of light reflected from a surface. For example, a perfect mirror reflects 100% of the light directed at it and has an albedo of 1, while charcoal has an albedo of 4%.
According to Guinness World Records, the core of comet Boreli (also known as 19P/Boreli) is one of the darkest spots in the solar system. Images taken in 2001 show that the comet is 5 miles (8 kilometers) long, made of dust and ice, and reflects less than 3% of sunlight.
Similarly, TrES-2 b, the darkest known exoplanet in the universe, has a light reflectance of less than 1%, which is thought to be due to its atmosphere containing large amounts of sodium vapor and gaseous titanium oxide. In contrast, Earth reflects about 30% of the sun’s light.
Black holes are also dark because they capture light that crosses the event horizon. But interestingly, “that doesn’t mean there’s no light,” Burkert says. “It’s just trapped.” As a result, “when you go into the black hole, it actually becomes very bright,” he explained.
Block out light and distant objects
Darkness can also exist if something blocks the light from a nearby star. For example, some craters located at the moon’s poles receive no sunlight at all. These locations are very dark because they are in “perpetual shadow,” Postman said. Pluto’s shadowy craters can also be very dark due to their distance from the Sun.
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Far beyond that, dense dust clouds called molecular cores or bok globules are also thought to be pitch black. They look like “holes in the sky,” Burkhart said. This is because the globules are made of a mixture of hydrogen molecules, carbon oxide, helium, and silicate dust, which block nearly all visible light from the surrounding stars, causing them to disappear. But this light blocking is less severe in the infrared spectrum, said Burkert, who studied Barnard 68, a globule about 500 light-years from Earth.
Finally, there are parts of the sky that are dark simply because they are far away from the light source. These locations were recorded by NASA’s New Horizons telescope, which was sent to take pictures of the outer corners of the galaxy.
Based on a 2021 paper published in The Astrophysical Journal, these distant regions are extremely faint. “On average, the sky outside is 10 times darker than the sky near Earth,” said Postman, a co-author of the study. However, in these areas there was still light from the cosmic background glow.
Burkert pointed out that Earth’s position in the relatively dark cavity of the Milky Way gives us a unique, unobstructed view into the far reaches of space.
“We’re sitting in the middle of this big bubble, so we can see a lot of stars,” Burkhart said. “If we weren’t in a bubble, astronomy probably wouldn’t have developed. [darkness] I think this is a very relevant and important idea and question. ”
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