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Researchers measured the intensity of the universe's ultraviolet background radiation, and say it may be strong enough to strip small galaxies of star-forming gas. Christopher Intagliata reports. 

据克里斯托弗·因塔利亚塔(Christopher Intagliata)报道,研究人员测量了宇宙紫外线背景辐射的强度,并指出它的高强度可能破坏形成恒星前期的星云气体


撰文\播音:克里斯托弗·因塔利亚塔(Christopher Intagliata




The sun spews out ultraviolet radiation—that's why you put on sunscreen. But the sun isn't the only UV-producing celestial body. "Stars and supermassive black holes produce a huge amount of UV radiation." Michele Fumagalli, an astrophysicist at Durham University in the U.K. "And some of this radiation can escape a galaxy, and so this radiation builds up this cosmic UV background."

太阳放射紫外线这也是你要擦防晒霜的原因但是太阳并不是唯一产生紫外线的天体。米歇尔·富马加利(Michele Fumagalli)是英国达勒姆大学的天体物理学家,他说:恒星和超大质量的黑洞会产生大量紫外线辐射。一些辐射会逃离星系,构成了宇宙的紫外线背景。


That cosmic UV background permeates the universe. But it's diffuse—meaning hard to measure, especially from here on Earth. "And so the way we do this measurement is with a little trick." That is, when UV radiation hits gas, it gives off a red glow. So Fumagalli and his team used what’s called the MUSE instrument at the Very Large Telescope in Chile to stare—for hours—at the edge of a superthin galaxy, until they saw that red glow.



And since they knew how much gas was there, they were able to calculate the intensity of the UV radiation hitting the gas—the cosmic UV background. The finding is in the Monthly Notices of the Royal Astronomical Society. [Michele Fumagalli et al., A measurement of the z = 0 UV background from Hα fluorescence]



That calculation offered clues to another celestial mystery: why we don't see as many small galaxies in the universe as theory would predict. Fumagalli says the UV background radiation might strip away valuable star-forming gas from the small guys. 



"This is what happens to the small galaxies in the universe. They have gas, which is what's needed to form stars. But if that gas is exposed to intense UV radiation, essentially it evaporates. Which means the galaxies lose their supply of fuel to make new stars. Meaning they don't shine and we do not see them."



So the small galaxies remain dark. But bigger galaxies have a much smaller surface-to-volume ratio of star-forming gas—imagine a whole ocean of water compared to a tiny glassful. UV radiation can't strip away all the gas. So stars form. Like our sun. Which, when it comes to ultraviolet rays here on Earth, is still the star of the show.




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