2026年3月托福机经套卷(第2套) - Read an Academic Passage Q3

The Mystery of Dark Galaxies Ultraviolet (UV) astronomy has unveiled numerous cosmic phenomena. An especially intriguing discovery is that of dark galaxies. Unlike typical galaxies (gravitationally bound systems of stars, gas, and other particles), dark galaxies emit little to no visible light, making them nearly impossible to detect using conventional optical telescopes. However, these galaxies emit UV radiation, providing astronomers with a unique window to study them. Dark galaxies challenge our understanding of galaxy formation. Traditional models suggest that galaxies form through gas accumulation and star formation. But although dark galaxies contain vast amounts of gas, they have few, if any, stars. This raises questions about the processes that inhibit star formation. Some researchers propose that turbulence within the gas clouds might prevent the gas from collapsing to form stars. Observations from the Hubble Space Telescope and other UV-sensitive instruments have revealed that dark galaxies were more common in the early universe. These findings suggest that dark galaxies may represent a primordial phase in galaxy evolution. One hypothesis is that high levels of UV radiation in the early universe prevented the gas in dark galaxies from cooling and condensing into stars. Observations of regions with high UV radiation support this theory.