Boomerang Nebula: The Coldest Natural Spot in the Universe

Astronomers have identified the Boomerang Nebula, a fast-expanding shell around a dying star about 5,000 light-years away, as the coldest natural object known at roughly one degree above absolute zero—colder than the cosmic microwave background of 2.7 K. The extreme chill arises from rapid gas expansion acting like a refrigerator, and the temperature was inferred from how the gas absorbs background radiation. This is a transient stage in a Sun-like star’s death, and the outer gas will warm over time; no colder natural places have been found yet.