ANYONE looking for the coolest hang-out in outer space should set their
sights on the Boomerang Nebula. The temperature in the nebula鈥檚 outer regions is
less than 3 kelvin鈥攖he lowest ever measured, apart from temperatures
created cryogenically in laboratories.
The Boomerang is a cloud of gas and dust ejected by a dying star. As it
expands at over 150 kilometres per second, it cools 鈥渂y the same physical
process that cools the insides of domestic refrigerators鈥�, says Raghvendra Sahai
of the Jet Propulsion Laboratory in Pasadena, California.
With Lars-Ake Nyman of the Onsala Space Observatory in Sweden, Sahai studied
the nebula at submillimetre wavelengths using a telescope in Chile. This
revealed that the gas is absorbing the cosmic microwave background, a sea of
radiation left over from the big bang. The gas could only absorb this if it is
chilled to less than 3 K. The results will appear in Astrophysical Journal
Letters.
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