As for the coldest natural place in the universe, scientists have found that, too. It’s a location that, amazingly enough, manages to be chillier than space; a thermometer would read less than the 2.73 K temperature of the CMB. It’s the Boomerang Nebula.
When observing the Boomerang, we actually view the first stages of a planetary nebula. Ironically, such objects are usually extremely hot because their central star is typically fiercely blue (the hottest type of star); the surface temperature of this sun is 10 times that of our Sun and sends sizzling ultraviolet radiation spewing outward to excite the surrounding gases.
But the Boomerang Nebula is so young that it expels gas at a furious pace. This outrush not only blocks the cosmic microwaves that might otherwise warm it, but it also carries heat away. Even in normal terrestrial life, we see examples of how expanding gas has a chilling effect — discharging a can of whipped cream or tire-inflation gas makes that container feel colder in your hand.
Here in the constellation Centaurus, an impressive 5,000 light-years away, the newly minted planetary nebula expands so rapidly that the Boomerang has a temperature of only –458° F (–272° C), a mere 1° above absolute zero. This is the only known object whose temperature is naturally lower than the background radiation of the universe.
Astronomers using the 15-meter scope at the European Southern Observatory in Chile made this discovery in 1995. They would have liked to give it a better name, as “Boomerang” didn’t seem relevant either to the concept of cold or to the object’s appearance. The unfortunate-but-catchy label originated when astronomers Keith Taylor and Mike Scarrott observed the nebula 15 years earlier using a modest telescope in Australia. The pair only saw the brightest sections of its curving gases, and, being Australian, the aboriginal weapon was their Rorschach response.