PHOTOS: Herschel's Coolest Infrared Hotshots
So why is this nebula so incredibly cold? It's actually cooling itself off as it grows, astronomers have found.
As the sun-like star at its center nears the end of its life it expands the nebula with rapidly outpouring gas. That expansion creates a cooling effect - similar to how expanding gas in refrigerators helps keep your ice cream from melting.
The gas in this nebula is traveling much faster than anything in your fridge, though - 500,000 km/hour (310,000 mph).
At one Kelvin the Boomerang nebula is even colder than the coldest known places in our solar system: the permanently-shadowed craters at the moon's south pole that never receive sunlight. Even those pockets of darkness are a balmy 33 Kelvin. (For comparison, water freezes at 273.15 K.)
For that matter, even in the midst of intergalactic space where there's "nothing" is still warmer - the cosmic microwave background glows at a steady 2.8 K.
The new research also shows that the outer edges of the nebula are warming as the outward expansion of gas slows - even though they are still slightly colder than the CMB.
"This is important for the understanding of how stars die and become planetary nebulae," said Sahai. "Using ALMA, we were quite literally and figuratively able to shed new light on the death throes of a Sun-like star."
The Boomerang nebula is located 5,000 light-years from Earth within our Milky Way galaxy.
Source: National Radio Astronomy Observatory press release