Think of the coldest day you've ever lived through. Now picture somewhere so cold that it makes Antarctica's worst winter feel like a summer afternoon. Out in deep space, there's a place colder than space itself, and it's hiding inside a glowing cloud shaped like an hourglass.
It's called the Boomerang Nebula, and it's the coldest natural place currently known. Parts of it have cooled to about 1 kelvin, roughly minus 458 degrees Fahrenheit. That's just one degree above absolute zero and even colder than the faint leftover glow of the Big Bang that fills all of space.
How Cold Is Space, Anyway?
Absolute zero is the coldest temperature possible, about minus 459.67 degrees Fahrenheit. Scientists measure super-cold things in kelvins, a scale that starts at absolute zero. Nothing can actually reach it, though things can get very close.
Space isn't quite that cold. The whole universe is bathed in a faint afterglow from the Big Bang called the cosmic microwave background. It has a temperature of about 2.7 kelvins, or around minus 455 degrees Fahrenheit, and it's slowly getting colder as the universe expands. For a long time, that was considered the background chill of the cosmos.
A Nebula Colder Than Space
The Boomerang Nebula sits about 5,000 light-years away in the constellation Centaurus. Astronomers who looked at it in 1979 named it after the boomerang because of its shape. It's a young cloud of gas and dust forming around an old star near the end of its life.
In a 1997 study, astronomers Raghvendra Sahai and Lars-Åke Nyman measured the gas flowing out of it. They found that parts of the nebula were colder than the cosmic background radiation around it. It was a striking discovery: a spot in space colder than space itself.
The Secret Is Speed
How can a cloud get colder than its surroundings? The answer is expansion. The dying star at its center is blowing gas outward at about 310,000 miles per hour, and it has been doing so for roughly 1,500 years. When gas expands rapidly, it cools down.
You've felt a tiny version of this yourself. When you spray an aerosol can for a while, the can gets cold in your hand. The Boomerang Nebula is doing something similar on a gigantic scale.
The Real Record Is on Earth
Here's the twist. The coldest places in the universe that we know of aren't in space at all. They're in laboratories built by people. Scientists have chilled atoms to about 38 trillionths of a degree above absolute zero, far colder than any nebula.
People have been chasing extreme cold for more than a century. In 1908, Dutch physicist Heike Kamerlingh Onnes became the first person to turn helium into a liquid, reaching about minus 452 degrees Fahrenheit. By lowering the pressure, he got down to around 1.5 kelvins, and the achievement helped earn him a Nobel Prize in 1913.
There's even a super-cold lab in orbit. NASA's Cold Atom Laboratory launched to the International Space Station in 2018. In weightlessness, it can create clouds of atoms colder than those made in labs on the ground.
So the coldest natural spot we know of is a distant cloud 5,000 light-years away, but the all-time champion may be a carefully guarded box of atoms on our own planet. Next time winter feels brutal, at least you'll know it could be a whole lot worse.
