The Coldest Place in the Universe

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A Real-life "Frozen" Realm in Space

The Boomerang Nebula as seen by the Hubble Space Telescope. NASA/ESA/STScI

We all know space is cold, much colder than we have it here on Earth (even at the poles). Most people think that space is absolute zero, but it's not. Astronomers have measured its temperature at 2.7 K (2.7 degrees above absolute zero). But, it turns out that there's an even colder space, in a place you wouldn't think to look: in a cloud surrounding a dying star.  It's called the Boomerang Nebula, and astronomers have measured its temperature at an astounding 1 K (0272.15 C or 0457.87 F). 

Freezing a Nebula

How did the Boomerang get so cold? This nebula is what's called a "pre-planetary" nebula, which means that it is a cloud of dust, mixed with gases "exhaled" away from the aging star at its heart. At some point, the star will become a white dwarf, emitting high amounts of ultraviolet radiation. That will cause the surrounding cloud to heat up and glow. This is the way our Sun will ultimately die. For now, however, the gases being lost by the star are expanding rapidly into space. As they do, they cool very quickly and that's how it got down to 1 degree above absolute zero.

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A Radio View of the Boomerang

The Boomerang Nebula, as seen by the ALMA radio telescope array. ALMA/NRAO

Researchers using the Atacama Large Millimeter Array (a radio telescope array in Chile that studies such things clouds of dust around other stars), have also studied the nebula to understand why it looks like a ghostly "bow tie".  Their radio image showed an even eerier-looking "ghost at the heart of the nebula, made mostly of cool gas and dust grains. 

Forming a Planetary Nebula

Astronomers are getting a better handle on what happens when Sun-like stars begin to die. In about 5 billion years or so, the Sun will begin the same process. Long before it dies, it will start to lose gases from its outer atmosphere. Inside the Sun, the nuclear furnace that powers our star will run out of hydrogen fuel and begin to burn helium, and then carbon. Each time it switches fuels, the Sun will heat up, and it will turn into a red giant. Eventually, it will begin to contract and transform into a white dwarf.

The ultraviolet radiation from our shrunken, but very bright Sun, will heat up the clouds of gas and dust around it, and distant viewers will see it as a planetary nebula. Its inner planets will be gone, and the outer solar system worlds might have a chance at supporting life for a while. But, eventually, billions of years from now, the solar white dwarf will cool down and fade away. 

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Other Cold Places in the Universe

An artist's conception of the frigid surface of Pluto. SWRI

It's possible that other dying stars are exhaling clouds of gas and dust, and that those nebulae could be cold, too. Still, there are other cold places to study, although none so cold as the Boomerang. For example, the icy world Pluto gets down to 44K, which is -369 F (-223 C). Still much warmer than the Boomerang!  Other clouds of gas and dust, called dark nebulaeare even colder, than Pluto, at only 7 to 15 degrees K (-266.15 to  -258 C, or -447 to -432 F)'

In the first panel, we learned space is 2.7 K. That's the temperature of the microwave background radiation — a remnant of radiation left over from the Big Bang. The outer edges of Boomerang actually absorb heat from interstellar space, and perhaps from the ultraviolet radiation of its dying star. But, deep in the center of the nebula, things remain colder than space, and so far, it's the coldest known spot in the cosmos!

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Your Citation
Petersen, Carolyn Collins. "The Coldest Place in the Universe." ThoughtCo, Aug. 27, 2020, Petersen, Carolyn Collins. (2020, August 27). The Coldest Place in the Universe. Retrieved from Petersen, Carolyn Collins. "The Coldest Place in the Universe." ThoughtCo. (accessed January 26, 2021).