The Coldest Place in the Universe, Galaxy & on Planet Earth (Boomerang Nebula)
Intergalactic emptiness is only 2.725 K, or less than three Kelvin above absolute zero. The Boomerang Nebula, though, is even chillier.
The Cosmic Microwave Background, a remnant of the intense Big Bang, bathes all of space in light that heats anything it comes into contact with up to 2.725 K, including intergalactic space.
The Boomerang Nebula, which has a temperature of just 1 K, is a naturally occurring example of something even colder right here in our own galaxy.
How is it possible for something that exists naturally in the universe to be colder than the universe? It is made possible by the gas’ quick growth.
Intergalactic emptiness is only 2.725 K, or less than three Kelvin above absolute zero. The Boomerang Nebula, though, is even chillier.
The Cosmic Microwave Background, a remnant of the intense Big Bang, bathes all of space in light that heats anything it comes into contact with up to 2.725 K, including intergalactic space.
The Boomerang Nebula, which has a temperature of just 1 K, is a naturally occurring example of something even colder right here in our own galaxy.
How is it possible for something that exists naturally in the universe to be colder than the universe? It is made possible by the gas’ quick growth.
The only thing that would warm you up if you traveled to the darkest regions of intergalactic space and were protected from starlight is the cosmic microwave background, which has a temperature of 2.725 K.
However, the Boomerang Nebula in our own galaxy has a location that is considerably cooler than that.
There are heat sources everywhere in the universe that you can encounter. It gets colder the further you are from all of them. Earth is held at a modest 300 K, 93 million miles from the Sun; without our atmosphere, the temperature would be approximately 50o lower.
The ability of the Sun to heat things up decreases as one travels farther out. For instance, Pluto is just 44 K, which is so cold that liquid nitrogen freezes.
We can even go to far more remote regions of the universe, such as interstellar space, where the nearest stars are light years distant, and discover regions of the universe that are significantly colder, even in our own relatively close-by backyard.
Throughout the galaxy, lone chilly molecular clouds can be found.
They are only 10 to 20 K above absolute zero in temperature, which is even colder than the furthest worlds we can locate in our solar system.
It’s impossible to imagine anything cooler than that inside the Milky Way because stars, supernovae, cosmic rays, stellar winds, and more all contribute energy to the galaxy as a whole.
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The cosmic microwave background will be the only heat source that matters in intergalactic space, millions of light-years from the nearest stars.
Since the Big Bang happened simultaneously everywhere in space, the radiation it left behind simply moves omnidirectionally at the speed of light.
Although that radiation cools as the universe expands, we can still see it today because it has traveled across time and space for around 13.8 billion years before reaching our eyes.
These hardly perceptible photons are the only heat source present at less than 3 oC (5 oF) above absolute zero.
You might believe that 2.725 K is the coldest temperature you can ever experience in nature since every area in the Universe is constantly blasted by these infrared, microwave, and radio photons.
You would have to wait for the Universe to expand further, lengthen the wavelengths of these photons, and cool down to a colder temperature in order to experience something colder.
Of sure, this will take place eventually. In another 13.8 billion years, when the age of the universe is double what it is now, the temperature will only be a single degree above absolute zero.
You can stare right now at a location that is colder than even the darkest regions of intergalactic space.
The Boomerang Nebula is the coldest place in the universe that has been discovered so far. It is a young, still-forming planetary nebula.
You don’t even need to travel somewhere unique! This is our galaxy’s Boomerang Nebula, which is only 5,000 light years away.
It was given the name “Boomerang” because, in 1980, when it was initially discovered from Australia, it appeared to be a two-lobed, asymmetrical nebula.
Better observations have revealed this nebula to be a preplanetary nebula, which is a transitional phase in the life of a dying, Sun-like star.
All Sun-like stars will develop into red giants and pass away in planetary nebulas or white dwarfs, where the outer layers are blown away and the core shrinks to a hot, degenerate condition.
The preplanetary nebula phase, however, comes in between the red giant and planetary nebula phases.
Despite being hotter than the Boomerang Nebula, the preplanetary nebula IRAS 2006+84051 also signifies an interim stage between a red giant and the ultimate planetary nebula/white dwarf stage.
Preplanetary nebulas form before the star’s core temperature rises but after the outer layers start to be ejected.
The ejecta leave the star’s immediate area and go well into the interstellar medium, sometimes in the form of a sphere but more frequently in two bipolar jets.
Only a few of stars, perhaps a dozen, are found to be in this phase. The Boomerang, though, stands out among them. Its gas escapes at a rate 10 times faster than usual, or 164 km/s.
Despite being hotter than the Boomerang Nebula, the preplanetary nebula IRAS 2006+84051 also signifies an interim stage between a red giant and the ultimate planetary nebula/white dwarf stage.
Preplanetary nebulas form before the star’s core temperature rises but after the outer layers start to be ejected.
The ejecta leave the star’s immediate area and go well into the interstellar medium, sometimes in the form of a sphere but more frequently in two bipolar jets.
Only a few of stars, perhaps a dozen, are found to be in this phase.
The Boomerang, though, stands out among them. Its gas escapes at a rate 10 times faster than usual, or 164 km/s.
- Exhale with your mouth wide open, and you’ll feel the warm air gently blow onto your hand.
- Exhale with your lips puckered, making a tiny opening, and that same air feels cold.
In both cases, the air in your body has been warmed, and remains at that high temperature until just before it passes your lips. With your mouth wide open, it simply exits slowly, warming your hand slightly. But with only a tiny opening, the air expands rapidly — what we call adiabatically in physics — and cools as it does so.
The outer layers of the star that’s birthing the Boomerang Nebula possess all of these same conditions:
- a large amount of hot matter,
- being ejected incredibly rapidly,
- from a tiny point (or, more technically, two points),
- that has all the room it could ask for to expand and cool.
It cools much more quickly than the surrounding radiation, including from other stars and the cosmic microwave background, can heat it up.
Although it won’t stay at these cold temperatures forever, but for now, it’s significantly colder than the 2.725 K that sets the effective minimum temperature for everything else in the Universe.
The amazing thing about the Boomerang Nebula is that the very properties it possesses were predicted before it was discovered!
Astronomer Raghvendra Sahai calculated that preplanetary nebulae with just the right conditions — the ones outlined above — could actually achieve a cooler temperature than anything else that naturally occurred in the Universe.
Sahai was then part of the team in 1995 that made the critical long-wavelength observations that determined the temperature of the Boomerang Nebula, and found precisely what was predicted: temperatures lower than any other naturally occurring phenomenon.
As of today, the Boomerang Nebula still stands as the coldest natural place in the Universe.
There’s no doubt that as of right now, of all the locations we’ve ever measured, the Boomerang Nebula possesses the coldest naturally occurring temperatures in all the Universe.
The cause is adiabatic expansion, caused by the rapid expulsion of matter into an environment where it can expand in a relatively uninhibited fashion.
As far as why the Boomerang Nebula is ejecting all this matter so quickly and in such a collimated fashion, however, that’s a controversial and highly active area of research.
So far, the Boomerang Nebula is the only preplanetary nebula that we’ve caught in a phase where its temperature has dropped below that of the Big Bang’s afterglow.
However, there’s no way it’s the only such example of this ever occurring.
There’s likely an even colder place out there than what we’ve discovered so far. We simply have to keep looking.
And who knows? Perhaps, someday, the star at the center of our Solar System — the Sun — will break that record itself, and the remnants of our own Solar System will perhaps become, for a short while, the absolute coldest place in the Universe!
