Here on SciShow Space, we’re fans of all
things cool and extreme.
We’ve talked about some of the coldest places
in the universe that we know of: manmade laboratories
here on Earth and on the International Space
Station.
But what about the coldest natural place that
we know of?
That’s the Boomerang Nebula -- a dying star
that’s spewing out a cloud of dust and gas.
And by studying it over the past few decades,
astronomers have learned a lot about some
of the weird things that can happen when a
star dies, and what might happen to our very
own Sun in billions of years.
The Boomerang Nebula was first observed in
1980 by an Australian team of astronomers
using a big ground-based telescope.
But it’s pretty far away from us -- head
about 5000 light years in the direction of
the constellation Centaurus and you’re there.
All the astronomers could really see was a
lopsided shape, and they decided it kind of
looked like a boomerang. Which is how the
nebula got its name.
The nebula is actually something called a
pre-planetary nebula, or a low-mass star that’s
near the end of its life.
First, a dying low-mass star will expand outward
and become a red giant.
Then, the outermost molecules will start growing
colder and clumping into dust particles, and
energy from the center of the star pushes
all this gas and dust outward.
Eventually the star will collapse into a hot
white dwarf core that glows because it’s
emitting lots of UV radiation.
The Boomerang Nebula is still in this dusty
cloud of gas phase, but that phase only lasts
for a couple thousand years -- a tiny span
of time, on a universal timescale.
That made it a really interesting target for
astronomers to study.
In the 1990s, a different group of scientists
was observing this strange, asymmetrical nebula
with a radio telescope in Chile.
That’s when they realized just how cold
the Boomerang Nebula was.
They compared radiation signals from vast
empty stretches of space with signals from
carbon monoxide gas particles in the Boomerang
Nebula.
And realized that even though the background
temperature of empty space is cold -- like
around 2.7 or 2.8 Kelvin -- this was even
colder -- at around 1 Kelvin.
Which is just barely above the coldest temperature
possible -- 0 Kelvin, or absolute zero.
But it does kind of make sense that the Boomerang
Nebula would be so cold.
See, temperature is a measure of how much
molecules in a certain area are moving around
-- their kinetic energy.
So when a gas expands and fewer molecules
cover more area, it gets colder.
The Boomerang Nebula is expanding incredibly
quickly and expelling a lot of gas outward
from the star -- at a rate of about 164 kilometers
per second for the past 1,500 years.
That’s about 10 times faster than other
similar gas-spewing space objects.
As the gas expands, the nebula gets colder
-- and it’s hard for the ambient heat of
the universe to seep back in.
Which might explain how the Boomerang Nebula
ended up with the lowest natural temperature
we’ve ever seen.
But its temperature isn’t the only strange
thing about the Boomerang Nebula -- because
it turns out that it isn’t shaped like a
boomerang at all.
In the late 90s, a research group observed
the nebula with the Hubble Space Telescope,
and found that it looked more like a hazy
bow-tie.
Astronomers call this a double-lobe structure,
and many other planetary nebulae end up with
a similar shape because of the gases they’re
expelling.
But then, in 2013, astronomers took a closer
look at the nebula’s shape, using the ALMA
radio telescopes in Chile.
And it turns out that the Boomerang Nebula
is actually a much rounder cloud of expanding
dust and gas.
The bow-tie structure was just a distortion
of the visible light that we could see from
Earth -- there are a lot of small chunks of
dust around the star, which form a kind of
ring that partially obscures the light coming
from the nebula.
That ring was affecting the images from telescopes
like Hubble, making the nebula look more like
a bow tie.
No matter what it’s shaped like, scientists
studying the Boomerang Nebula are hoping to
learn more about how stars die.
Especially because in a few billion years,
our Sun might become a ridiculously cold,
gaseous nebula, too.
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