Boomerang Nebula – the coolest place in the Universe?
The Boomerang Nebula is a young planetary nebula and
the coldest object found in the Universe so far. The NASA/ESA Hubble
Space Telescope image illustrates how Hubble’s keen vision reveals
surprises in celestial objects.
This NASA/ESA Hubble Space Telescope image shows a young planetary
nebula known (rather curiously) as the Boomerang Nebula. It is in the
constellation of Centaurus, 5000 light-years from Earth. Planetary
nebulae form around a bright, central star when it expels gas in the
last stages of its life.
The Boomerang Nebula is one of the Universe’s peculiar places. In 1995,
using the 15-metre Swedish ESO Submillimetre Telescope in Chile,
astronomers revealed that it is the coldest place in the Universe found
so far. With a temperature of -272 C, it is only 1 degree warmer than
absolute zero (the lowest limit for all temperatures). Even the -270 C
background glow from the Big Bang is warmer than this nebula. It is the
only object found so far that has a temperature lower than the
background radiation.
Keith Taylor and Mike Scarrott called it the Boomerang Nebula in 1980
after observing it with a large ground-based telescope in Australia.
Unable to see the detail that only Hubble can reveal, the astronomers
saw merely a slight asymmetry in the nebula’s lobes suggesting a curved
shape like a boomerang. The high-resolution Hubble images indicate that
‘the Bow tie Nebula’ would perhaps have been a better name.
The Hubble telescope took this image in 1998. It shows faint arcs and
ghostly filaments embedded within the diffuse gas of the nebula’s
smooth “bow tie” lobes. The diffuse bow-tie shape of this nebula makes
it quite different from other observed planetary nebulae, which
normally have lobes that look more like “bubbles” blown in the gas.
However, the Boomerang Nebula is so young that it may not have had time
to develop these structures. Why planetary nebulae have so many
different shapes is still a mystery.
The general bow-tie shape of the Boomerang appears to have been created
by a very fierce 500 000 kilometre-per-hour wind blowing ultracold gas
away from the dying central star. The star has been losing as much as
one-thousandth of a solar mass of material per year for 1500 years.
This is 10-100 times more than in other similar objects. The rapid
expansion of the nebula has enabled it to become the coldest known
region in the Universe.
The image was exposed for 1000 seconds through a green-yellow filter.
The light in the image comes from starlight from the central star
reflected by dust particles.
