HEIC0301: EMBARGOED UNTIL: 12:00 (CET) 20 February, 2003

Photo release:
Boomerang Nebula - the coolest place in the Universe?

20-February-2003 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 Sahai and Nyman revealed that it is the coldest place in 
the Universe found so far. With a temperature of -272ºC, it is only 1 
degree warmer than absolute zero (the lowest limit for all 
temperatures). Even the -270ºC 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.

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Notes for editors
The Hubble Space Telescope project is an international cooperation 
between ESA and NASA.

The original Hubble image was obtained by R. Sahai and J. Trauger (Jet 
Propulsion Laboratory, United States) and the WFPC2 Science Team.


For more information, please contact:
Lars Lindberg Christensen
Hubble European Space Agency Information Centre, Garching, Germany
Tel: +49-89-3200-6306 (089 within Germany)
Cellular (24 hr): +49-173-3872-621 (0173 within Germany)
E-mail: lars@eso.org