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A Star Set to Blow

2 October 2011 2 Comments
Fried Egg Nebula
The Fried Egg Nebula, or IRAS 17163-3907

IRAS 17163-3907 is a star that is about 13,000 light years from us.  Although its mass is about 20 times that of the Sun,  it is quite a faint star in the heart of the Milky Way.  Nothing remarkable there then.  But this picture is as the star is observed using the visible wavelengths it gives off. If you look in the infra-red spectrum, specifically with a wavelength of 12 x 10-6m,  you will see IRAS 17163-3907 in a whole new light.

A team of scientists, including some from the University of Manchester, have done just that and found that IRAS 17163-3907 (known as the Fried Egg Nebula) is really quite a remarkable object.  When you look in the infra-red region this is one of the 30 brightest stars in the sky; it is 500,000 times brighter than the Sun.  It is also at a fascinating stage of its life because it is blowing away its outer layers in preparation for the Universe’s biggest explosion, a supernova. The star in the middle of all this has just been classified as a yellow hypergiant and this makes IRAS 17163-3907 very rare indeed.

The new picture shows two shells of cloud that surround the star.  The clouds are a mixture of dust, made of compounds of silicon and oxygen (silicates), and gas.  If IRAS 17163-3907 was in our solar system the star itself would extend all the way out to the orbit of Jupiter. The Earth would be sunk deep inside the star and the surrounding nebula would extend beyond the orbit of Neptune.

Stars don’t stay as yellow hypergiants for long in the life-time of the star.  Stars start life as huge balls of hydrogen.  The gravitational pressure is so great that the hydrogen atoms crush together and get hotter and hotter.  In this maelstrom atoms are slammed into each other so hard that they stick together and form larger atoms releasing energy in the process.  This would be helium in this case and causes an outward pressure working against gravity, and this is the stage that our Sun is at right now. When a star runs out of fuel this seething cauldron of nuclear fusion collapses due to the pull of gravity; think of deflating a bouncy castle.  This collapse causes sufficient heat to be generated to start fusing together larger atoms, and will continue until all the helium has run out.  This process continues making larger and larger atoms up to iron.


The future for IRAS 17163-3907 is bright though. What happens next is that as the star runs out of nuclear material it collapses again. But this time the pressures are so great that the atoms themselves collapse. When further collapse is no longer possible there is a shock wave that rebounds outwards and this is the supernova.

So what the researchers have found is a that this star is just entering the final phase before blowing itself apart. They are amazed that it has gone unnoticed for so long but what a find it is! Scientists believe that this will be one of the next supernovae in our galaxy. This is the closest yellow hypergiant seen so far and so we have a ring-side seat for one of the biggest shows in the Universe.

See the original article at Astronomers crack the Fried Egg Nebula