Tragedy 4 000 light years away

Astronomers are hailing the photograph of a dust-cloaked star as one of the most dramatic pictures ever taken. The image from the Hubble Space Telescope shows the dying star 4,000 light years away being bombarded by hailstones.

However, scientists are baffled by the vast butterflylike "wings" around the star.

These are dust clouds produced as the star dies. But scientists cannot work out how the so-called Butterfly Nebula formed its distinctive shape, as the star at its heart is actually round. Lars Christensen of the European Space Agency, which operates the Hubble Space Telescope jointly with Nasa, said: "It's a big mystery to us all - how a round star like our own sun can create this effect, which is so symmetrical. It's amazing."

The image reveals huge walls of compressed gas and bubbling outflows. A massive ring of dark dust hiding the star also has experts baffled, reports

According to the Bug Nebula, NGC 6302, is one of the brightest and most extreme planetary nebulae known. At its centre lies a superhot dying star smothered in a blanket of ‘hailstones’. A new Hubble image reveals fresh detail in the wings of this ‘cosmic butterfly’.

This image of the Bug Nebula, taken with the NASA/ESA Hubble Space Telescope (HST), shows impressive walls of compressed gas. A torus (‘doughnut’) shaped mass of dust surrounds the inner nebula (seen at the upper right).

At the heart of the turmoil is one of the hottest stars known. Despite an extremely high temperature of at least 250 000 degrees Celsius, the star itself has never been seen, as it shines most brightly in the ultraviolet and is hidden by the blanket of dust, making it hard to observe.

Chemically, the composition of the Bug Nebula also makes it one of the more interesting objects known. Earlier observations with the European Space Agency’s Infrared Space Observatory (ISO) have shown that the dusty torus contains hydrocarbons, carbonates such as calcite, as well as water ice and iron. The presence of carbonates is interesting. In the Solar System, their presence is taken as evidence for liquid water in the past, because carbonates form when carbon dioxide dissolves in liquid water and forms sediments. But its detection in nebulae such as the Bug Nebula, where no liquid water has existed, shows that other formation processes cannot be excluded.

But what excites astronomers most is not the shimmer of the wings but a dark band that bisects them. A dense ring of gas and dust - called a torus - girdles and obscures the dying star and contains most of the star's ejected gas.

"We really don't know what causes the material to be ejected primarily in one plane," says Albert Zijlstra, an astronomer at the University of Manchester Institute of Science and Technology, UK. His analysis of the Hubble image and others will appear in Astronomy & Astrophysics.

The Bug Nebula is one of about 1600 known planetary nebula. These form when stars up to eight times the mass of the Sun begin to die. They bloat into red giants before shedding as much as half their mass as gas and dust nebulae, which often take on the pinched appearance of the Bug Nebula, inform

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