# Ice smothers dying star



## Brian G Turner (May 1, 2004)

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.  

 Most planetary nebulae are distinctive, but few are as extreme as NGC  6302, also known as the Bug Nebula. The fiery, dying star at its centre  is shrouded by a blanket of icy hailstones.

 The following image of the Bug Nebula, taken with the NASA/ESA Hubble Space  Telescope, shows impressive walls of compressed gas, laced with  trailing strands and bubbling outflows. A dark, dusty torus surrounds  the inner nebula (seen at the upper right). At the heart of the turmoil  is one of the hottest stars known. Despite a sizzling temperature of at  least 250,000 degrees C, the star itself has never been seen, as it is  hidden by the blanket of dust and shines most brightly in the  ultraviolet, 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. 

 Albert Zijlstra from UMIST in Manchester, UK, who leads a team of  astronomers probing the secrets of this extreme object, says: "What  caught our interest in NGC 6302 was the mixture of minerals and  crystalline ice - hailstones frozen onto small dust grains. Very few  objects have such a mixed composition." 

 The dense dark dust torus around the central star contains the bulk of  the measured dust mass and is something of an enigma to astronomers.  They believe the nebula was expelled around 10,000 years ago, but do  not quite understand how it formed and how long the dust torus can  survive evaporation by the now very hot central star.  

 From: http://spaceflightnow.com/news/n0404/30fireandice/


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