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Toxic Compound In Space Signals Starbirth
Paris ESA Oct 10, 2001 Centuries ago it was commonly believed that comets carried disease in their tails. Nowadays we know the only 'disease' you can get from a comet is a cold -- if you stay out too long at night watching it! But these old beliefs were not completely wrong: comet tails do contain an extremely poisonous chemical compound -- hydrogen cyanide. Now a team of Dutch and German astronomers using ESA's Infrared Space Observatory and the James Clerk Maxwell Telescope on Hawaii have discovered that this poison can help them to understand the birth of massive stars -- its presence is a sign that a massive baby star has begun to warm up. Annemieke Boonman (Leiden University) and Ronald Stark (Max-Planck-Institut f�r Radioastronomie, Bonn) studied a massive protostar (a star in the very early stages of development) called GL 2591, located 3000 light-years away. GL 2591 is embedded in a cloud of dust and gas a thousand times larger than our entire Solar System, and it is spewing out powerful jets of hot gas at hundreds of kilometres per second. The team detected hydrogen cyanide deep in the interior of this cloud, and realised that this meant that the massive baby star was already hot at its core. As Boonman explains, "Detecting large amounts of hydrogen cyanide toward the centre of a massive protostar means that it has already started to warm up. From this information we can determine the degree of evolution, and therefore the age, of the star." Astronomers now know that GL 2591 is between a few tens of thousands and a hundred thousand years old, which means that in a few hundred thousand years more its birth process will be over and a new star, ten times more massive than our Sun will be shining in the sky. Will anyone be there to see it?
A cold cocoon warming up In the case of massive stars, those with at least ten times as much mass as the Sun, scientists know even less since most of the regions in space where massive stars are formed happen to be farther away from Earth than low-mass star-forming clouds. As a result, there is a long list of pending questions regarding how massive stars form. For instance, when does the star-to-be begin to get 'warm'? The cloud of dust and gas is initially very cold, at about minus 250 degrees Celsius, and obviously it gets warmer as the star-forming process proceeds. In principle, astronomers can trace the increase in temperature by studying the chemical composition of the cloud. As soon as the core of the massive embryo-star reaches room temperature the chemistry in the cloud changes: the existing molecules start to combine, and more complex compounds are formed. So the presence of complex molecules in the cloud tells astronomers that the baby star has begun to warm up. But there is a technical problem: current instrumentation only permits the detection of complex molecules in the cloud when there are plenty of them, that is, when the chemical changes are well advanced. If astronomers want to mark the true birth of the star's hot core, then they have to identify a molecule that not only needs warm temperature for its synthesis, but that is also much easier to detect than the complex molecules used so far as indicators. The Dutch-German team found that the toxic hydrogen cyanide molecule fits the bill.
A revolution in astro-chemistry
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