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Cauldron in Cassiopeia: New Chemistry Revealed
By Maia Weinstock
Staff Writer
posted: 07:00 am ET
21 September 2000
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tycho_nova_xmm_000920 In 1572, the Danish astronomer Tycho Brahe was witness to one of the most exciting cosmic phenomena known to exist -- a supernova, or gargantuan stellar explosion. Little did he know that this same supernova which now bears his name would be so well-studied in later years that astronomers would know such intricate details as its chemical composition. Today the still-brilliant remnant of the Tycho supernova, which is located in the constellation Cassiopeia, has two major observers the European XMM-Newton telescope and the NASA Chandra X-ray Observatory. These telescopes have, in a matter of months, already uncovered a wealth of data about the exploded star. Most recently, the European telescope has detailed the composition of Tycho, identifying in the supernova remnant many of the same chemical building blocks used to make the planets and life on Earth. Supernovae are some of the most violent events in the universe. They occur at the end of a giant stars life, when the star has used up all of its nuclear fuel. When that happens, the stellar core collapses in on itself, releasing huge amounts of energy into the local interstellar space around it in a giant explosion.
Tycho Brahe, the Danish astronomer after whom the Tycho supernova was named Tycho Brahe was witness to one of the only three or four supernovae known to explode during human history. Though today the Tycho supernova is visible only through a telescope, at the time of its initial blast it was visible to the naked eye for about 18 months. In fact, the initial explosion appeared as one of the brightest stars in the sky. Today, astronomers are not studying visible light from the supernova, as Tycho would have seen it, but rather its X-ray light, which can be detected by both XMM-Newton and Chandra. Scientists are interested in supernovae because they are thought to be great cosmological chefs. Most of the chemicals in the universe are created as a direct result of supernova explosions. "Theyre basically big cookers," said Richard Mushotsky, an XMM project scientist at NASAs Goddard Space Flight Center. "They cook the original elements like hydrogen and helium and they make them into all the stuff that we learned about in chemistry class carbon, nitrogen, iron, etc.""We astronomers are fond of saying that every atom we exist of once-upon-a-time lived in the center of a star that exploded like this," added Mushotsky. "So what both XMM and Chandra are able to do with exquisite accuracy is actually measure and map these elements." 
False-color elemental "map" of the Tycho supernova, based on raw data from the XMM-Newton space telescope XMM-Newton has actually been able to "see" and image such heavier elements with its sensitive instruments. Astronomers have also been able to determine the density of these elements and the temperatures of surrounding gases. According to researchers working with the scope, these temperatures can be up to millions of degrees super hot. "Its interesting to study supernova composition with XMM because what youre looking at is the original debris from the star," said Una Hwang, an astronomer at Goddard. "As a supernova remnant gets older and older, it heats up a lot of the surrounding material, which then has a very different composition. This supernova is still very young." Another thing astronomers are learning from observations of Tycho with XMM-Newton is that their ideas of how supernovae form may need a little revising. In particular, the most recent XMM images have shown that the supernova is not a perfect round ball, as researchers once believed all supernovae should be. "When this star exploded, it should have been a sphere. But when you look at these pictures, you see its not," said Mushotsky. "Our simple ideas about how supernovas explode are basically wrong. So now, we have to fix them with more research."
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