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BookmarkScienceDaily (Dec. 22, 1999) — NEW BRUNSWICK/PISCATAWAY, N.J. -- A team of astronomers led by Rutgers Professor John P. Hughes has made an important new discovery using NASA's orbital Chandra X-ray Observatory. They have detected key evidence that sheds light on how silicon, iron and other elements were produced in massive supernova explosions. For the first time, scientists have clearly identified what was produced and where deep within an exploding star.
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The team's findings appear online in the Astrophysical Journal Letters at <http://www.journals.uchicago.edu/ApJ/journal/rapid.html>, and are slated for print publication Jan. 10, 2000. Hughes, Rutgers graduate student Cara Rakowski, David Burrows of Pennsylvania State University and Patrick Slane of the Harvard-Smithsonian Center for Astrophysics are authors of the paper "Nucleosynthesis and Mixing in Cassiopeia A."
The Chandra X-ray Observatory is NASA's newest space telescope and is the world's most powerful X-ray telescope. Chandra has eight times greater resolution and can detect sources more than twenty times fainter than any previous X-ray telescope. Chandra was launched by the Space Shuttle Columbia on July 23, 1999 with an orbit 200 times higher than the Hubble Space Telescope. It detects images from X-ray sources that are billions of light years away.
According to Hughes, one of the most profound conclusions of 20th century astronomy is that nearly all elements other than hydrogen and helium were created in the interior of stars. "During their lives, stars are factories that take the simplest element, hydrogen, and convert it into heavier ones," he said. "After consuming all the hydrogen in its core, a star begins to collapse and its central parts form a black hole while the rest of the star is blown apart in a tremendous supernova explosion."
Supernovae are rare, occurring only once every 50 years or so in a galaxy like our own. Hughes and his collaborators used Chandra to study the exploded remains of a 300-year old supernova called Cas A, in the area of the constellation Cassiopeia, learning more about the genesis of these elements.
"When I first looked at the Chandra image of Cas A, I was amazed by the clarity and definition," said Hughes. "The image was much sharper than any previous one and I could immediately see lots of new details."
In addition to the image clarity, the Chandra data held great potential for measuring the composition of stellar material concentrations visible in Cas A. Not only could the astronomers determine the composition of these many knots and filaments, but they could also infer where in the exploding star these features had originated.
For example, the most compact and brightest knots were composed mostly of silicon and sulfur, lighter elements with little or no iron. This pointed to an origin deep within the star's interior, where the temperatures had reached 3 billion degrees during the collapse and resulting supernova explosion. Elsewhere, they found fainter features that contained significant amounts of iron, a heavier element, along with some silicon and sulfur. This material was produced even deeper within the star, where the temperatures during the explosion had reached higher values of 4 billion to 5 billion degrees.
The astronomy team also discovered that the iron-rich features from deepest within the star were closest to the edge of the supernova remnant. This meant that they had been flung the farthest by the explosion that created Cas A. Even now this material appears to be streaming away from the site of the explosion with greater speed than the rest of the remnant.
By studying the Cas A Chandra data further, astronomers hope to identify which of the processes that have been proposed by theoretical studies is likely to explain supernova explosions, both in terms of the explosion dynamics and elements produced.
"In addition to understanding how iron and the other elements are produced in stars, we also want to learn how they get out of stars and into the interstellar medium. This is why the study of supernovae and supernova remnants is so important," said Hughes. "Once released from stars, newly created elements can then participate in the formation of new stars and planets in a great cycle that has gone on numerous times already. It is remarkable to realize that our planet Earth, and indeed even humanity itself, is part of this vast cosmic cycle.
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EDITOR'S NOTE: For more information, contact John P. Hughes who is currently on-leave in France but can be reached by telephone: 33-1-69-08-43-84 or e-mail at jph@physics.rutgers.edu. For specific information on Chandra and to access high-resolution digital versions of the X-ray images, visit http://chandra.harvard.edu, http://chandra.harvard.edu/photo/casajph/ and http://chandra.nasa.gov.
An online version of the newsrelease, with links to images, can be found on NASA's Marshall Space Flight Center Web site at http://www1.msfc.nasa.gov/NEWSROOM/news/releases/1999/99-302.html.
