New Discovery: Cas A Supernova Explosion–Seeding the Universe with Building Blocks of Life

Casa1Heavy elements may be no more than rare cosmic pollutants, but they are exceedingly important to us. Without them, solid, rocky planets would be impossible, and the prospects for Earth-like life would be correspondingly dim.

The iron Chandra X Ray Space Telescope has recently imaged in Cas A might one day flow as hemoglobin in the blood of some future alien species. Fast moving knots of silicon from the Cas A supernova could provide the raw material for sand on otherworldly shores, where crashing waves of H2O send thunderous sound waves through a nitrogen-rich atmosphere.

A team of astronomers led by Dr. John Hughes of Rutgers University used observations from NASA's orbital Chandra X-ray Observatory to make an important new discovery that sheds light on how silicon, iron, and other elements were produced in supernova explosions. An X-ray image of Cassiopeia A (Cas A), the remnant of an exploded star, reveals gaseous clumps of silicon, sulfur, and iron expelled from deep in the interior of the star.

Chandra carries an instrument called the Advanced CCD Imaging Spectrometer (ACIS) that can measure the energy of incoming x-ray photons and associate them with specific chemical elements. Using the ACIS, astronomers are taking pictures of Cas A that reveal the distribution of heavy atoms like oxygen, silicon and iron in the supernova's rapidly expanding shell and that show how those elements are mixing into the ambient interstellar medium of gas and dust.
Just last month NASA released new ACIS images of Cas A at x-ray wavelengths emitted by ions of silicon (Si), calcium (Ca), and iron (Fe). On the eastern side of the supernova's shell, Ca and Si images reveal a high speed jet erupting into a relatively low-density region of the interstellar medium.

Scientists speculate that the jet might signify an asymmetry in the original supernova explosion. On the opposite side, observations at radio and other wavelengths indicate that Cas A is plowing into an interstellar molecular gas cloud that confines the shell's outward flow.

Above: Chandra X-ray Images of the Cas A supernova remnant. The silicon image shows a bright, broad jet breaking out of the upper left side of the remnant, and faint streamers in an opposite direction. The calcium image is similar to the silicon image, but less bright and clumpier. The iron image is different from the others. Since iron is the heaviest element shown, these maps support the suggestion that the layers of the star were overturned either before or during the explosion.

There are intriguing differences between the maps of Ca and Si and the map of Fe, which is clumpier and does not show the jet so clearly. Material rich in iron comes from the inner core of the star where fusion temperatures were highest. Scientists have examined these maps carefully and note that iron-containing knots from deepest in the star seem to be nearest the outer edge of the remnant. This means they were flung the furthest by the explosion that created Cas A. [more information]

Cas A's outer envelope is expanding at 800 km/s (about 1.73 million mph). That's rapid enough that images taken by Chandra over the years will show how knots in the shell change and cool. By monitoring these changes, Chandra scientists hope to learn more about how quickly and in what form different elements are deposited into the interstellar medium.

Even after more than 10 billion years of star formation, hydrogen and helium still are overwhelmingly the dominant atoms in the cosmos. Heavier atoms like the ones we see in the shell of Cas A are over represented on Earth because H and He are volatile gases that solar heating drives from the low-gravity terrestrial planets. Massive Jupiter, on the other hand, is made up almost entirely of hydrogen, as is the Sun.


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