According to a new report from the Lawrence Livermore National Laboratory, an international team of scientists has solved the mystery of how stars explode in supernovae. The report appears in the February 20 issue of the journal Nature.
By means of NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR), a high-energy X-ray observatory, the international partnership produced the first-ever map of radioactive material in a supernova vestige, named Cassiopeia A. The findings expose how shock waves probably tear apart and eventually kill enormous dying stars.
A supernova is the catastrophic death of a star, which is tremendously radiant and causes a burst of radiation that habitually – albeit briefly – outshines an entire galaxy before vanishing from view. The explosion expels most or all of a star’s substance at a velocity of 10 percent of the speed of light, driving a shock wave into the adjoining interstellar medium.
“Stars are spherical balls of gas, and so you might think that when they end their lives and explode, that explosion would look like a uniform ball expanding out with great power,” said Fiona Harrison, the principal investigator of NuSTAR at the California Institute of Technology and one of the lead authors of a new paper. “Our new results show how the explosion’s heart, or engine, is distorted, possibly because the inner regions literally slosh around before detonating.”
The Cassiopeia A vestige was created when a massive star blew up as a supernova over 11,000 years ago, leaving a dense stellar corpse and its ejected remains. Since the supernova was so far from Earth, the light only reached our planet some 350 years ago, when it may have appeared to be a new, brilliant star.
“[Cassiopeia A] was a mystery for so long but now with the map of radioactive material, we’re getting a more complete picture of the core of the explosion,” said Bill Craig, an LLNL scientist now at UC Berkeley and coauthor of the paper.
The newest findings suggest the exploding star moved about erratically, reenergizing the stalled shock wave and permitting the star to discharge its outer layers.
According to NASA’s NuSTAR project website, “The NuSTAR instrument consists of two co-aligned grazing incidence telescopes with specially coated optics and newly developed detectors that extend sensitivity to higher energies as compared to previous missions such as Chandra and XMM. After launching into orbit on a small rocket, the NuSTAR telescope extends to achieve a 10-meter focal length. The observatory will provide a combination of sensitivity, spatial, and spectral resolution factors of 10 to 100 improved over previous missions that have operated at these X-ray energies.”