|237 Feb 20, 2014||NuSTAR creates the first map of 44Ti emission in Cassiopeia A|
The NASA's high-energy X-ray observatory Nuclear Spectroscopic Telescope Array (NuSTAR) has created the first map of radioactive element in the Cassiopeia A (Cas A) supernova remnant. The radioactive element is titanium-44, which has an unstable nucleus produced at the heart of the exploding star.
The NuSTAR map of Cas A shows the titanium concentrated in clumps at the remnant's center, strongly suggesting that the exploding star literally sloshed around, re-energizing the stalled shock wave and allowing the star to finally blast off its outer layers. These results have been published in the February 20 issue of Nature.
"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 (Caltech) in Pasadena. "Our new results show how the explosion's heart, or engine, is distorted, possibly because the inner regions literally slosh around before detonating."
The NuSTAR titanium-44 map also casts doubt on other models of supernova explosions, in which the star is rapidly rotating just before it dies and launches narrow streams of gas that drive the stellar blast. Though imprints of jets have been seen before around Cas A, it was not known if they were triggering the explosion. NuSTAR did not see the titanium, essentially the radioactive ash from the explosion, in narrow regions matching the jets, so the jets were not the explosive trigger.
"With NuSTAR we have a new forensic tool to investigate the explosion," said the paper's lead author, Brian Grefenstette of Caltech. "Previously, it was hard to interpret what was going on in Cas A because the material that we could see only glows in X-rays when it's heated up. Now that we can see the radioactive material, which glows in X-rays no matter what, we are getting a more complete picture of what was going on at the core of the explosion."
The Italian participation to NuSTAR includes the provision of the Malindi ground station (ASI), the ASI Science Data Center (ASDC), which contributes to the development of the NuSTARDAS software package and will host an official mirror of the NuSTAR scientific data archive, and a team of scientists of the Istituto Nazionale di Astrofisica (INAF) to collaborate on the primary scientific mission goals.
The NuSTAR team at ASDC is composed by M. Perri (INAF archive scientist), S. Puccetti (INAF archive scientist) and P. Giommi (ASDC Responsible).
For more details on NuSTAR, see:
NuSTAR image of the Cas A supernova remnant superimposed with the NASA's Chandra orbiting telescope image. Blue shows NuSTAR's map of the distribution of titanium-44 produced in the core of the explosion 340 years ago, while red and green are X-ray emissions detected by Chandra of heated iron and silicon/magnesium, respectively.
Image credit: NASA/JPL-Caltech/CXC/SAO.