NuSTAR gives tantalizing hints about how stars go supernova
By Anthony Wood
February 21, 2014
NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) is unraveling the mystery of how stars go supernova by mapping the remnants of radioactive material left in the wake of a supernova. The findings go against previous theories to create a more chaotic view of the conditions prevailing directly before a star explodes.
NuSTAR, launched on 13 June, 2012, represents the first telescope capable of imaging radioactive elements left behind after a supernova. This is achieved by focussing its search to the high energy X-ray (6 -79 KeV) area of the electromagnetic spectrum. Previous telescopes, which hosted coded apertures, were found to be insufficient in observing light in this part of the electromagnetic spectrum.
The array gathered the new data by observing the remnants of a supernova designated Cassiopeia A, a star which before it went supernova was roughly eight times as large as our Sun. When mapping Cas A the telescope searched for titanium-44, a radioactive isotope which can only be forged in the final stages of a dying star, and therefore the perfect element with which to detect and map a supernova explosion.
"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," said Brian Grefenstette of Caltech. "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."
NuSTAR found that the titanium-44 was primarily found grouped around the center of Cas A. This has led NASA scientists to deduce a possible explanation for the death of these stellar giants.
It appears that the cause of a supernova is a massive shock wave that literally tears the star apart. Sometimes, however, the shock wave fails to reach a critical mass and stalls, preventing the star from shedding its outer layers and effectively preventing the supernova from taking place.
Information gathered from NuSTAR's observation of Cas A suggests that an exploding star sloshes around like a disturbed liquid, with the effect of kick-starting the stalled shock wave, continuing the supernova.
This chaotic new theory shakes off previous symmetrical theories regarding the processes required to create a supernova put forward by running data through powerful supercomputers, the results of which suggested an explosion which was symmetrical in all directions.
The ability to detect elements such as titanium-44 has also cast a level of doubt on some previous models of supernova explosions. One such model involved the dying star spinning at a great speed prior to exploding, however while searching the tell-tale jets ejected by the star during the high velocity spin, NuSTAR detected no signatures of titanium-44, meaning that the jets emitted from the star were not the trigger of the supernova explosion.
The team continues to examine Cas A in an attempt to further understand the dramatic ends of these stellar behemoths. A paper on the findings was recently published in Nature.
The video below shows a sloshing star going supernova.