NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) has produced the first map of radioactive material in a supernova remnant. Surface Optics Corporation used advanced ion-assisted deposition technology to apply an X-ray transparent, solar-rejecting thermal control coating to the covers protecting NuSTAR’s optics modules.
NuSTAR’s observations of the youngest supernova remnant in the Milky Way, Cassiopeia A (Cas A, for short), reveal new information about the fantastic collapse and explosions of massive stars.
“Hot bubbles at the center of the core blast out through the shockwave ripping the star apart, this leaves behind a pattern of radioactive ash that NuSTAR can observe hundreds of years later,” explained Brian Grefenstette of Caltech.
Grefenstette is the lead author of a paper about spatial maps and spectral properties of the Cas A titanium-44 published in the Feb. 20 issue of Nature.
In the above image, radioactive material Titanium-44 detected by NuSTAR at energies ranging between 68 – 78 kiloelectron volts (keV) is shown in blue. Lower-energy X-rays from non-radioactive material, data collected previously at energies 1 to 7 keV with NASA’s Chandra X-ray Observatory, are shown in green, red, and yellow.
NuSTAR 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
While other telescopes have detected this radioactivity in Cas A before, NuSTAR is the first capable of pinpointing and mapping the location of the radioactivity. The positioning of titanium-44, a direct tracer of the supernova blast, provides important evidence on how stars explode.
“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 fact that the titanium is concentrated in clumps at the core supports a theory referred to as “mild asymmetries.” In this scenario, material sloshes about at the heart of the supernova, reinvigorating the shock wave and allowing it to blow out the star’s outer layers.
“This is why we built NuSTAR,” said Paul Hertz, director of NASA’s astrophysics division in Washington. “To discover things we never knew – and did not expect – about the high-energy universe.”
NuSTAR is a Small Explorer mission led by Caltech in Pasadena and managed by NASA’s Jet Propulsion Laboratory.
For more information on the NuSTAR mission, visit: www.nustar.caltech.edu/