For the first time, astronomers led by a team at UC Berkeley have peered into the heart of an exploding star, giving them unprecedented insight into the fundamental physics behind how stars crescendo into supernova explosions.
In June 2012, a high-energy X-ray telescope funded by NASA called Nuclear Spectroscopic Telescope Array, or NuSTAR, was launched to map Cassiopeia A, or Cas A, the supernova remnant of a star that exploded in 1671 about 11,000 light years away from Earth. Using NuSTAR, astronomers were able to map the decay of core elements produced by the supernova explosion — a “holy grail” observation for the field of astrophysics.
For the past 343 years since the supernova exploded, its products — such as iron and titanium-44 — have been expanding outwards, giving astronomers a front-row seat to study the innermost elements of the supernova. With the results, researchers can better understand the nuclear processes that perpetuated the entire explosion.
“Cas A is very special in that sense — it’s had enough time to expand, so we can get a nice image of the distribution of the titanium,” said Steven Boggs, UC Berkeley professor of astrophysics and co-author of the paper published last month in Nature.
The UC Berkeley NuSTAR team, led by Boggs, helped build the instruments for the mission, whose operations are run entirely out of the Space Sciences Laboratory. The mission is also carried out by researchers from Caltech, Columbia University, Goddard Base Flight Center and the Jet Propulsion Laboratory.
The astronomy community agrees that when a massive star explodes, it forms a core that collapses at the exterior and rebounds outward, but opinions are varied on the mechanics that propel this explosion. The latest findings support a “sloshing around” hypothesis in which stars disperse radioactive material disproportionately, energizing a blast wave that sets off detonation.
“This titanium material shows a distribution that indicates the explosion was not spherically symmetrical — in other words, it was sort of blob-y. It shot out in other directions more than others,” said Alex Filippenko, a campus astronomy professor. “From the previous observations, it wasn’t clear what’s going on, but with this titanium material from the guts of the exploding star, you can see clearly this asymmetry.”
Although the pressures, temperatures and densities that govern the cosmos are not comparable to those on Earth, the elements at play are the same and were primarily formed through the production of stars and in supernova explosions. Thus, the study of these phenomena can provide insight into the nature of the universe at large, Boggs explained.
“There’s a series of nuclear reactions, and those nuclear reactions are producing the heavier elements we see in the universe around us,” Boggs said. “So we, of course, want to understand that process to better understand how the universe is evolving.”