Some primordial stars between 5,000 and 56,000 times the mass of the sun may have died unusual deaths in which they exploded as a supernova without leaving behind black holes.
Researchers from the University of California, Santa Cruz (UCSC) and the University of Minnesota ran supercomputer simulations at the Department of Energy's (DOE's) National Energy Research Scientific Computing Center (NERSC) and Minnesota Supercomputing Institute at the University of Minnesota to make their findings. They also employed CASTRO - a multidimensional compressible astrophysics code developed at Berkeley Lab by scientists Ann Almgren and John Bell.
These first-generation stars are believed to have produced the first heavy elements, sending these substances far into space when they died. The researchers hope by looking at the behavior of these early stars we can gain insight into how the universe developed into what it is today.
"We found that there is a narrow window where supermassive stars could explode completely instead of becoming a supermassive black hole - no one has ever found this mechanism before," said Ke-Jung Chen, a postdoctoral researcher at UCSC and lead author of the Astrophysical Journal paper. "Without NERSC resources, it would have taken us a lot longer to reach this result. From a user perspective, the facility is run very efficiently and it is an extremely convenient place to do science."
The research team used a one-dimensional stellar evolution code called KEPLER, which factors in stellar processes such as nuclear burning and convection. Through this method the team found the stars in question lived for 1.69 million years before becoming unstable due to relativistic effects. Once the star starts collapsing, elements such as "oxygen, neon, magnesium silicon," and helium are synthesized. When these stars explode they could enrich entire galaxies with these crucial elements.
"My work involves studying the supernovae of very massive stars with new physical processes beyond hydrodynamics, so I've collaborated with Ann Almgren to adapt CASTRO for many different projects over the years," says Chen. "Before I run my simulations, I typically think about the physics I need to solve a particular problem. I then work with Ann to develop some code and incorporate it into CASTRO. It is a very efficient system."
