Surprisingly, this “one-dimensional” simulation produced the correct brightness curve. “There was no way I would have seen that coming,” Bildsten marveled. “They’re showing they can drop a supernova on Phillips’ relationship, so that’s pretty exciting.”
To verify that a detonation can occur in the first place, however, two other groups were busy developing sophisticated supercomputer simulations of the D6 scenario in three dimensions.
One of these teams recently show that the D6 scenario can actually trigger a supernova. The researchers, led by Ruediger Pakmor at the Max Planck Institute for Astrophysics in Garching, Germany, simulated a primary white dwarf with a thick outer layer of helium. As the star sucked even more helium from its companion, its outer layer ignited. The explosion quickly spread around the white dwarf, sending a shock wave deep inside the core that blasted carbon and oxygen away.
But Pakmor’s simulations also produced a strange result. The shock wave passing through the primary white dwarf sometimes hit the companion dwarf hard enough to trigger a supernova in that star as well. This happened in the simulations when the mass of the companion was less than 70% of the mass of our sun, as is usually the case with white dwarfs.
If the two white dwarfs often go to supernova together, this could explain why we see fewer hypervelocity white dwarfs. But astronomers have cautiously greeted the news of Pakmor’s double supernova simulations. “I’m not convinced that’s happening,” Shen said, “but it’s a really interesting possibility.”
Another team, led by Robert Fisher at the University of Massachusetts, Dartmouth, used a thinner helium layer than Pakmor. In their simulations, they saw the helium ignition move more slowly around the dwarf, and the resulting shock wave converged to a point off-center from the carbon-oxygen core. The kernel then failed to explode in a type Ia supernova.
Both groups are baffled by the conflicting results. Pakmor’s team tried a thinner helium layer like Fisher’s, but still found that their system had gone supernova.
A challenge for these simulations is that the helium thickness and other conditions are only guesses. Another problem is that, to simulate star-sized objects, the simulations roughly divide space into kilometer-sized chunks. But the concentration of heat that triggers a detonation occurs on the centimeter scale. Scientists make choices about how to capture the interplay between these disparate scales.
For now, the book remains open on the origins of Type Ia supernovae. Until the discrepancies can be resolved, both teams are reluctant to conclude that the D6 scenario is responsible for all or even most of them. Still, finally seeing one explode in a supercomputer was a big step forward, even if seeing two was a surprise.
Original story reproduced with permission from Quanta Magazine, an editorially independent publication Simons Foundation whose mission is to enhance the public understanding of science by covering developments and trends in research in mathematics and the physical and life sciences.
