Two researchers from the American Museum of Natural History have built a new mathematical model that explains how white dwarfs, failed stars at the end of their lives, explode as a supernova in a last spectacular hurrah.
The model looked at a specific scenario that happens when two white dwarfs orbiting each other merge into a single object. Observations suggest that all these mergers result in a supernova regardless of their total mass, which doesn’t sit well with our understanding of physics.
Stars only go supernova when their mass goes beyond a certain limit, so something else must help trigger the explosion. The model suggests that the gravitational interaction between the two objects as they approach each other might play that role.
“Basically, we’ve proposed that if you have two white dwarfs spiraling towards each other and you shake one of them the right way for long enough, one will either blow up or you’ll bring the objects closer together faster for an eventual detonation,” co-author Barry McKernan said in a statement.
The stars enter a resonance phase, a special type of oscillation, where the energy of the system increases dramatically but the external forces driving the oscillation do not change. The researchers say that this is similar to how you can push a child on a swing with minimal effort.
“Pushing your kid in time with the natural interval, or frequency, of the swing ramps up the energy and gets them higher and higher,” McKernan said. “There’s a similar effect in our model, where a lock on the frequency produces a series of rapid jumps in energy that are deposited into the white dwarfs.”
The study, which is published in the Monthly Notices of the Royal Astronomical Society, suggests that the white dwarfs spiral towards each other, emitting gravitational waves, and during this process, they tug at each other until at least one of them reaches the right frequency.
This is not the only way for white dwarfs to explode. If white dwarfs have a normal star as a companion, they can sometimes steal material until they become heavy enough to initiate the supernova phase. All the white dwarf supernovae are classified as Type Ia. They all appear to have the same luminosity, a characteristic that is useful to estimate how far away they are.
“Type Ia supernovae are extremely important objects in physics, best known for their role in revealing that the expansion of the universe is accelerating,” said co-author Saavik Ford.
For this reason, astronomers want to make sure their origin is crystal clear, as it might turn out that they are not as similar as we think they are.