U of T Physicists Unleash "Supernova in a Jar"




U of T Physicists Unleash “Supernova in a Jar”

It’s not hard to notice a supernova, the massively violent cosmic explosion signaling the death of a star. In the span of a few short weeks, this cosmic flashbulb can shine brighter than entire galaxies. The sheer force of the explosion—think on the order of a million-billion-trillion megatons of TNT—provides enough energy to fuse atomic nuclei into the heavier elements that make life possible.
While the products of a supernova (like oxygen, carbon, and iron) can easily be detected through astronomical observation and analysis, peeking inside at the reactants that trigger these detonations is much trickier.
A team of physicists at the University of Toronto and Rutgers University tried to do just that recently—they simulated the intrastellar processes believed to give rise to some supernova.

Their research, led by U of T doctoral candidate Michael Rogers, will appear in the December edition of Physics Review E.
Dubbed the “supernova in a jar” experiment, the study gives scientists a first glimpse into the complex fluid dynamics at play inside a dying star, seconds before it blows up.
To misappropriate the words of General Douglas MacArthur, “old stars never die, they just fade away.” This is the case for the majority of stars in our universe, which, after burning through their fuel, collapse inward to form a dim, dense ball known as a white dwarf. In most cases, white dwarves simply radiate out what’s left of their heat and go dark. More rarely, however, these earth-sized concentrations of plasma will suck up matter from a nearby star. Like so many clowns in a Yugo, the dwarf’s own mass will gradually increase, until it reaches a threshold where it can no longer hold together.

20100612supernovainajar.jpgThe Crab Nebula formed in the wake of a supernova observed by medieval Chinese and Arab astronomers in 1054 A.D. Photo by J. Hester and A. Loll from the NASA Goddard Photo and Video Flickr Pool.

Then something weird happens. From the depths of the star’s interior, a “plume” of blazing carbon and oxygen bubbles rapidly towards the surface.
For fluid physicists like Rogers, a plume is a stream of buoyant material supplied from a single source (think smokestacks and volcanoes). Like the smoke rings you and your moustache-twirling friends blow at the faculty club whilst sipping scotch and commenting on world affairs, the top of a plume typically swirls out into a mushroom-shaped head.
For Rogers’ team, it’s the action of these “plume heads” that is most interesting. Their simulation shows that these billowing rings can actually ignite a chain reaction that drives and accelerates their progress upwards. Replace the simple heads of Rogers’ experiment with an explosive carbon and oxygen “flame head,” and you’ve got what supervising professor Stephen Morris calls “a nuclear-fueled smoke ring.”
In a white dwarf, the vortices created by these self-propelled flame heads suck in and mix up the surrounding reactants, setting off a massive fusion reaction that, in seconds, spirals into a full-blown supernova. “Kind of like lighting a fuse and letting the whole thing blow,” Morris adds.
The professor also urges you to watch this striking University of Chicago computer visualization of the process, which physicists call the deflagration to detonation transition:

Oddly enough, Rogers and his colleagues had no idea they would be studying supernovae when they first embarked on this project. It was only after astrophysicist Natalia Vladimirova drew the analogy in her own work that the team of fluid physicists came to appreciate the full scope of their model.
Call it blind luck, or a fortuitous meeting of the minds. You could also just call it science. The “supernova in a jar” study illustrates the unplanned, undirected chanciness that guides so much scientific discovery.
“A supernova is a dramatic example of this kind of self-sustaining explosion in which gravity and buoyancy forces are important effects,” Rogers notes in a U of T press release. But, both Rogers and Morris stress to Torontoist, it’s only one example.
For Rogers, who’s built his doctoral thesis out of this project, what’s most interesting are the fluid dynamics themselves. “We had no idea…that it was so complicated,” he says.
Why are there multiple plume heads? Why do the heads detach from the conduit? Why do they accelerate upwards? There are enough questions here to keep a budding hydrodynamicist busy for quite some time. After all, a supernova lasts for mere weeks, while a PhD can take years.