Tuesday, November 23, 2010

Physicists Mimic Supernovae Formation in the Lab

A trio of physicists from the University of Toronto and Rutgers University have created a laboratory analogue for the type of supernova formed by the explosion of a white dwarf star.

Supernovae can form after the deaths of both giant stars many times the mass of our Sun or from smaller stars called white dwarfs. A white dwarf is a dense star at the end of its life cycle. It heats up over time until, at some point, it reaches a critical temperature that triggers an explosion, called a supernova. (Many, but not all, white dwarfs are thought to form supernovae.)

The initial explosion - called a flame front - starts within the star and balloons out, ejecting matter away from the star's core in a mushroom cloud shape. The highly energetic and super-bright matter wraps around the star and a supernova is born, as demonstrated in this University of Chicago video.

Already-formed supernovae are discovered by the dozens each year, but astronomers rarely observe the initial explosions, having the opportunity to do so only about twice a century.

Now, a group of physicists have created a sort of flame front analogue resembling a lava lamp in their laboratory. The physicists filled a cylindrical container with water and glycerol - a sweet-tasting liquid that sometimes makes its way into low-fat cookies and can be used to thicken up liqueurs (or in this case, water).

They then injected a water-based solution through a small tube at the bottom of the container. The solution reacts with the water-glycerol environment and becomes more buoyant, accelerating slowly to the top of the container.

In their experiment, the physicists observed that with the right water-glycerol mixture, the solution would create the same mushroom cloud shape, producing what they called a "vortex ring" at the top. The vortex ring would eventually detach from the plume of the
injected solution. Then the plume, undergoing a self-sustaining reaction with the water-glycerol mix, would form another vortex ring that would also detach. The process could be repeated several times before the plume reached the top of the container.

The spawning of the doughnut-shaped vortex ring resembles the mushroom cloud ejection of matter during the birth of a supernova. The scientists also found that if they lengthened their container, more vortex rings could form before reaching the top of the container, meaning that the reaction could potentially sustain itself indefinitely.

The high-tech lava lamp could give astronomers and physicists the opportunity to study the genesis of supernovae formation in the laboratory without having to wait 50 years for one to happen out in space.

The physicists' paper is due to appear in the American Physical Society's Physics Review E journal.

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