Physicists from the University of Toronto and Rutgers University studying the effects of mixing two reactive chemicals have discovered a new phenomena which mimics the explosion of a type of supernova in miniature. The observation centers around two reactants which create a self-sustaining vortex ring without any external forces or additional catalysts. These kinds of reactions are occurring around us all the time in the atmosphere and oceans as well as stars, but this effect has never been seen and this new ability to study it will help further our understanding of the evolution of the universe.
"We created a smaller version of this process by triggering a special chemical reaction in a closed container that generates similar plumes and vortex rings," says Stephen Morris, a physics professor at University of Toronto.
When two fluids of different chemical composition mix, there may be an instability. In a non-reactive fluid medium, a more buoyant fluid will create a plume as it rises through the less buoyant fluid. However, when two reactive fluids are passed through one another the results are less predictable as the reaction itself may stir the chemicals, catalyzing the reaction further and leading to a runaway process known as an "autocatalytic" reaction.
The iodate-arsenous acid system is one such self-sustaining effect. In this case the catalyst was allowed to rise through reactants comprising 30-40% glycerol, and with the aid of a pH-sensitive dye that changes color in the presence of the reaction products, was observed to form a plume of reacted liquid, which became warmer and less dense than the original un-reacted fluid. To begin with the buoyancy of the reacted liquid surged upwards in a vertical conduit and widening plume head, but as the plume accelerated and reacted on the wider interface, the head "pinched off" as it gained momentum generating additional buoyancy. This led to a pooling of reacted liquid below that gained in volume forming a new plume head that repeated the process, detaching from the upwelling, leading to multiple generations of plume heads and a self-sustaining reaction.
"A supernova is a dramatic example of this kind of self-sustaining explosion in which gravity and buoyancy forces are important effects. We wanted to see what the liquid motion would look like in such a self-stirred chemical reaction," says Michael Rogers, who led the experiment as part of his PhD research, under the supervision of Morris. "The connection with supernovae comes because both involve reacting bubbles that rise under gravity," he explains, "but ours are pretty gentle and much smaller than real supernovae, obviously. The relevant form of supernova is a type Ia, in which a compact white dwarf star suddenly detonates due to a flame bubble nucleation process."
In fact the flame ball is buried deep inside the white dwarf, but being lighter than its surroundings rises rapidly creating a plume with an accelerating smoke ring. "It is extremely difficult to observe the inside of a real exploding star light years away so this experiment is an important window into the complex fluid motions that accompany such an event," said Morris. "The study of such explosions in stars is crucial to understanding the size and evolution of the universe."
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