Scientists have debuted a theory using the explosions seen in industrial accidents to understand supernovae in a new paper.
Destructive explosions typically involve several different kinds of processes: deflagration, or flames igniting a medium slower than the speed of sound, and detonation, faster-than-sound shockwaves compressing and igniting the fuel Initiating a detonation hard, especially in a system without any confining boundaries—like an open-air industrial accident or, say, a supernova. Using simulations, theory, and even an experiment, the scientists realised that flames interacting with an intensely turbulent environment can set off one of these unconfined detonations, though.
The study’s first author Alexei Poludnenko from the Texas A&M started out as an astrophysicist by training, working on a longstanding problem in our understanding of supernova: how does an unconfined ball of gas detonate, without the force just whiffing it away? But when an oil storage facility in U.K. blew up in 2005, the detonation almost acted like the unconfined detonations in space.
“My thinking was that maybe astrophysicists weren’t talking to combustion physicists who deal with these things every day,” Poludnenko told Gizmodo.
He and others began working on a unified theory of these explosions, and began running numerical models simulating unconfined explosions on supercomputers. By 2011, the team showed how a deflagration could turn into a detonation in an unconfined system: chaotic flows of the flames caused them to burn faster than a characteristic speed, setting off quick pressure changes that produced shockwaves. But in order for these flames to maintain a detonation and cause a runaway increase in pressure necessary for a shockwave, the turbulence must be enough to pack the flamelets into a tight enough characteristic volume.
The researchers had their theory and modelled it on supercomputers, but they still didn’t have any experimental evidence to back up their work. Unfortunately, it’s hard to create and observe an unconfined experiment in an explosion. Poludnenko joined up with researchers at the University of Central Florida to perform experiments in a shock tube that measured 1.5 metres long and 4.5 centimetres wide with one open end and one closed end. The tube also had windows on each side to observe the behaviour. Though it wasn’t quite an environment for an unconfined explosion, the researchers thought they could isolate just the region where turbulent flames would produce the pressures required to set off an ignition, according to the paper published in Science.
The team filled the tube with a mixture of hybrid and air and ignited it using a spark plug. Flames travelled down the tube, and plates with holes in them inside the tube generated turbulent flow. This produced a shockwave travelling two to three times the speed of sound at the open end. The researchers observed through the window as the flames turned into a detonation, behaving as predicted by their theoretical work and simulations.
With experimental data to combine with their simulations and theory work, the researchers felt they’d produced a unified mechanism for these kinds of explosions, called the turbulence-driven deflagration-to-detonation transition, or tDDT. They used it to produce numerical models for thermonuclear explosions, and finally to calculate the properties that would cause such a runaway event in supernovae. At the incredible densities inside the core of supernovae, a deflagration to detonation transition is “almost inevitable,” the authors write.
As for who might care about such a theory, the research was funded by NASA, the Air Force, and the Alpha Foundation for the Improvement of Mine Safety and Health, with computing resources provided by the Department of Defence and the Naval Research laboratory.
It’s a “really important paper,” Craig Wheeler, emeritus professor of astronomy at the University of Texas at Austin not involved in the study, told Gizmodo, and a “major step” linking the easier-to-compute terrestrial conditions with much harder-to-test supernovae. He pointed out that this paper’s consequences would be important enough that people in the field might need to rethink their understanding of supernovae—so it’s worth a few more teams looking at it to ensure that it’s right.
This experiment is still far from actually watching a supernova detonation play out up close, but the researchers hope that better observations of supernova and the elements they emit would let them better understand how stars undergo detonations, according to the paper.
Explosions are an important part of our lives—cars and planes run on combustion engines, and hey, sometimes it feels like our entire lives can be uprooted by an explosion, both physical and metaphorically, at any moment.
But this study shows that even our earthly detonations might be important for our greater understanding of the cosmos.