There are billions of trillions of stars in our cosmos (yes, that’s a huge and incomprehensible number). These stars are continuously burning fuel (mostly hydrogen) to exist. When this fuel runs out, some stars explode into what is known as a Supernova, a massive stellar explosion. Some supernovas are so bright that they can outshine their parent galaxy. Visual observations and theoretical modelling predicts that supernovae explosions happen when carbon and oxygen packed to a density of around 1,000 tons per cubic centimetre in the star’s core burn in quick, thermonuclear reactions. The resulting explosion disrupts a star in a matter of seconds and ejects most of its mass while emitting an amount of energy equal to the energy emitted by the star over its entire lifetime. However, the physical mechanism that triggers this explosion is poorly understood.
Scientists have now come up with a theory on how this explosion is triggered (1). By performing numerical simulations and laboratory experiments, researchers from the University of Connecticut were able to reproduce a supernova like explosion.
Typically, in order to form a detonation, burning must occur in a confined setting with walls, obstacles, or boundaries, which can confine pressure waves being released by burning.
As pressure rises, shock waves form, which can grow in strength to the point when they can compress the reacting mixture igniting it and producing a self-sustaining supersonic front. Stars do not have walls or obstacles, which makes the formation of a detonation enigmatic.
In this study, the team developed a unified theory of turbulence-induced deflagration-to-detonation that describes the mechanism and conditions for initiating detonation both in unconfined chemical and thermonuclear explosions.
According to the theory, if one takes reactive mixture, which burns and releases energy, and stirs it up to create intense turbulence, a catastrophic instability can result and would rapidly increase pressure in the system producing strong shocks and igniting a detonation. Remarkably this theory predicts the conditions for detonation formation in Type Ia supernovae.
Researchers were able to gain insight into the fundamental aspects of the physical processes that control supernovae explosions because thermonuclear combustion waves are similar to chemical combustion waves on Earth in that they are controlled by the same physical mechanisms.
Because of the similarities, the findings may be applied to various terrestrial combustion systems in which detonations can form, such as the context of industrial accidents involving gaseous explosions, as well as novel propulsion and energy conversion applications, such as detonation-based engines.
- 1.A. Poludnenko, J. Chambers, K. Ahmed, V. Gamezo, B. Taylor, A unified mechanism for unconfined deflagration-to-detonation transition in terrestrial chemical systems and type Ia supernovae. Science. 366 (2019) (available at https://www.ncbi.nlm.nih.gov/pubmed/31672866).