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Stars and solar physics

Stars and solar physics

Supernovae and earthbound chemical explosions are surprisingly similar

19 Nov 2019
Fireworks
Ka-boom: these fireworks explode in the same way as white-dwarf stars. (Courtesy: iStock/PorFang)

Despite their enormous differences in size, type 1a supernovae and chemical explosions on Earth detonate via similar physical mechanisms – according to a team led by Alexei Poludnenko at Texas A&M University and the University of Connecticut. The researchers uncovered the similarity by comparing computer simulations of stellar explosions with observations of chemical detonations. Their discovery could provide new insights into the poorly understood processes of supernovae explosions.

A type 1a supernova (SN1a) is thought to occur when a white-dwarf star in a binary system acquires enough material from its companion star to reach a critical mass — at which point a runaway thermonuclear fusion reaction causes the star to explode. Beyond this basic description, however, a more complete understanding of the mechanics involved in SN1a explosions is lacking – and several different theoretical models of SN1a remain equally plausible.

Most theories of SN1a assume that the huge explosion is triggered by the formation of a supersonic detonation wave that causes the thermonuclear burning of all stellar material it encounters as it expands. Yet the processes that initiate detonation are poorly understood in unconfined systems like white-dwarf interiors. These systems are extremely difficult to describe using numerical models because they involve physics that occurs over a wide range of scales. Ultimately, this limits the predictive power of existing SN1a models.

Subsonic to supersonic

Poludnenko and colleagues sought to overcome this challenge by focussing on similarities between the thermonuclear combustion waves characteristic of SN1a, and the chemical combustion waves found in Earth-based explosions. In both cases, a transition occurs from deflagration (where combustion moves at subsonic speeds) to detonation (combustion moving at supersonic speeds).

This transition is believed to be driven by high-intensity turbulence in both chemical explosions and SN1a. To study the similarities, the team first developed a theory of how turbulence drives the transition from deflagration to detonation, which they then confirmed using experimental data from hydrogen explosions. Then they used the theory to develop a computer simulation of how the same process would occur in a SN1a – and looked for parallels between the stellar and chemical explosions.

Their study has provided important insights into how thermonuclear combustion waves in SN1a make the transition to detonation. Ultimately, this could make it far easier for astrophysicists to predict how the dynamics of the stellar explosions will unfold over time.

The research is described in Science.

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