Don't try this at home

Kyoto, Japan -- Explosions in the sky and explosions on land are literally worlds apart. A supernova and a land mine explosion don't seem like they would have much in common. But at the fine level, their mechanisms are not so different: the so-called cell structure appears at the smallest scale, which provides the most important criterion in predicting the success or failure of terrestrial detonation in a land-mine explosion. 

Terrestrial and astrophysical detonations are basically dictated by the same theories for their time-averaged characteristics. Terrestrial cell-based theories, however -- such as those that explain a land mine explosion -- have not yet been applied as criteria for astrophysical detonation.

Motivated by the potential of this theoretical analogy, an interdisciplinary research team of engineers and astrophysicists at Kyoto University recently joined together to better understand how type Ia supernovae explode.

A type Ia supernova occurs in a binary system in which one of the stars is a white dwarf. The primary mechanism behind this is detonation, a type of supersonic combustion that occurs either as the white dwarf reaches the critical mass by mass accretion or as the accreted material gets extremely heated, causing it to blow apart within seconds. Scientists generally agree that these supernovae are driven by a thermonuclear runaway process in the white dwarf, but discussion has continued on the exact cause of the detonation.

"It is not clear how detonation -- the key process in these supernovae -- is triggered," says corresponding researcher Keiichi Maeda.

Detonation was originally discovered in terrestrial explosions, and extensive theoretical research based on laboratory combustion experiments has established the criteria for its initiation and quenching. These criteria, widely used for designing detonation engines and preventing explosions, chiefly focus on the cellular structure.

In this study, the researchers simulated the cell structure in the context of a double-detonation model, in which the first event occurs in the helium-rich envelope of the white dwarf, subsequently triggering a secondary detonation in the core, which finally disrupts the star. They then observed the cellular structure in the primary detonation and acquired the cell width for each simulation, which they incorporated into terrestrial cell-based theories.

The results proved successful in confirming the analogy between the terrestrial and the astrophysical. When comparing their results with previous full-star simulations, the team observed that the thresholds of initiation and quenching of the primary detonation had been reproduced in agreement.

"It is particularly intriguing that terrestrial detonation experiments may contribute to an understanding of detonations in stellar media," says corresponding researcher Kazuya Iwata.

In addition to understanding the mechanisms behind type Ia supernovae, the study can also help explain the expansion of the universe. Because of their consistent luminosity, type Ia supernovae are often used as cosmological standard candles to measure distance in space.

"We will continue to explore unresolved scenarios of these supernovae by combining the viewpoints of terrestrial and astrophysical detonation," continues Iwata, who eagerly points out that, as an added bonus, this collaborative project has also demonstrated the importance of interdisciplinary interaction between science and engineering.