A campfire that always blazes up to the same temperature — whether you toss a match into the center of a log or light several kindling sticks at the edges. That's roughly how Type Ia supernovas behave: cosmic explosions that astronomers use as rulers to measure distances across the universe.

For a long time, it was thought that such an explosion occurs when a white dwarf, the ultra-dense remnant of a star, siphons matter from a companion star and reaches a critical mass. But how exactly the detonation begins, the sudden explosive transition from relatively slow burning, remained a mystery. In the new study, scientists for the first time applied a mechanism that works not only in theory but has also been tested in terrestrial laboratories: the transition from burning to detonation driven by turbulence (tDDT). It's as if a fireplace flame suddenly accelerates into a supersonic shock wave due to chaotic air swirls.

The authors ran several scenarios, varying the density at the white dwarf's center and the shape of the initial burning region. The outcome surprised them: although the conditions differed by a factor of six, all models produced nearly identical spectra at peak brightness — the 'fingerprint' of the explosion. Moreover, this spectrum matched exactly that of the real observed supernova SN 1999aa. This result provides the first physical explanation for why Type Ia supernovas are so predictable: turbulence itself 'chooses' the same configuration for the explosion, just as a river always finds the shortest path to the sea.