When a heavy nucleus slams into interstellar gas at enormous speed, it shatters into pieces. Those pieces (lithium, beryllium, boron) then fly onward, and their abundance in the cosmic-ray flux depends on how the breakup unfolded. Conventionally, one expected the proportions to shift smoothly with energy, like the taste of soup when you keep adding water.

But the AMS-02 detector on the International Space Station showed something else. Starting at energies around 30 GV (enough to push a particle to 0.999 times the speed of light), the ratios of lithium to beryllium, beryllium to boron, and lithium to beryllium stop changing altogether. They freeze, like the needle of a scale when the pans are balanced. This doesn't fit older models, where everything depends on a host of fine details.

The authors suggest looking at the process differently. When a nucleus breaks apart, the remnant decelerates sharply, like a car hitting a wall. Under such deceleration, according to ideas akin to black-hole physics, heating occurs with a temperature around 5.6–5.8 MeV (hundreds of billions of times hotter than room temperature). Using the beryllium-to-boron ratio as a calibration, they obtain a temperature of 6.08 MeV — nearly the same. And this temperature matches the threshold at which nuclear matter ceases to be a liquid and becomes a gas.

Checks on the lithium ratios confirmed: the slope of the curves becomes zero. This means that at high energies, there's no need to account for the complex microscopic kitchen — a single constant temperature suffices. Such a simple law could greatly simplify data analysis and reduce errors in determining cosmic-ray composition.

The frozen proportions are like a perpetual noon settling over a fast-moving stream of debris: the temperature neither rises nor falls but holds at a single mark, set by the very geometry of the breakup.