Weighing Titanium in a Supernova express
When a massive star explodes as a supernova, heavy nuclei are forged in its interior within seconds. Among them is titanium-44, a radioactive isotope that later glows in gamma rays for years. How much of it remains depends on a single nuclear reaction: a proton is captured by a vanadium-45 nucleus, turning it into chromium-46. This is like a narrow doorway through which some titanium leaks out of the synthesis chain.
Recently, physicists measured this reaction directly for the first time, but the accuracy was limited by the mass of chromium-46. Now, with a new mass value that is four times more precise, the reaction rate at stellar explosion temperatures has increased to 69%. In a supernova model with a mass of 20 solar masses, this yields 26% more titanium-44 in the ejected material.
Interestingly, for supernova 1987A, the changes are almost negligible. It all comes down to the composition of the ejecta: if there are many free protons, the reaction proceeds actively, but if the material is richer in neutrons, protons are scarce and the door is nearly shut. So titanium-44 is sensitive to how 'proton-rich' the explosion was.
Titanium-44 decays with a half-life of about 60 years — a blink of an eye by astronomical standards, but enough for a supernova remnant to glow in gamma rays for decades.