A closer look
The element technetium has no stable isotopes, meaning any trace of it in the universe is a loud, glowing fingerprint of recent cosmic violence. Because technetium decays incredibly fast on a cosmic scale, its discovery in the spectral light of asymptotic giant branch stars was a massive shock to astronomers. It proved stellar nucleosynthesis was actively happening. Deep inside these dying red giants, the slow neutron-capture process bombards lighter atoms, fusing them into heavier, radioactive elements right before the star violently ejects its guts.
