The solar flare of June 3, 2012 behaved like an orchestra where, after the main performance, a second soloist unexpectedly steps in. First, instruments recorded a sharp burst of gamma-ray emission with energies above 100 megaelectronvolts — as if billions of tiny bullets struck the detectors at once. Then, after a brief pause, the emission intensified again and persisted for more than eight minutes. Previously, this was thought to be unique to this flare, but it turned out that a similar 'second act' had been observed as early as 1982 and subsequently in more than forty solar eruptions.

The second wave of emission is known as late gamma-ray emission. It is produced when fast protons — hydrogen nuclei accelerated by the flare — catch up with the expanding plasma bubble (coronal mass ejection) and collide with its shock wave. The shock wave acts as a natural accelerator: it picks up particles and hurls them with even greater force, causing them to generate gamma-ray photons. The delay between the first and second waves exactly matches the time needed for protons to catch up with this bubble.

This result links two phenomena previously studied separately: solar flares and particle streams arriving at Earth from shock waves. It turns out that during powerful events, the Sun triggers both mechanisms, and late gamma-ray emission is the bridge between them. It is like a single furnace that first quickly warms the room, then continues to heat it through pipes for a long time.