When a bright spot flares up on a star, astronomers want to know how much energy was released into space. They used to picture a flare as a growing campfire: the area of the fire increases, but the heat remains the same. That made calculations simpler, but reality turned out to be different. A flare is more like an electric stovetop turned up to maximum: the heated area doesn't change, but the temperature jumps sharply.
Observations of the Sun and other stars have long shown that flare temperature is not constant. Yet in calculations, it was stubbornly assumed to be constant — around 10,000 degrees. The authors of this work abandoned that assumption. They took the temperature from models and tracked how it changes over time. It turned out that previous energy estimates could be off by a factor of ten.
Now astronomers can estimate flare energy more accurately even from single-color images. This is important for understanding how stars affect their planets — for example, their atmospheres and the potential for life. A flare, like a stovetop, first heats up and then cools down, and it's this process that we can now measure.
The TESS telescope, which monitors stellar brightness, has already recorded more than 50,000 flares — enough to test the new method on a huge sample.