A supernova is a stellar explosion, which occurs when the lives of some really massive stars come to an end. In this violent epilogue, the star expels the material from its outer layers by means of a shock wave, allowing us to see the various elements it was composed of. The research team developed a model of the gravitational field of the galaxy that acted as a lens, and that way it was possible to determine that the light from these three images travelled along three different paths, differing in distance by a few days. This accounts for the three colours obtained in the images because a variation in the colour emitted takes place as the gas in the supernova expands and cools. The higher the temperature is, the bluer the light emitted will be, and as the temperature falls, the light emitted tends towards red. So the blue image is a photograph of the supernova a few hours after the stellar explosion, while the green and red images correspond to 2 and 8 days, respectively, after the explosion.