Thirty-six years ago, a star exploded in a neighboring galaxy. The flash was named Supernova 1987A, and since then it has been monitored almost every year. Now the James Webb Space Telescope has looked at its remnant in the mid-infrared — the part of the spectrum where dust and heated gas glow. The previous measurement was made a year ago, and comparing the two images shows how quickly this cosmic construction site is changing.
The main stage is a ring of gas and dust that the star shed before the explosion. The inner edge of the ring is dimming, while the outer edge is brightening. It's like someone slowly moving a lamp toward a wall: first the nearest part is brightest, but as the lamp approaches, the light shifts further along. Here, the lamp is played by the shock wave from the explosion, which is catching up with the ring and heating its increasingly distant parts.
Another piece of news: iron emission lines show that the dense inner material of the star has finally reached the reverse shock wave traveling inward. This is a crucial moment, like two streams meeting on a highway, after which the pattern of motion changes dramatically. Now astronomers are waiting to see how this encounter will reshape the glow of the entire supernova remnant.
A year after the first infrared portrait, the picture has changed, but not drastically. The dust in the ring has barely evolved, but the lines from the ejected gas are changing rapidly. This means the main events are still ahead, and the James Webb Space Telescope will need to return to this star many times. After all, it is from such dust and gas that new stars and planets will eventually form.
Light from Supernova 1987A traveled 168,000 years to reach Earth — the same amount of time that separates us from the appearance of the first Homo sapiens.