What do you do when you see the flash? In the case of a dying star, you know a supernova is coming.
A core-collapse supernova occurs when a large star runs out of hydrogen and other elements to fuse. The fusion of elements in a star’s core creates the heat and pressure necessary to prevent a star from collapsing under its own weight. When a star stops fusing elements, its core cools rapidly and collapses. The heavy elements in the core slam into each other and recoil, creating a shockwave that rips the star apart. This causes a dramatic brightening of the star over a period of days, which is what we observe as a supernova. But before the star explodes the shockwave ripples through the layers of the star. It first causes instabilities in the star’s surface, such as plasma jets. When the full shockwave reaches the surface, it liberates a tremendous amount of photons from the star’s interior, causing an initial flash of light before the star begins to brighten.
At least that was the theory. The problem is the initial flash only lasts a few minutes, and it occurs before the star swells into a supernova. Usually we don’t notice a supernova until the star has already brightened a bit. To see the initial shockwave flash, you need to be watching a star before it goes supernova. Since we have no way of predicting when a particular star will begin to explode, we haven’t been able to catch the initial flash. That is, until now, when the Kepler space observatory happen to observe a supernova in its earliest moments.
The Kepler space observatory was designed to find exoplanets. It does this by observing stars for long periods of time, measuring their brightnesses to look for small dips in brightness. Such dips can indicate that a planet is passing in front of the star. It just so happened that a star in its field of view began to go supernova, and so Kepler caught the initial flash of the shockwave. It was really just blind luck, but it confirms the shockwave of a core-collapse supernova.
As we continue to make large scale sky surveys, the chances of observing the early stages of a supernova such as this become more likely. That’s important because it’s only by studying the early stages of a supernova that we will gain a better understanding of their triggering mechanisms.