There is a lot that we don’t understand about supernovae. We know what causes them and broadly what goes on, but the exact details are still unclear. Type II supernovae, for example, happen when massive stars run out of fuel and undergo a rapid collapse before producing a violent explosion.
These events should be “announced” by a bright flash of light called a shock breakout, an impressive brightening of the star before its fateful final explosion. In a series of observations, researchers from the University of Chile tried to study this phenomenon but they weren’t actually able to detect it in any of the 26 Type II red giant supernovae in their survey. Interestingly, 24 out of the 26 supernovae in the sample appeared to become brighter more quickly than expected. The findings are published in Nature Astronomy.
To clarify what was going on, the team led by the University's Francisco Förster brought in Takashi Moriya from the National Astronomical Observatory of Japan (NAOJ). Moriya simulated 518 different Type II supernovae and the team compared the observation to this virtual catalog of objects. The simulation suggests that the key to explaining these events is found before the supernovae actually explode.
The supernovae that brightened quickly with no shock breakout seem to be shrouded by a lot of material. According to the model, these objects have about one-tenth of the mass of the Sun surrounding them, which is enough matter to hide the shock breakout. However, it also responsible for causing the quick brightening. When the star explodes, the shockwave hits this material, producing more light.
"Near the end of its life, some mechanism in the star's interior must cause it to shed mass that then forms a layer around the star," Moriya explained in a statement. "We don't yet have a clear idea of the mechanism causing this mass loss. Further study is needed to get a better understanding of the mass loss mechanism. This will also be important in revealing the supernova explosion mechanism and the origin of the diversity in supernovae."
The results significantly expand our understanding of late stellar evolution. And while they didn’t observe the shock breakout, it is not impossible for us to see it. A lucky amateur astronomer was able to snap a picture of it while testing their brand new camera earlier this year.