Flash-in-the-pan supernovas explained
Most exploding stars flare brightly and then slowly fade over weeks to months, but an unusual group of supernovas noticed only in the last 10 years flare up and disappear within days.
Thanks to the ability of NASA’s Kepler Space Telescope to precisely measure starlight over long periods of time, astronomers now have a pretty good idea what these flash-in-the-pan supernovas are: exploding stars probably too dim to be detectable until the stellar matter ejected during the explosion collides with a shell of material puffed off years earlier by the star.
The collision generates a shock wave that heats up the shell of gas, but then rapidly fades. While supernovas continue to glow because of the radioactive material generated in the explosion, these shocked clouds contain little radioactive material and have no residual glow.
This interpretation for what have been called fast-evolving luminous transients, or FELTs, comes from models created by University of California, Berkeley astrophysicists that match closely the observed light from a recently recorded supernova dubbed KSN2015K.