Black holes hurl stars out of galaxy, after which they explode

On the simplest level, there are only two types of supernovae: those caused when a massive star collapses and those caused when white dwarf stars reach a critical mass. But the better we're able to image supernovae, the more we're finding out that there are distinct subtypes within each of these classes. Or, as the author of a new paper put it, "It turns out that there were about a dozen new classes of ‘exotic’ or ‘peculiar’ transients lurking in the shadows."

Figuring out the physics that creates these peculiarities can be a significant challenge. But the paper provides a possible explanation for something called a "calcium rich supernova." And the explanation involves a binary star system being hurled from its galaxy by a pair of supermassive black holes.

The first instance of these supernovae was recorded in 2005, and while they're rare, they still occur at about five percent the rate of the more common type Ia supernovae. As more of these events have been identified, a strange pattern became clear: they tend to occur far from a galaxy—on the order of 100,000 light years away or more. This led to the suggestion that they were occurring in dwarf galaxies or globular clusters, which would be hard to spot at great distances.