Artist's conception of a Type Iax supernova. Source. Credit: Christine Pulliam
Researchers from the Harvard-Smithsonian Center for Astrophysics have discovered what they believe to be a new class of supernova. The two most common classes of supernovae are Type Ia and Type II supernovae. A Type Ia supernova occurs in binary star systems where a white dwarf star syphons too much matter from its neighbor and explodes from the increased energy and pressure. A Type II supernova occurs when a star much larger than our own burns through too much of its fuel and collapses in on itself, throwing out matter and radiation in a massive explosion as the pressure increases. A Type II supernova is much larger than a Type Ia supernova.
This new supernova, however, is smaller even than a Type Ia. They are so small that we didn't even know they existed until now. It's not entirely clear how they happen, but it is likely that a white dwarf in a binary system siphons off too much hydrogen from its companion, and then begins to suck away helium which then either begins to fuse, or which causes heavier elements to fuse and explode. Whatever the cause, Type Iax supernovae are small enough that the star can actually survive the explosion.