In this negative image of the Pinwheel Galaxy (M101), red squares mark the positions of "super-soft" X-ray sources. The Pinwheel should contain hundreds of accreting white dwarfs on which nuclear fusion is occurring, which should produce prodigious X-rays. Yet detected are only a few dozen super-soft X-ray sources.

Why certain stars explode in supernovas is a mystery to scientists, and a new study finds the situation is even murkier than thought because some of the light from these stars may be blocked.

To understand more about these cosmic explosions, astronomers are hunting for ticking time bombs stars that are on the track toward becoming supernovas. Yet the missing light could make the search even harder.

Death of a star

Supernovas mark the death of a star, when it stops shining light created through nuclear fusion and instead collapses into an extremely dense black hole.

A subset of supernovas called Type Ia supernovas are the gold standard in astronomy. They are thought to erupt when a dense, dim star called a white dwarf hits a certain upper limit in mass and explodes.

Thus, each white dwarf erupting in a Type Ia supernova will shine at roughly the same brightness. This allows astronomers to spot them across the universe and tell how far away they are by how bright they appear, compared to their known intrinsic luminosity. (They are called "standard candles," for this special distance measuring feature.)

But astronomers are still confused by just what cases white dwarfs to hit that mass limit and explode. MSNBC