Stars can come back from the dead, then explode

 Because they're fairly frequent (each galaxy hosts one once ever few hundred years), findable and predictable, type 1a supernovae are often called "cosmic mile markers" or "standard candles" by astronomers.
A type 1a supernova is the name given to the brief but deadly last hurrah of a white dwarf. A white dwarf is a dying star, a shell of its former self -- a star that has shrunken in size, decreased in temperature and has long since shed its powerful, temperamental outer layers. But during a type 1a supernova, a white dwarf momentarily springs back to life. It burns hard and bright, swells in size, and then explodes.
At least that's what scientists had always assumed to happen. Until now, their evidence has been mostly circumstantial -- the origins of "standard candles" still shrouded in mystery. But earlier this year, astronomers were able to observe a type 1a supernova in as close as one can get to real-time.
Scientists had long surmised that type 1a supernovas would shoot out gamma rays created as a an exploding white dwarf ejected bits of iron, cobalt, and nickel. But these gamma rays start off so far away from Earth, they get lost and swallowed up by space before scientists her can detest them.
But earlier this year, European Space Agency's INTEGRAL satellite detected gamma rays emitted from a nearby (11.5 million light-years away) supernova. Scientists at the University College London were able to use the gamma rays to work backwards and trace its origins to an exploding white dwarf in the Cigar Galaxy.
"The importance of this discovery is not because something new/unknown was discovered, but we had an observation of a long-standing theory that had no real evidence," Brad Tucker, a researcher at both UC Berkeley and Australian National University, recently told National Geographic's Nadia Drake. "Knowing that our fundamental physics is correct is an important thing."
The discovery is detailed in the latest edition of the journal Nature.
The discovery offers affirmation for previously unverifiable theories -- mainly that a type 1a supernova is the result of a white dwarf that becomes unstable after it takes on new matter, triggers nuclear fusion, exceeds its Chandrasekhar limit (named after the Indian-American astrophysicist Subrahmanyan Chandrasekhar) and implodes. But it still can't explain exactly where the extra weight and matter comes from.
"It is perfectly consistent with the simplest scenario, of a single white dwarf with a mass close to the Chandrasekhar limit," lead researcher Eugene Churazov told the BBC. "But we cannot exclude with this data that this event was caused by a merger [of two white dwarfs]."