It was the brightest and closest stellar explosion seen from Earth in 25 years, dazzling professional and backyard astronomers alike.

Now, thanks to this rare discovery—which some have called the “supernova of a generation” — astronomers have the most detailed picture yet of how this kind of explosion happens.

Known as a Type Ia supernova, this type of blast is an essential tool that allows scientists to measure the expansion of the universe and understand the very nature of the cosmos.

On August 24, the Palomar Transient Factory (PTF) team discovered the supernova in one of the arms of the Pinwheel Galaxy (also called M101), 21 million light years away. They caught the supernova just 11 hours after it exploded.

“Never before have we seen a stellar thermonuclear explosion so soon after it happened,” says Lars Bildsten, professor of theoretical astrophysics at the Kavli Institute for Theoretical Physics at UC Santa Barbara, and member of the PTF team, which described its supernova findings today (December 15) in Nature.

The PTF team uses an automated system to search for supernovae, and because they were able to point their telescopes at SN2011fe so quickly after its detonation, the astronomers were able to put together a blow-by-blow analysis of the explosion, determining that the supernova involves a dense, Earth-sized object called a white dwarf and, most likely, a main-sequence star (a star in the main stage of its life), according to a University of California, Santa Barbara press release.

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