Closest Type Ia Supernova in decades solves a cosmic mystery

The Palomar Transient Factory caught SN 2011fe in the Pinwheel Galaxy in the vicinity of the Big Dipper on Aug. 24, 2011.

Found just hours after it exploded and only 21 million light years away, the discovery triggered the closest-ever look at a young Type Ia supernova. Credit: Image by B. J. Fulton, Las Cumbres Observatory Global Telescope Network

Type Ia supernovae (SN Ia's) are the extraordinarily bright and remarkably similar "standard candles" astronomers use to measure cosmic growth, a technique that in 1998 led to the discovery of dark energy – and 13 years later to a Nobel Prize, "for the discovery of the accelerating expansion of the universe."

The light from thousands of SN Ia's has been studied, but until now their physics – how they detonate and what the star systems that produce them actually look like before they explode – has been educated guesswork.

On August 24 of this year, searching data as it poured into DOE's National Energy Research Scientific Computing Center (NERSC) from an automated telescope on Mount Palomar in California, Peter Nugent spotted a remarkable object.

It was shortly confirmed as a Type Ia supernova in the Pinwheel Galaxy, some 21 million light-years distant. That's unusually close by cosmic standards, and the nearest SN Ia since 1986; it was subsequently given the official name SN 2011fe.

Nugent says, "We caught the supernova just 11 hours after it exploded, so soon that we were later able to calculate the actual moment of the explosion to within 20 minutes.

Our early observations confirmed some assumptions about the physics of Type Ia supernovae, and we ruled out a number of possible models. But with this close-up look, we also found things nobody had dreamed of."

"When we saw SN2011fe, I fell off my chair," says PTF team member Mansi Kasliwal of the Carnegie Institution for Science and the California Institute of Technology.

"Its brightness was too faint to be a supernova and too bright to be nova. Only follow-up observations in the next few hours revealed that this was actually an exceptionally young Type Ia supernova."