Explosive Origins of Recently Discovered 'Superluminous' Supernova Still a Mystery

Scientists recently discovered an exotic "superluminous" supernova, brighter than any other normal supernova, but the origins of its extraordinarily luminescent explosion still remain a mystery.

The Dark Energy Survey (DES), which first began in August 2013, captured images of this rare supernova that erupted in a galaxy 7.8 billion light years away. The stellar explosion, called DES13S2cmm, easily outshines most galaxies in the Universe and could still be seen in the DES data six months later.

Supernovae are typically very bright, and shine up to a few billion times brighter than the Sun for weeks on end. Superluminos supernovae, however, outdo even the brightest usual supernovae - they glow 10 to 50 times brighter than average.

These rare cosmic explosions were just recognized within the last five years, so scientists are just beginning to understand them, let alone their origins.

"Fewer than forty such supernovae have ever been found and I never expected to find one in the first DES images!" Andreas Papadopoulos, a postgraduate student from the University of Portsmouth who made the discovery, said in a statement. "As they are rare, each new discovery brings the potential for greater understanding - or more surprises."

It turns out that even within this select group, DES13S2cmm is unusual. The rate that it is fading away over time is much slower than for most other known superluminous supernovae. This change in brightness over time, or "light curve," gives scientists a clue about the underlying mechanisms that caused the explosion as well as the composition of ejected material.

Led by Dr. Mark Sullivan of Southampton University, researchers obtained spectroscopy of DES13S2cmm using the Very Large Telescope at Cerro Paranal, Chile (work is currently being done to construct Chile's other massive telescope, the European Extremely Large Telescope).

They speculate that radioactive decay, which is known to power normal supernovae, may be the source, but that theory is still controversial.

"We have tried to explain the supernova as a result of the decay of the radioactive isotope Nickel-56," explained co-author Dr. Chris D'Andrea, "but to match the peak brightness, the explosion would need to produce more than three times the mass of our Sun of the element. And even then the behavior of the light curve doesn't match up."

For now, the team is investigating other options, such as a magnetar core - an exotic neutron star spinning hundreds of times per second, producing a magnetic field a trillion times stronger than that on Earth.

DES will start the second of what will be five years of observing in August, hunting for more superluminous supernovae.

The discovery is being presented at the National Astronomy Meeting 2014 in Portsmouth on Wednesday, June 25.