Article Posted on : - Dec 20, 2013

An unrelated ESO photo

WASHINGTON (PTI): Astronomers have discovered two of the brightest and most distant supernovae ever recorded, 10 billion light-years away from Earth, which are hundred times more luminous than a normal supernova.

These newly-discovered supernovae are especially puzzling because the mechanism that powers most of them - the collapse of a giant star to a black hole or normal neutron star - cannot explain their extreme luminosity.

Discovered in 2006 and 2007, the supernovae were so unusual that astronomers initially could not figure out what they were or even determine their distances from Earth.

"At first, we had no idea what these things were, even whether they were supernovae or whether they were in our galaxy or a distant one," said lead author D Andrew Howell, a staff scientist at Las Cumbres Observatory Global Telescope Network (LCOGT) and adjunct faculty at University of California - Santa Barbara.

One of the newly discovered supernovae, named SNLS-06D4eu, is the most distant and possibly the most luminous member of an emerging class of explosions called superluminous supernovae.

The new study finds that the supernovae are likely powered by the creation of a magnetar, an extraordinarily magnetised neutron star spinning hundreds of times per second.

While a handful of these superluminous supernovae have been seen since they were first announced in 2009, and the creation of a magnetar had been postulated as a possible energy source, the work of Howell and his colleagues is the first to match detailed observations to models of what such an explosion might look like.

Co-author Daniel Kasen from UC Berkeley and Lawrence Berkeley National Lab created models of the supernova that explained the data as the explosion of a star only a few times the size of the sun and rich in carbon and oxygen.

The star likely was initially much bigger but apparently shed its outer layers long before exploding, leaving only a smallish, naked core.

"What may have made this star special was an extremely rapid rotation. When it ultimately died, the collapsing core could have spun up a magnetar like a giant top. That enormous spin energy would then be unleashed in a magnetic fury," Kasen said.

The two supernovae were discovered as part of the Supernova Legacy Survey (SNLS) - a five-year programme based on observations at the Canada-France-Hawaii Telescope, the Very Large Telescope (VLT) and the Gemini and Keck telescopes to study thousands of supernovae.

It took subsequent observations of the faint host galaxy with the VLT in Chile for astronomers to determine the distance and energy of the explosions.

The supernovae exploded when the universe was only 4 billion years old, researchers said.

The study will be published in the Astrophysical Journal.