November 2, 2012
Astronomers Locate Two Distant Super-Luminous Supernovae
April Flowers for redOrbit.com - Your Universe Online
An international team, including Raymond Carlberg of the University of Toronto's Department of Astronomy & Astrophysics, has discovered the most-distant, super-luminous supernovae observed to date. The violent stellar explosions which caused these supernovae would have occurred soon after the Big Bang when the universe was much younger.
"The objects are both unusually bright and unusually slow to fade. These are properties that are consistent with what is known as pair-instability supernova, a rare mechanism for explosion which is expected to happen for high-mass stars with almost no metal content. That is, the very first stars to form," said Carlberg.
The Canada-France-Hawaii Telescope Legacy Survey provided the image data that allowed the team to identify the two supernovae, named SN2213 and SN1000+2016. Various surveys conducted in recent years have enabled astronomers to view the universe in new exquisite detail, including the discovery of super-luminous supernovae, over the last decade, that are tens to hundreds of times more luminous than regular supernovae.
"The Canada-France-Hawaii Telescope Legacy Survey stands out as the first really deep survey of the sky, covering large volumes of the universe," said Carlberg, a leader of the Survey.
The Canada-France-Hawaii Telescope Legacy Survey was a dedication of 2300 hours of observation over five years using dark and grey telescope time in both Canada and France. The Survey used the MegaCam, a wild field optical imaging 340-megapixel camera. The final official release of data was delivered October 26, 2012. The findings of this study will be published in the November 8 issue of Nature.
The team processed the image data at the University of Toronto using a search technique to first narrow the search to the high redshift star-forming galaxies. Then they looked for supernovae that are both more luminous than normal and have unusually long fading times. These criteria are precisely the characteristics of pair-instability supernovae.
Stars that have 150 — 300 times the mass of our Sun are the only place that the pair-instability explosion mechanism occurs. Stars that massive do not form in the current universe. As stars form, they start nuclear burning and push away additional gas. In the early days of the universe, however, the metal abundance of the gas is essentially zero. This makes the gas almost transparent so that it can fall on the forming star.
Massive stars formed this way do not last long because they are so hot in the center that pressure is lost causing a collapse to start. This heats up the core even more and eventually, enough oxygen and silicon are created so that their fusion causes a nuclear explosion. This explosion is much more luminous than other supernovae mechanisms.