http://phys.org/news/2012-09-brightest- ... id-ia.html
SN 1006 Supernova Remnant. Credit: NASA, ESA, Zolt Levay (STScI)
Over a thousand years ago, an explosion in faraway space occurred that was so bright that people reported being able to read by its light at midnight. The year was 1006 and the explosion was, scientists believe now, a supernova, or more accurately, a type Ia supernova, the kind that produce the biggest or brightest explosions. But what kind of Ia supernova was it? Astrophysicists believe there are two kinds, those that happen slowly, and those that happen very rapidly. Now new research by a team in Spain suggests it was the latter after scanning the area of sky where the explosion is believed to have occurred and not finding any evidence of a companion star left behind, which would indicate a slow moving event. They have published a paper describing their study in the journal Nature.
Type Ia supernovae come about, scientists believe, when a white dwarf star and a companion, such as a red giant, main-sequence giant, subgiant or even another white dwarf comingle, with the first accreting material from the second until sufficient mass is attainted to set off a thermonuclear explosion. They also believe that the process occurs in two ways, the first is where the two stars are both white dwarves, and they merge creating an explosion so powerful that both are obliterated. The second is where the first pulls material from the second rather slowly, and then explodes, leaving the companion behind.
In this new research the team scanned the area where the supernova, dubbed SN 1006 in honor of the year it was observed, was thought to have occurred, looking for a companion star, which would indicate the explosion (which some believe might be the brightest even seen by human beings) was the slow happening kind. They report that no such companion star exists in the area and thus SN 1006 must have been a rapid variety type Ia supernova.
The new finding would mean that there are now five documented type Ia super novae, with four being the rapid kind and just one the slow, leading the research team to suggest that perhaps only twenty percent of all such explosions are of the slow moving variety, which matters because astrophysicists use such explosions to calculate how fast the universe is expanding, which in turn impacts theories on dark energy, which appears to cause the expansion to speed up.