Cause of supernova explosion of year 1006 revealed

The supernova explosion of the year 1006 – the brightest stellar event ever recorded in history – was probably caused by the merger of two white dwarf stars, scientists have found.

Updated: Sep 28, 2012, 14:13 PM IST

London: The supernova explosion of the year 1006 – the brightest stellar event ever recorded in history – was probably caused by the merger of two white dwarf stars, scientists have found.

The supernova SN 1006, which occurred between 30 April and 1 May of the year 1006, was widely observed by different communities of astronomers all over the world.

Some of them, including Chinese astronomers, highlighted the fact that the astronomical event was visible for three years. The most explicit record, made by the Egyptian doctor and astronomer Ali ibn Ridwan (988-1061), notes that the phenomenon was about three times brighter than Venus, and that it emitted light of a quantity equivalent to almost a quarter of the Moon’s brightness.

Now, more than a thousand years later, a team led by researchers from the University of Barcelona, the Instituto de Astrofísica de Canarias (IAC) and the CSIC has revealed the cause of the brightest stellar event.

As co-director of the work, Pilar Ruiz-Lapuente, a researcher at the Institute of Cosmos Sciences (ICCUB) and the Instituto de Fisica Fundamental (IFF-CSIC), explained, “In this work the existing stars in the area have been studied, regarding distance and possible contamination by elements of the supernova, and the results show that there is no star that could be considered the progenitor of this explosion”.

The IAC researcher and first author of the paper Jonay Gonzalez Hernandez added, “We have conducted an exhaustive exploration of the area around where the explosion of the supernova of 1006 occurred and have found nothing, which invites us to think that this event was probably the result of a collision and merger of two white dwarf stars of similar mass”.

The supernova SN 1006 is of the type that occurs in binary systems, those consisting of two astronomical objects bound together by their gravitational pull. These systems can be formed by a white dwarf and a normal stellar companion that contributes the matter necessary for it to reach a critical mass of 1.4 times the mass of the Sun, the so-called Chandrasekhar limit.

Once this mass is reached, the stars explode in a supernova. Another possibility is that the system comprises two white dwarfs that eventually merge to create a supernova.

“This new result, together with others previous, suggests that the merger of white dwarfs could be a common pathway that leads to these violent thermonuclear explosions,” said Ruiz-Lapuente.

The final clue that led the researchers to conclude that in this case there had been a merger of two white dwarfs was that this supernova, about 7,000 light-years from Earth, has no stellar companion to the white dwarf progenitor.

However, an explosion produced by the merger of two white dwarfs leaves no trace, except for the supernova remnant that can be studied until centuries later, as in the case of SN 1006, one of only four historical supernovae of this type that have occurred in the Milky Way.

The study utilized an UVES high-resolution spectrograph installed in one of four European VLT telescopes, of 8 meters in diameter, belonging to the European Southern Observatory (ESO, Chile), with which the stars around the site of the explosion were observed.

The spectroscopic and photometric data obtained were analyzed in detail by González Hernández: “Analysis of the stars in the area of the explosion discarded them as possible companions of the progenitor star of the supernova of 1006”, said the expert.

The finding has been published in latest edition of the international science journal Nature.