SN 1006

SN 1006 was a massive stellar explosion known as a supernova. It is likely the brightest stellar event ever recorded in human history. This explosion reached an estimated visual magnitude of −7.5. That makes it roughly sixteen times brighter than the planet Venus. The event appeared in the constellation Lupus. Scientists believe the explosion happened about 7,200 light-years from Earth. This distance is also described as 2,200 parsecs.

Astronomers believe this was a Type Ia supernova. This specific type of explosion happens when two white dwarf stars merge. A white dwarf is a small, dense star. In a "double degenerate" system, these two stars collide and destroy each other. This process completely disrupts the progenitor stars. Because the stars are entirely destroyed, no neutron star or black hole is left behind. Instead, the explosion leaves a massive shell of gas called a supernova remnant.

The explosion went through two distinct phases of evolution. First, there was a three-month period where the star was at its brightest. After this, the light diminished significantly. Then, the brightness returned for another period of about eighteen months. The star appeared to be a stationary, "tail-less" object. The Iranian philosopher Ibn Sina reported that the star even seemed to throw out sparks. He also noted that its color changed over time.

Many people around the world recorded this "guest star" in 1006. Observers in China, Japan, Iraq, Egypt, and Europe all saw it. In Egypt, the astronomer Ali ibn Ridwan described it as a large circular body. He said it looked two to three times larger than Venus. He also noted the sky shone because of its light. In China, the Song dynasty official history recorded the star appearing on May 1, 1006. The Chinese astrologer Zhou Keming told the emperor the star was yellow and auspicious.

Historical records provide many specific details about the sighting. Monks at the Abbey of Saint Gall in Switzerland provided independent data. They recorded the star's magnitude and its location in the sky. In Iran, Ibn Sina observed the star from the northeast. Some reports even claim the star was bright enough to cast shadows on Earth. It was also seen during daytime hours for a period of time. Some researchers think the star might have been seen as early as April 17. This was based on observations discovered from Yemen.

Modern science has finally located the physical remains of the explosion. In 1965, Doug Milne and Frank Gardner used a radio telescope to find a connection. They linked the event to a known radio source called PKS 1459−41. This remnant is a circular shell near the star Beta Lupi. The remnant, known as SNR G327.6+14.6, has a diameter of about 20 parsecs. Scientists have detected X-ray and optical emissions from this shell. In 2010, the H.E.S.S. observatory also detected very-high-energy gamma-ray emissions.

Even though the star was very far away, it left a trace on our planet. Type Ia supernovae can release significant amounts of gamma-ray flux. While SN 1006 was too far to cause major damage, it still left a signal. This signal can be found in nitrate deposits in Antarctic ice. Some researchers also look at North American petroglyphs for clues. These rock carvings in Arizona and New Mexico might depict the star. However, some researchers remain skeptical about these interpretations.