The image above shows the extent of the supernova remnant designated SN 1006. In this X-ray image taken with the Chandra space telescope, multi-million degree gas is shown as red and green, while extremely high-energy electrons are shown as blue. While it is not known what type of star created this remnant, it is believed that the progenitor was most likely a white dwarf that exploded when it exceeded the Chandrasekhar limit after cannibalizing a nearby companion star.
When this “guest star” appeared in the constellation Lupus between April 17th and May 1st in the year 1006 AD, observers that were spread over much of the known world, including China, Japan, Egypt, modern-day Iraq, and Europe described it as being at least sixteen times as bright as Venus. Most reports from this time also mention the fact that the “guest star” was clearly visible during daytime, and based on these reports, modern distance estimates put the remnant at about 7,200 light years away from Earth.
Although SN 1006 was known from historical records, the actual remnant was not discovered until 1965, when astronomers Frank Gardner and Doug Milne used the Parkes Radio Telescope to investigate a known radio source designated PKS 1459-41 that was located close to the star Beta Lupi. As it turned out, their investigation revealed a circular shell with a diameter of 30 minutes of arc, which later proved to be the remnant of the supernova that so many observers reported in the year 1006 AD.
Follow-up observations showed both hard X-ray and optical emissions from the remnant, and further examinations made in 2010 with the H.E.S.S. gamma-ray observatory revealed evidence of extremely energetic gamma ray emissions from the remnant. However, despite a diligent search, no evidence or trace of an associated black hole or neutron star has been found either in, or close to SN 1006.
As a practical matter, this is to be expected from a Type Ia supernova, in which the progenitor star is completely destroyed. In fact, since a further follow-up study in 2012 found no evidence of the presence of surviving companion giant or sub giant stars, most investigators now believe that SN 1006’s progenitor was actually a pair of white dwarfs that exploded when they merged or collided.
SN 1006 in History
Based on historical records and reports, it is likely that SN 1006 was the brightest supernova event ever recorded. In fact, the ancient Egyptian astronomer Ali ibn Ridwan wrote in a comment on Ptolemy’s Tetrabiblos that “[the] spectacle was a large circular body, 2½ to 3 times as large as Venus. The sky was shining because of its light. The intensity of its light was a little more than a quarter that of Moon light”. As all other observers, Ali ibn Ridwan made a particular point of the fact that the “guest star” appeared, and remained low on the southern horizon, which some contemporary astrologers took as a sign of impending famine and plague. Meanwhile, Persian scientist Ibn Sina (980 to 1037 AD) gives an interesting account of a transient celestial object that started out greenish yellow in color, and later turned whitish and twinkled wildly at its peak brightness, before throwing out sparks and ultimately vanishing from sight.
Nonetheless, in Europe, the most northerly observation of the supernova was made by several monks of the Abbey of Saint Gall in Switzerland, which is located on latitude 47.5 degrees North. The monks noted the event thus- “[in] a wonderful manner this was sometimes contracted, sometimes diffused, and moreover sometimes extinguished… It was seen likewise for three months in the inmost limits of the south, beyond all the constellations which are seen in the sky”. To some modern investigators, this particular report represents probable evidence that the event was indeed a Type Ia supernova that was bright enough for its light to have cast shadows in the daytime- as is mentioned in several historical accounts.
In one Chinese record, known as the Songshi, the “guest star” was reported to be a little south of the (ancient Chinese) constellation Di, east of the modern constellation Lupus, and roughly one degree to the west of the constellation Centaurus. Chinese records also indicate that the supernova appeared in two distinct phases; the first being a three-month period during which the “guest star” shone at its brightest, after which it dimmed considerably. The exact start of the second phase is not clear, but it seemed to have returned for a period of about eighteen months after the first, bright phase.
Being as bright as SN 1006 was, it is almost inconceivable that the native North American peoples would not also have observed it, given their known stargazing skills. One particular tribe, the Hohokam of modern-day Arizona, left a petroglyph that may or may not show a representation of the supernova. However, since not much is known about how most native North American peoples viewed the Universe, or just how important celestial events such as “guest stars” were to them, many researchers are rather skeptical of the notion that the petroglyph in the White Tank Mountain Regional Park represents SN 1006, or for that matter, any other major celestial event.
Did SN 1006 Affect Earth in Any Way?
Most researchers agree that supernova events that occur within about 1 kiloparsec (3,200 light years) of Earth can have a significant, if not necessarily a fatal impact on the amounts of gamma-ray radiation that reaches Earth. The greatest impact would be on the ozone layer, which might produce unpredictable affects on plant and animal life, as well as on the global climate.
However, at its distance of about 7,200 light years, SN 1006 did not seem to have affected Earth in meaningful ways, if at all, although some evidence of the fact that at least some of its gamma ray emissions have reached Earth have been found in nitrate deposits in Antarctic ice core samples.