History of supernova observation

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The known history of supernova observation goes back to 185 CE, when supernova SN 185 appeared, the oldest appearance of a supernova recorded by humankind. Several additional supernovae within the Milky Way galaxy have been recorded since that time, with SN 1604 being the last supernova to be observed.^[1]

Since the development of the telescope, the field of supernova discovery has expanded to other galaxies. These occurrences provide important information on the distances of galaxies. Successful models of supernova behavior have also been developed, and the role of supernova in the star formation process is now increasingly understood.

Contents 1 Early history 2 Telescope observation 3 Recent results 4 Future 5 See also 6 References 7 External links

[edit] Early history

In 185 CE, Chinese astronomers recorded the appearance of a bright star in the sky, and observed that it took about eight months to fade from the sky. It was observed to sparkle like a star and did not move across the heavens like a comet. These observations are consistent with the appearance of a supernova, and this is believed to be the oldest recorded by humankind. SN 185 may also have been recorded in Roman literature.^[2] The gaseous shell RCW 86 is suspected as being the remnant of this event, and recent X-ray studies show a good match for the expected age.^[3]

In 393 CE, the Chinese recorded the appearance of another "guest star", SN 393, in the modern constellation of Scorpius.^[4] Additional unconfirmed supernovae events may have been observed in 369 CE, 386 CE, 437 CE, 827 CE and 902 CE.^[1] However these have not yet been associated with a supernova remnant, and so they remain only candidates. Over a span of about 2,000 years, Chinese astronomers recorded a total of twenty such candidate events, including later explosions noted by Islamic, European and possibly Indian and other observers.^[1][5]

The supernova SN 1006 appeared in the southern constellation of Lupus during the year 1006 CE. This was the brightest recorded star ever to appear in the night sky, and its presence was noted in China, Egypt, Iraq, Italy, Japan and Switzerland. It may also have been noted in France, Syria and North America. Egyptian physician and astrologer Ali bin Ridwan gave the brightness of this star as one-quarter the brightness of the Moon. Modern astronomers have discovered the faint remnant of this explosion and determined that it was only 7,100 light-years from the Earth.^[6]

Supernova SN 1054 was another widely-observed event, with Arab, Chinese and Japanese astronomers recording the star's appearance in 1054 CE It may also have been recorded by the Anasazi as a petroglyph.^[7] This explosion appeared in the constellation of Taurus, where it produced the Crab Nebula remnant. At its peak, the luminosity of SN 1054 may have been four times as bright as Venus, and it remained visible for 23 days.^[8]

There are fewer records of supernova SN 1181, which occurred in the constellation Cassiopeia just over a century after SN 1054. It was noted by Chinese and Japanese astronomers, however. The pulsar 3C58 may be the stellar relic from this event.^[9]

The Danish astronomer Tycho Brahe was noted for his careful observations of the night sky from his observatory on the island of Hven. In 1572 he noted the appearance of a new star, also in the constellation Cassiopeia. Later called SN 1572, this supernova was associated with a remnant during the 1960s.^[10]

A common belief in Europe during this period was the Aristotelian idea that the world beyond the Moon and planets was immutable. So observers argued that the phenomenon was something in the Earth's atmosphere. However Tycho noted that the object remained stationary from night to night—never changing its parallax—so it must lie far away.^[11] He published his observations in the small book De Stella Nova (Latin for "concerning the new star") in 1573. It is from the title of this book that the modern word nova for cataclysmic variable stars is derived.^[12]

The last supernova to be seen in the Milky Way galaxy was SN 1604, which was observed October 9, 1604. Several people noted the sudden appearance of this star, but it was Johannes Kepler who became noted for his systematic study of the object. He published his observations in the work De Stella nova in pede Serpentarii.^[13]

Galileo, like Tycho before him, tried in vain to measure the parallax of this new star, and then argued against the Aristotelian view of an immutable heavens.^[14] The remnant of this supernova was identified in 1941 at the Mt. Wilson observatory.^[15]

[edit] Telescope observation

The true nature of the supernova remained obscure for some time. Observers slowly came to recognize a class of stars that undergo long-term periodic fluctuations in luminosity. Both John Russell Hind in 1848 and Norman Pogson in 1863 had charted stars that underwent sudden changes in brightness. However these received little attention from the astronomical community. In 1866, however, William Higgins made the first spectroscopic observations of a nova, discovering lines of hydrogen in the unusual spectrum of the recurrent nova T Coronae Borealis.^[16] Higgins proposed a cataclysmic explosion as the underlying mechanism, and his efforts drew interest from other astronomers.^[17]

In 1885, a nova-like outburst was observed in the direction of the Andromeda galaxy by Ernst Hartwig in Estonia. S Andromedae increased to 6th magnitude, outshining the entire nucleus of the galaxy, then faded in a manner much like a nova. However, in 1917, George W. Ritchey measured the distance to the Andromeda galaxy and discovered it lay much further than had previously been thought. This meant that S Andromedae, which did not just lie along the line of sight to the galaxy but had actually resided in the nucleus, released a much greater amount of energy than was typical for a nova.^[18]

Early work on this new category of nova was performed during the 1930s by Walter Baade and Fritz Zwicky at Mount Wilson Observatory.^[19] They identified S Andromedae, what they considered a typical supernova, as an explosive event that released radiation approximately equal to the Sun's total energy output for 10⁷ years. They decided to call this new class of cataclysmic variables super-novae, and postulated that the energy was generated by the gravitational collapse of ordinary stars into neutron stars.^[20]

Although supernova are relatively rare events, occurring on average about once a century in the Milky Way, observations of distant galaxies allowed supernovae to be discovered and examined more frequently. The first spectral classification of these distant supernova was performed by Rudolph Minkowski in 1941. He categorized them into two types, based on whether or not lines of the element hydrogen appeared in the supernova spectrum.^[21] Zwicky later proposed additional types III, IV and V, although these are no longer used and now appear to be associated with single peculiar supernova types. Further sub-division of the spectra categories resulted in the modern supernova classification scheme.^[22]

In the aftermath of the Second World War, Fred Hoyle worked on the problem of how the various observed elements in the universe were produced. In 1946 he proposed that a massive star could generate the necessary thermonuclear reactions, and the nuclear reactions of heavy elements were responsible for the removal of energy necessary for a gravitational collapse to occur. The collapsing star became rotationally unstable, and produced an explosive expulsion of elements that were distributed into interstellar space.^[23] The concept that rapid nuclear fusion was the source of energy for a supernova explosion was developed by Hoyle and William Fowler during the 1960s.^[24]

[edit] Recent results

The modern standard model for Type Ia supernovae explosions is based on the proposal by Whelan and Iben in 1973, and are based on a mass-transfer scenario to a degenerate companion star.^[25] In particular, the light curve of SN 1972e in NGC 5253, which was observed for more than a year, was followed long enough to discover that after its broad "hump" in brightness, the supernova faded at a nearly constant rate of about 0.01 magnitudes per day. Translated to another system of units, this is nearly the same as the decay rate of cobalt-56 (⁵⁶Co), whose half-life is 77 days. The degenerate explosion model predicts the production of about a solar mass of nickel-56 (⁵⁶Ni) by the exploding star. The ⁵⁶Ni decays with a half-life of 6.8 days to ⁵⁶Co, and the decay of the nickel and cobalt provides the energy radiated away by the supernova late in its history. The agreement in both total energy production and the fade rate between the theoretical models and the observations of 1972e led to rapid acceptance of the degenerate-explosion model.^[26]

Through observation of the light curves of many Type Ia supernovae, it was discovered that they appear to have a common peak luminosity.^[27] By measuring the luminosity of these events, the distance to their host galaxy can be estimated with good accuracy. Thus this category of supernovae has become highly useful as a standard candle for measuring cosmic distances. In 1998, the International Supernova Cosmology Project discovered that the most distant Type Ia supernovae appeared dimmer than expected. This has provided evidence that the expansion of the universe may be accelerating.^[28][29]

Although no supernova has been observed in the Milky Way since 1604, it appears that a supernova exploded in the constellation Cassiopeia about 300 years ago, around the year 1667 or 1680. The remnant of this explosion, Cassiopeia A - is heavily obscured by interstellar dust, which is possibly why it did not make a notable appearance. However it can be observed in other parts of the spectrum, and it is the currently the brightest radio source beyond our solar system.^[30]

In 1987, Supernova 1987A in the Large Magellanic Cloud was observed within hours of its start. The relative proximity of this supernovae has allowed detailed observation, and it provided the first opportunity for modern theories of supernova formation to be tested against observations.

The "Champagne Supernova" was discovered in a forming galaxy in 2003. The appearance of this supernova was studied in "real-time", and it has posed several major physical questions as it seems more massive than the Chandrasekhar limit would allow.^[31]

Astronomers discovered that supernova 2006gy had set a new record for intrinsic luminosity, being about 3 times brighter than any previously recorded supernova burst. Although this had characteristics of a type Ia supernova, Hydrogen was found in the spectrum. However it occurred in a galaxy consisting primarily of older, evolved stars, so it is thought unlikely to be a type II explosion. A possible explanation is that this event was caused by the merger of two stars, at least one of which may have been a white dwarf.^[32]

[edit] Future

The estimated rate of supernova production in a galaxy the size of the Milky Way is about one every 50 years. This is much higher than the actual observed rate, implying that a portion of these events have been obscured from the Earth by interstellar dust. However new instruments that can observe across a wide range of the spectrum, as well as the deployment of neutrino detectors, mean that the next such event will almost certainly be detected.^[33]

[edit] See also

• History of astronomy

[edit] References

[edit] External links

• Hecht, Jeff. "Enigmatic object baffles supernova team", NewScientist.com, June 19, 2006. Retrieved on 2006-12-01.