History of Supernova Observation - Telescope Observation

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. Finally, in 1866, English astronomer William Huggins made the first spectroscopic observations of a nova, discovering lines of hydrogen in the unusual spectrum of the recurrent nova T Coronae Borealis. Huggins proposed a cataclysmic explosion as the underlying mechanism, and his efforts drew interest from other astronomers.

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. In 1917, George W. Ritchey measured the distance to the Andromeda galaxy and discovered it lay much farther 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.

Early work on this new category of nova was performed during the 1930s by Walter Baade and Fritz Zwicky at Mount Wilson Observatory. 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. The name super-novae was first used in a 1931 lecture at Caltech by Zwicky, then used publicly in 1933 at a meeting of the American Physical Society. By 1938, the hyphen had been lost and the modern name was in use.

Although supernovae are relatively rare events, occurring on average about once every 50 years in the Milky Way, observations of distant galaxies allowed supernovae to be discovered and examined more frequently. The first supernova detection patrol was begun by Zwicky in 1933. He was joined by Josef J. Johnson from Caltech in 1936. Using a 45-cm Schmidt telescope at Palomar observatory, they discovered twelve new supernovae within three years by comparing new photographic plates to reference images of extragalactic regions.

In 1938, Walter Baade became the first astronomer to identify a nebula as a supernova remnant when he suggested that the Crab Nebula was the remains of SN 1054. He noted that, while it had the appearance of a planetary nebula, the measured velocity of expansion was much too large to belong to that classification. During the same year, Baade first proposed the use of the Type Ia supernova as a secondary distance indicator in 1938. Later, the work of Allan Sandage and Gustav Tammann helped refine the process so that Type Ia supernovae became a type of standard candle for measuring large distances across the cosmos.

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. 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.

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. 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.

The first computer-controlled search for supernovae was begun in the 1960s at Northwestern University. They built a 24-inch telescope at Corralitos Observatory in New Mexico that could be repositioned under computer control. The telescope displayed a new galaxy each minute, with observers checking the view on a television screen. By this means, they discovered 14 supernovae over a period of two years.

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