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Crab Nebula in Infra-red (Spitzer Space Telescope) |
When last we met, our hero, the intrepid astronomer Yang Weide, had 'prognosticated' for his boss, the Emperor Chih-Ho, the tidings of the arrival and departure the the brilliant 'guest star.' Visible during the day for 23 days, now nearly two years later the star was gone. In his offices at the Imperial Observatory in Kaifeng Yang ponders the various and sundry concerns that administrator-scientists even to this day weigh. The Emperor, he muses, wasn't so generous with his purse this year. The budget is tight and Yang wonders how he'll afford to apprentice his wife's nephew and achieve some peace at home. Yet foremost in his thoughts is: "What are these transient apparitions that so brilliantly pierce our skies both day and night?"
I could be worse employed Than as watcher of the void, Whose part should be to tell What star if any fell. |
Robert Frost |
Over the next 900 years various theories were proposed to explain the these suddenly brilliant suprise stars that visited for a while and faded away.
Tycho Brahe, the man with the golden nose, suggested that these events were just 'new' stars in his pamphlet De Stella Nova (1573).
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A composite image of the Tycho nebula combines infrared and X-ray observations. (Spitzer and Chandra and Calar Alto Observatory (Spain) |
Others theorized that these stars moved closer to earth as they brightened and away as they faded. Collision theories were proposed by
Isaac Newton and others that advocated that various astronomical bodies (comets, planets, etc) colliding with dead stars caused these flares of starlight.
Newton, by the way, also studied the spectra of sunlight through a prism, certainly not the first study of prismatic light, but he did propose a theory of color based on his observations. Science built on this work and by the mid-nineteenth century spectroscopic studies recognized that each element displays distinctive spectra and astronomers were using this tool to investigate the light coming from stars and novae to determine their elemental composition.
William Huggins and William Miller interpreted the bright hydrogen lines in the spectrum of the nova T Coronae Borealis in 1866 as due to an explosion and chemical combustion of hydrogen in the star (Friedjung and Duerbeck 375). Also, William H. Pickering found evidence in the spectra of the bright nova GK Persei (1901) that the collision theories were not valid physical explanations of novae. [A History of Astronomy p363]
Astronomers began to understand that the were significant differences between the various and now many novas observed up to the mid 1880's. In the observations of an event in the Andromeda Nebula it was found that the apparent brightness of that stellar explosion rivaled that of what was then thought of as a nebula. Not only was the nova exceptionally luminous it exhibited a totally different spectra from other novae known at the time. Yet astrophysicists still couldn't explain how such things could happen, let alone how stars generated energy. It wasn't until the publication of a little paper by an unknown 26 year old Swiss Patent Office worker called "Does the Inertia of a Body Depend Upon Its Energy Content?" (1905) that a framework for a solid understanding stellar physics could form.
Einstein's paper provided the first mechanism to explain how stars generate the tremendous amounts of energy they do without consuming their fuel. As a matter of fact, his 4 papers, now called the Annus Mirabilis Papers are pretty much the basis for all the advances of modern physics, from quantum mechanics to stellar evolution. Certainly, over the next 30 years or so, they generated a lot of new theoretical thinking.
Astronomers saw for the first time that novae were not truly 'new' stars—in terms of stellar genesis—in 1918 with the nova V603 Aquilae. Photographic plates from 30 years earlier showed that there was, indeed, a star at the location of the event. In a few years later, during the 20's, better photographic techniques and telescopes, allowed astronomers to discover that what they had thought of as gaseous nebulae in the Milky Way were, in fact, distant galaxies. This implied that the nova discovered in those galaxies must be releasing tremendous amounts of energy to be so luminous.
It was also in 1920 that the first proposition that star's generated energy via thermonuclear fusion was made by Arthur Stanley Eddington. Eddington, an early supporter of Einstein, proved to be the beginning of our modern understanding of the physics of starlight.
Most of the pieces were in place for a comprehensive understanding of the physics of stars was in place by the 1930's. The final piece was discovered in 1932 by James Chadwick when he discovered, experimentally, the existence of the neutron. Now all that was needed was someone to put it all together.
It was Fritz Zwicky, an incredibly imaginative physicist and so-called 'father of the modern jet engine', and Walter Baade that were the scientists who, essentially, put it all together. Zwicky and Baade proposed that the extra-galactic nova that astronomers had witnessed were gravitationally driven stars that had run out of their nuclear fuel (hydrogen, helium,...). They postulated that the collapse lead to a state of neutron degeneracy or neutron star and the generation of cosmic rays. They called these events supernovae.
References
A History of Astronomy p363.
The Modern Physical and Mathematical Sciences p520.
Bibliography
Baade, W.; Zwicky, F. (1934), On Super-Novae", Proceedings of the National Academy of Sciences 20: 254–259, doi:10.1073/pnas.20.5.254
Baade, W.; Zwicky, F. (1934), "Cosmic Rays from Super-novae", Proceedings of the National Academy of Science 20 (5): 259–263, doi:10.1073/pnas.20.5.259
Fritz Zwicky's Extraordinary Vision, retrieved on 16 July 2007, an extract from Soter, S. (2000), Cosmic Horizons: Astronomy at the Cutting Edge, New Press
Thanks for reading!