Nova (temporary brightness of a white dwarf star):
A nova (plural novae or novas) is a cataclysmic nuclear explosion in a white dwarf, which causes a sudden brightening of the star. Novae are not to be confused with other brightening phenomena such as supernovae or luminous red novae. A nova is caused by the accretion of hydrogen onto the surface of the star, which ignites and starts nuclear fusion in a runaway manner. Novae are thought to occur on the surface of a white dwarf in a binary system. If the two stars are close enough, material can be pulled from the companion star's surface onto the white dwarf.Supernova (death of a star):
A supernova is a stellar explosion that briefly outshines an entire galaxy, radiating as much energy as the Sun is expected to emit over its entire life span, before fading from view over several weeks or months.
The extremely luminous burst of radiation expels much or all of a star's material at a velocity of up to 30,000 km/s (10% of the speed of light), driving a shock wave into the surrounding interstellar medium. This shock wave sweeps up an expanding shell of gas and dust called a supernova remnant. A great proportion of primary cosmic rays comes from supernovae.
Supernovae are more energetic than a nova. Nova means "new" in Latin, referring to what appears to be a very bright new star shining in the celestial sphere; the prefix "super-" distinguishes supernovae from ordinary novae which are far less luminous. The word supernova was coined by Walter Baade and Fritz Zwicky in 1931.
Supernovae can be triggered in one of two ways: by the sudden re-ignition of nuclear fusion in a degenerate star; or by the gravitational collapse of the core of a massive star.
A degenerate white dwarf may accumulate sufficient material from a companion, either through accretion or via a merger, to raise its core temperature, ignite carbon fusion, and trigger runaway nuclear fusion, completely disrupting the star. The core of a massive star may undergo sudden gravitational collapse, releasing gravitational potential energy that can create a supernova explosion.
Although no supernova has been observed in the Milky Way since Kepler's Star of 1604 (SN 1604), supernova remnants indicate that on average the event occurs about three times every century in the Milky Way. They play a significant role in enriching the interstellar medium with higher mass elements. Furthermore, the expanding shock waves from supernova explosions can trigger the formation of new stars.Chapter 1: Exploding Stars
Supernova: a massive star, much more massive than itself, runaway fusion, hydrogen --> helium --> carbon; collapses in on itself; becomes a neutron star. Inside the interior of the dense, collapsed star, ordinary protons and electrons can no longer co-exist; they fuse and become neutrons. TYPE IIA.
Super-supernova: TYPE 1A. Six times as bright as an ordinary supernova. Again, a white dwarf attracts surrounding matter, becomes 1.4 times as massive as our Sun, and then explodes.
Perlmutter, late 1990s, noted that the universe's expansion was accelerating; unheard of at that time, and not expected. This meant something frightening: our universe is infinite. Announced to the world in 1998. The mass of the known universe was too small to stop the universe from expanding forever.
"Sunsets are red, the sky is blue" -- Rayleigh's Blue Sky Law that every beginning physics student recites.
Chapter 2: Early Einstein
Chapter 3: Prague, 1911
Chapter 4: Euclid's Riddle
p. 59 -- "the happiest thought"
Famous thought experiment: imagined a circle spinning in space -- the center of the circle did not move but its circumference was moving quickly in a circular directions....concluded that the boundary of the disk contracted as it spun...a force acting on the circle at the boundary -- the centrifugal force -- and its action as analogous to that of a gravitational force. But the same contraction that affected the outer circle left the diameter unchanged. Thus Einstein concluded, in a way that surprised even him, the ratio of the circle to the diameter was no longer pi. He deduced that in the presence of a gravitational force (or field), the geometry of space in non-Euclidian.
Chapter 5: Grossman's Notebooks
- concept of a tensor
- increasingly complex mathematics needed to solve the problems of relativity; Grossman, a contemporary student, helped him
- 1913: the visit to Zurich that would change his life forever; Max Planck (1858 - 1947) and Hermann Nernst (1864 - 1941) visited Zurich where Einstein was (ETH); at their insistence he moved to Berlin, center of anti-Semitism at the time
- the Crimean, August 1, 1914
- collaboration with Freundlich
- August 2, 1913: excited; "I am quite convinced that the rays of light get bent."
- also very interested in Freundlich's interest in double stars
- December 7, 1913: the eclipse viewed from the Crimean would prove/disprove whether rays of light bend
- Einstein spends considerable time countering Freundlich's assertion that detection of starlight shifts near the Sun could be done in daytime without a total solar eclipse. Einstein said "no" in no uncertain terms. Author's footnote: this feat is still not possible today. Even during an eclipse, detecting the bending of light requires a complicated procedure.
- July 19, 1914: reach the town of Feodosiya in the Crimea
- [June 28, 1914: Archduke Ferdinand assassinated.]
- a rift develops between Freundlich and Einstein; author suggests it was Einstein's fault
- Einstein reading astronomer Arthur Eddington's work; coincidentally, and unknown at that time, March 1, 1919, Eddington was planning to embark on a trip to to an island off the coast of equatorial Africa to watch an eclipse of the Sun to try to detect the bending of star light to prove Einstein's theory of general relativity
- Riemann attracted to Gottingen where Gauss was teaching
- Gauss assigned Riemann his third choice for a presentation to start Riemann on his road to a position at Gottingen: a whole new theory in geometry requiring the fields of complex numbers and number theory
- Riemann's presentation was a theory that would change the face of both geometry and the physical sciences forever. What was Riemann's groundbreaking idea?
- Riemann decided that the property of a surface that he needed to understand and capture was the notion of a distance (also called a metric). Riemann used a non-flat surface, developed a new formula, and 60 years later, Einstein would use that formula to finally derive the equations of general relativity; a crucial element in Einstein's tensor equation, signifying the metric tensor. The metric tensor would allow Einstein to account for the curvature that the gravitational field imposed upon the space of the universe
- Riemann's idea led to a new theory: differential geometry
- the general approach had implications in the field of topology
- topology is the study of spaces and continuous functions; it deals with questions such as whether a surface is connected or made up of several disconnected components; whether sequences of points converge to a point in the space itself or outside it; and whether it is possible to cover an infinite space with a finite collection of subsets
- equivalences: a cup with a single handle and a doughnut for example
- Reimann died of consumption, at a villa on Lago Maggiore in northern Italy, 1866; age 39
- Einstein: voted into the Prussian Academy in Berlin, 1913, war
- "The race to finish the general theory of relativity is a story of mathematical trial-and-error in solving the great puzzle of matter and gravitation, which Einstein performed at an amazing speed during one incredible month: November, 1915."
- all of his problems would be solved in a whirlwind of mathematical research using Riemannian geometry during November
- a great chapter explaining, almost day-by-day, how Einstein solved the problem
- the story of smuggling Einstein's paper on general relativity to Arthur Eddington in England
- Eddington, born 1882
- fascinated by large numbers; as a youngster memorized the entire 24 x 24 multiplication table
- Dyson and Eddington, near the end of WWI -- set out to prove general relativity; another eclipse, Brazil
- their trip was successful; verified Einstein's equations
- 1919: results were verified by Eddington, but Einstein was not informed
- September 1919: Einstein informed
- it is now clear, that near a massive object, space is non-Euclidean -- it is curved
- the question may then arise: what is the shape of the entire universe, not just hte local neighborhood of a massive object such as a star? But here again, Einstein was way ahead of the crowd
- Einstein had already begun to consider the shape and evolution of the entire universe two years before the big event of the 1919 eclipse
- his work would lead him to the most controversial hypothesis of his life
- in 1917, while manipulating his field equation, Einstein unwittingly opened a Pandora's box
No comments:
Post a Comment