By the early 1920s Sirius B was poised to play another major role in the revolutions that transformed physics and astrophysics during the 20th century. The story begins in 1907 when Albert Einstein was still working as a clerk at the Patent Office in Bern, Switzerland. Just two years earlier he had astonished the world with five earth-shaking papers, including his Theory of Special Relativity that treated uniform relative motions. In 1907 he was taking his first steps towards developing a General Theory of Relativity, which involved gravitation and accelerated motions, when he published a paper that introduced his equivalence principle and first predicted that light emitted from a massive object would appear to be redshifted when viewed by a distant external observer. Four years later in 1911, Einstein—who by then had become a professor at the Karl-Ferdinand University in Prague—published a second paper in Annalen der Physik whose title in English is On the Influence of Gravitation on the Propagation of Light. Not satisfied with his earlier treatment of these subjects, Einstein reconsidered the consequences of his 1907 discussion of the equivalence principle. The equivalence principle, which was the genesis of his General Theory of Relativity, states that the influence of accelerated motion on a body, in the absence of a gravitational field, is effectively no different than the influence of a gravitational field on an unaccelerated body. This is why a freely falling body in a gravitational field experiences weight-lessness. A consequence of the equivalence between gravitational acceleration and accelerated motion is that the mass used in Newton’s law of universal gravitation, and the mass employed in Newton’s second law of motion (Chapter 3) must refer to the same quantity.
KeywordsGravitational Field White Dwarf Spectral Type Equivalence Principle Hydrogen Line
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