CH11 - Chapter 11: Neutron Stars and Black Holes Stellar...

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Neutron Stars and Black Holes Chapter 11:
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Stellar Remnants (Image Source: Harvard CFA)
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What's Left After a Star Dies? Three final states for stars: White Dwarfs: M < 10 M Neutron Stars: 10 < M < 25 M Black Holes: M > 25 M Which one depends on a star's mass: more massive stars have stronger gravity pulling them together, and therefore have more compact remnants. mass of progenitor star
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White Dwarfs Electron degenerate stellar cores: star is supported against gravity by pressure due to Pauli exclusion principle in electrons. Almost entirely carbon: cool core of star condenses into solid material much like diamond (10 billion trillion trillion carats. ..) (Image: Harvard CFA)
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Sirius B White dwarf companion to Sirius (brightest star in sky). (Image: Lick Observatory)
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Sirius B White dwarf companion to Sirius (brightest star in sky). (Image: Chandra Space Telescope)
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Sirius B Discovered 1892: very hot (and therefore young) white dwarf. T = 29,000 K Ptolemy, in 140 C.E., describes Sirius as “fiery red”. Also Cicero, Horace, Homer, Seneca. Al Sufi (10th Century) does not classify Sirius as red. Sirius is white today.
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Sirius B Discovered 1892: very hot (and therefore young) white dwarf. T = 29,000 K Ptolemy, in 140 C.E., describes Sirius as “fiery red”. Also Cicero, Horace, Homer, Seneca. Al Sufi (10th Century) does not classify Sirius as red. Sirius is white today. Could Sirius B have been a red giant 2000 years ago? Unlikely from our understanding of stellar evolution. Other explanation might be a transient event due to mass transfer from Sirius A.
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Sirius B First object to display gravitational redshift of spectral lines: test of Einstein's theory of General Relativity
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Typical White Dwarf Size Sirius B: 61,000 times as dense as sun!
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White Dwarf Numbers Mass around ½ – 1.4 solar mass Radius: 0.01 solar radii (10,000 km) Density: 105 – 109 g / cm3 (water 1 g / cm3) White dwarfs with larger masses have smaller radii! 1 cc = 10 tons!
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The Chandrasekhar Limit Subrahmanyan Chandrasekhar Born 1910, Lahore (part of India at the time, now in Pakistan) Started college at age 15, and moved to England to study in 1930. Derived Chandrasekhar Limit on boat to England. Gave a talk at Royal Astronomical Society in 1935. Ridiculed by Eddington, the work was not widely accepted. Moved to University of Chicago in 1937 Nobel Prize, 1983
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Sirius B discovered 1892, but electron degeneracy was not understood until after the development of quantum mechanics (1920's). Key fact: The larger the mass of a white dwarf, the smaller the radius. Chandrasekhar Limit:
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CH11 - Chapter 11: Neutron Stars and Black Holes Stellar...

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