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Issue 5.18

The Astrophysics Spectator

November 18, 2008

With this issue, I add some better organization to the web site.  Most of the pages on degenerate objects—giant gaseous planets, brown dwarfs, degenerate (white) dwarfs, and neutron stars—had been placed under the “Stars” topical path, and the remaining pages had been placed under the “Planets” topical path.  With this issue, the pages on degenerate objects that appeared under the “Stars” topical path now appear under the new “Degenerate Objects” topical path.

Five types of long-lived astronomical object can be defined by the physics found within an object: the fusion-powered star, the small planet, the electron-degenerate object, the neutrons star, and the black hole.  The fusion-powered star is held up by the thermal pressure exerted by electrons, ions, and light.  The small planet—a planet smaller than Saturn—is held up by the pressure exerted by atoms.  The black hole is a pure gravitational field.  The remaining two types of astronomical object, the electron-degenerate object and the neutron star, are similar in being held up by degeneracy pressure, and they are distinct in the particle exerting this pressure.

The electron-degenerate object—which can be a giant gaseous planet, a brown dwarf, or a degenerate dwarf—is held up by electrons; despite ranging dramatically in mass and following radically different evolutionary paths, the different types of electron-degenerate object  are similar in structure.  The second type of degenerate object, the neutron star, is held up by neutrons and protons.  It is much smaller than an electron-degenerate object; this compactness makes the physics around a neutron star much more exotic than around an electron-degenerate object.

  Degenerate objects are remnants, no longer generating energy, no longer shrinking in size.  They are quite unlike the fusion-powered stars.  For this reason, I have given them their own topical path.

Next Update:  This is the last issue of the web site for the year, as I take the holiday season off.  I will resume updating the site sometime around the 14th of January, 2009.  I wish my readers a wonderful Thanksgiving, a merry Christmas, and a happy New Year.

Jim Brainerd

Degenerate Objects

Introduction.  Degeneracy pressure—the pressure caused by the Pauli exclusion principle of quantum mechanics—is manifested by four types of astronomical object: the giant gaseous planet, the brown dwarf, the degenerate dwarf, and the neutron star.  The first-three objects constitute the subclass of degenerate objects that are supported by electron degeneracy pressure.  The neutron star is the subclass of degenerate objects supported by neutron and proton degeneracy pressure.  The degenerate dwarf and the neutron star are two of the three endpoints of stellar evolution (the third endpoint is the black hole).  Binary star systems containing a degenerate object are the most brilliant systems in the Galaxy.  (continue)

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