Several news articles—“Scientists Chart Dark Matter Halo That Binds Milky Way” (Christian Science Monitor), “Astronomers Map Dark Matter ‘Beach Ball’” (National Public Radio), and “Dark Matter ‘Beach Ball’ Unveiled” (BBC) —cover a January 6 press briefing by David R. Law (UCLA) at the 215th American Astronomical Society meeting. The BBC article begins:
It is the first definitive measure of the scope of the dark matter that makes up the majority of galaxies’ masses.
The shape of this “dark matter halo” was inferred from the path of debris left behind as the Sagittarius dwarf galaxy slowly orbits the Milky Way.
National Public Radio also has a background blog about dark matter: “Dark Matter: ‘What Is Essential Is Invisible.’”
The comprehensive (and interdisciplinary) number for dark matter is 523.1126 Dark matter; an example of a work classed there is In Search of Dark Matter.
The comprehensive (and interdisciplinary) number for the Milky Way is 523.113 Milky Way; an example of a work classed there is The Milky Way.
Where should a work about dark matter as part of the Milky Way be classed? The number for dark matter (523.1126) is a subdivision of 523.112 Galaxies. At 523.112 is the see reference: “For Milky Way, see 523.113.” That see reference acknowledges that the Milky Way is a galaxy and therefore logically belongs in a subdivision of 523.112—but specifies that works on that particular galaxy are classed in 523.113 Milky Way. General works on interstellar matter of the Milky Way are classed in 523.1135 Interstellar matter; however, the entry for 523.1135 has the see reference: “For dark matter, see 523.1126.” Consequently, works on dark matter as part of the Milky Way are classed with other dark matter in 523.1126 Dark matter, e.g., Dark Matter in the Milky Way.
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