when was the last component mentioned above studied?
1884
Dark matter
1884
what is the galaxy? It is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. where does the name come from? It is derived from the Greek word literally "milky".
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Dark matter [SEP] Early history
The hypothesis of dark matter has an elaborate history. In a talk given in 1884, Lord Kelvin estimated the number of dark bodies in the Milky Way from the observed velocity dispersion of the stars orbiting around the center of the galaxy. By using these measurements, he estimated the mass of the galaxy, which he determined is different from the mass of visible stars. Lord Kelvin thus concluded "many of our stars, perhaps a great majority of them, may be dark bodies". In 1906 Henri Poincaré in "The Milky Way and Theory of Gases" used "dark matter", or "matière obscure" in French, in discussing Kelvin's work.