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The uncertainty of science: New more robust measurements by Australian astronomers has shown that the amount of dark matter in the Milky Way galaxy is about half of what previous measurements had estimated.
Without doubt something is causing the outer stars in galaxies to orbit their galaxies at much greater speeds than they should. The answer that astronomers have posited since the late 1950s is that there is additional unidentified mass, dubbed dark matter, lurking as a halo around each galaxy, pulling on those outer stars and making them move faster.
The problem remains that no one has as yet detected this unidentified dark matter. Moreover, there are enormous uncertainties in the measurements of the motions of stars. This result helps narrow those uncertainties.