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Can Time Dilation Near a Black Hole Explain the Orbits of Stars Near the Black Hole?

-- | July 21, 2015

Question: Regarding galaxy rotation. Although the supermassive black hole at the center of a Galaxy probably isn’t strong enough to speed up the rotation of its more distant stars so as to make the velocity curve level, nevertheless the time-dilation effect of such a black hole will make the orbital rotation speeds of the inner stars appear slower than it actually is as seen from the point of view of an observer outside the galaxy in question. Couldn’t this be a more reasonable explanation rather than hypothesizing ‘dark matter’? — Tom

Answer: I don’t think that time dilation will affect the observed speed of stars near a black hole as observed from a point far from the black hole. Time dilation affects what local observers measure, which means that the time measured by an observer at a star near a black hole will see time running slower than the time measured by the far-away observer.

Jeff Mangum

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