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How You Can Weigh Black Holes

Messier 81 (also known as NGC 3031 or Bode’s Galaxy) is a barred spiral galaxy in the constellation Ursa Major 11.4 million light years away. The pitch angle of its spiral arms is 13.4°, which correlates with the black hole at its centre being 67.6 million times more massive than our Sun. Credit: © Ken Crawford http://www.imagingdeepsky.com/Galaxies/
M81/M81.htm

Messier 81 (also known as NGC 3031 or Bode’s Galaxy) is a barred spiral galaxy in the constellation Ursa Major 11.4 million light years away. The pitch angle of its spiral arms is 13.4°, which correlates with the black hole at its centre being 67.6 million times more massive than our Sun. Credit: © Ken Crawford http://www.imagingdeepsky.com/Galaxies/ M81/M81.htm

By Ben Davis

The largest invisible monsters in our universe are hidden at the centres of galaxies, and we can predict how massive they are by the shape of spiral arms in their host galaxies. Here’s how you can take part in a global “citizen science” census of black holes.

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