Year of the Comet
Comet C/2011 L4 (PANSTARRS)

PANSTARRS information

Comet C/2012 S1 (ISON)

ISON information

Ask Astro

Published: August 28, 2012
rogue-black-hole
We have no direct observational evidence that black holes exist. We only have been able to measure the mass enclosed in a specific area. For a handful of cases, there are no viable explanations for what objects could be so dense except a black hole. From the handful of galaxies where we infer a black hole, we then make the leap that these other galaxies we have measured contain black holes as well. Because nearly every galaxy that scientists have studied in fine detail requires a central black hole, we infer that the remaining hundreds of billions of galaxies also contain one.

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