2
$\begingroup$

When LIGO said one merging black hole was thirty or so solar masses, the other twenty, and that they were one billion light years away; how do they know that?

$\endgroup$

marked as duplicate by Rob Jeffries, John Rennie, Jon Custer, AccidentalFourierTransform, stafusa Apr 9 '18 at 7:33

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.