Dark Matter No More Than 40% Black Holes

If dark matter consists of a plethora of primordial black holes, then their gravitational lensing – magnifying and brightening distant objects – should be detectable. Physicists analyzed 740 known supernovas to find the handful that should have been magnified and brightened by black holes, and found none. This puts a strong upper limit, 40, on the percent of dark matter that can consist of black holes, and suggests that none of it is.

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