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Sean Carroll

Did LIGO Detect Dark Matter?

10 Mar 2016, 20:57 UTC
Did LIGO Detect Dark Matter?
(200 words excerpt, click title or image to see full post)

It has often been said, including by me, that one of the most intriguing aspects of dark matter is that provides us with the best current evidence for physics beyond the Core Theory (general relativity plus the Standard Model of particle physics). The basis of that claim is that we have good evidence from at least two fronts — Big Bang nucleosynthesis, and perturbations in the cosmic microwave background — that the total density of matter in the universe is much greater than the density of “ordinary” matter like we find in the Standard Model.
There is one important loophole to this idea. The Core Theory includes not only the Standard Model, but also gravity. Gravitons themselves can’t be the dark matter — they’re massless particles, moving at the speed of light, while we know from its effects on galaxies that dark matter is “cold” (moving slowly compared to light). But there are massive, slowly-moving objects that are made of “pure gravity,” namely black holes. Could black holes be the dark matter?
It depends. The constraints from nucleosynthesis, for example, imply that the dark matter was not made of ordinary particles by the time the universe was a minute old. ...

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