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Q & A: dark matter and light bending

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Most recent answer: 04/17/2017
Q:
Two questions. 1) If "black matter" is real, why don't we observe light from stars bending/slowing down at random places on its way to earth? (I'm kind of assuming BM is not uniform throughout the whole universe, but is rather bunched up around stars/ galaxies, correct me if I'm wrong) 2) If black matter holds stars in place, doesn't stellar black holes do that already?
- Luke Langlois (age 15)
Louisiana, U.S.A.
A:

You're right that dark matter should bunch up with our type of matter . Those clumps of matter should cause light to bend, called gravitational lensing. Exactly that effect is observed:  http://cosmology.berkeley.edu/Education/CosmologyEssays/Gravitational_Lensing.html
http://cosmology.berkeley.edu/Education/CosmologyEssays/Gravitational_Lensing.html.
It's much too big to be due to the matter in stars, and thus is one of the pieces of evidence indicating the existence of dark matter.

Stellar black holes do help hold things together via gravity, but there aren't enough of them and they don't have the right distribution in space to account for the gravitational effects of dark matter.

Mike W.

 


(published on 04/17/2017)

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