Tag: rotation Curve

Dark Matter in a Galaxy Cluster

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We know that galaxies like our Milky Way are far more massive than we can see.  The dark matter in the Milky Way makes up 90% of it’s total mass.  Another way of saying this is the Mass to Light ratio, comparing the total mass inferred by the rotation speed of the galaxy to the total mass of stars in the galaxy.  This ratio, M/L, for the Milky Way, is about 10.  But for a galaxy cluster, the M/L ratio is more like 100.  Galaxy clusters are not just dense collections of stars and massive galaxies, they are also immense...

Dark Matter Domination

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Dark matter is everywhere.  There is way more of it in the universe than the matter we are made of and interact with.  Yet for the sheer amount of it, we have no way of determining what exactly it is.  It’s as if we didn’t know what air was, and even though we could see it and breathe it, we couldn’t measure it.  The most tantalizing part about dark matter is that we can see the gravitational effect it has, and so we can determine how much of it there has to be.  Some places in the universe have more dark matter than...