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"Hubble Science"

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"Gravitational Lensing: Nature's Boost"

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As Hubble looks out into these fields of 
galaxies, we sometimes see clusters of  

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galaxies; these are galaxies that are held 
nearby each other by their mutual gravity.  

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These clusters are massive conglomerations. 
There's so much mass that they have an actual  

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observable impact on space-time itself. Einstein 
predicted that mass distorts space, but we didn't  

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realize we could actually see the effects of 
that. But with Hubble, we have been able to see  

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distortions in space around clusters of 
galaxies. The way we see that is when light  

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from a background galaxy travels through that 
cluster of galaxies or around it, due to this  

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gravitational lensing effect. The lensing also 
magnifies that background galaxy. So if we look  

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in some of these distorted arcs, we can see more 
detail than we would ever have been able to see  

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without gravitational lensing, nature's boost. So 
Hubble has been used in an unexpected way for us,  

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to look at nature's magnifying glasses, these 
gravitational lenses, and using those to tell  

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us about much more distant galaxies in detail 
we could never have seen without the lensing,  

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and also to tell us how dark matter 
is distributed in those clusters;  

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because it turns out that most of the mass that's 
distorting space and these clusters of galaxies  

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is made of this unseen dark matter, not the 
visible stars in the galaxies, and we can't  

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see the dark matter. But by seeing how this 
background light is distorted, we can kind of  

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map out where that dark matter is through this 
effect we call gravitational lensing. So we're  

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learning a lot about dark matter, this mystery 
of matter we don't really know what it is, but  

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we know where it is in these clusters because of 
this innovative use of the Hubble Space Telescope.

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