What effect do massive clusters cause that helps map their total mass, including dark matter?
Answer
Bending the light from distant background galaxies
Gravitational lensing is a powerful technique used to measure the total mass contained within a galaxy cluster, which is crucial because much of that mass is unseen dark matter. According to general relativity, any massive object warps the fabric of spacetime around it. When light from extremely distant background galaxies passes near a galaxy cluster on its way to Earth, this warped spacetime causes the light paths to bend. Mapping the degree and pattern of this bending allows scientists to calculate the total gravitational mass distribution of the foreground cluster, thereby accounting for the dark matter component.
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