Astronomers Have a New Way to Measure the Expansion of the Universe - by BrianKoberlein
The other approach looks at distant supernovae. One type of supernova known as Type Ia has a fairly uniform maximum brightness. So if you know the distance to a Type Ia supernova, you can compare its apparent brightness to its actual brightness, and calculate cosmic expansion. This relies on knowing the distance to the supernova’s galaxy, which relies on a complex set of distance calculations known as the cosmic distance ladder. This approach gives a Hubble value of about 71 – 75 /Mpc.
The technique of gravitational lensing relies on the presence of a large cluster of matter between the observer and the object to magnify light coming from that object. Credit: NASA The supernova was first observed in 2014. It was nicknamed Refsdal after Norwegian astronomer Sjur Refsdal, who first proposed the idea of time-delayed supernovae in 1964. The Refsdal supernova happened to be located in a gravitationally lensed galaxy. When astronomers realized this, they used computer models to predict when the supernova would appear again. They estimated it should appear again sometime in 2015-2017, and sure enough in 2015 it appeared again.
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