Astronomers using National Science Foundation radio telescopes have demonstrated how a combination of gravitational-wave and radio observations, along with theoretical modeling, can turn the mergers of pairs of neutron stars into a "cosmic ruler" capable of measuring the expansion of the universe and resolving an outstanding question over its rate. The astronomers used NSF's Very Long Baseline Array, the Karl G. Jansky Very Large Array and the Robert C. Byrd Green Bank Telescope to study the aftermath of the collision of two neutron stars that produced gravitational waves detected in 2017. This event offered a new way to measure the expansion rate of the universe, known by scientists as the Hubble Constant. The expansion rate of the universe can be used to determine its size and age, as well as serve as an essential tool for interpreting observations of objects elsewhere in the universe.
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