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How Fast Is the Universe Expanding? Measuring Cosmic Expansion With Radio Astronomy and Gravitational Waves - SciTechDaily

How Fast Is the Universe Expanding? Measuring Cosmic Expansion With Radio Astronomy and Gravitational Waves - SciTechDaily

How Fast Is the Universe Expanding? Measuring Cosmic Expansion With Radio Astronomy and Gravitational Waves - SciTechDaily
Sep 15, 2020 2 mins, 22 secs

By National Radio Astronomy Observatory.

Artist’s impression of the explosion and burst of gravitational waves emitted when a pair of superdense neutron stars collide?

New observations with radio telescopes show that such events can be used to measure the expansion rate of the Universe.

Astronomers study cosmic expansion by measuring the Hubble constant.

This disagreement, or tension, in the Hubble constant is a growing controversy in astronomy.

Join our host Melissa Hoffman of the National Radio Astronomy Observatory as she explains how astronomers are using radio astronomy and gravitational waves to answer this cosmic mystery.

Astronomers using National Science Foundation (NSF) 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.

Byrd Green Bank Telescope (GBT) 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.

Radio observations of a jet of material ejected in the aftermath of the neutron-star merger were key to allowing astronomers to determine the orientation of the orbital plane of the stars prior to their merger, and thus the “brightness” of the gravitational waves emitted in the direction of Earth.

This can make such events an important new tool for measuring the expansion rate of the Universe.

“The neutron star merger gives us a new way of measuring the Hubble Constant, and hopefully of resolving the problem,” said Kunal Mooley, of the National Radio Astronomy Observatory (NRAO) and Caltech.

The speed divided by the distance yields the Hubble Constant.

When two massive neutron stars collide, they produce an explosion and a burst of gravitational waves.

“This is a completely independent means of measurement that we hope can clarify what the true value of the Hubble Constant is,” Mooley said.

The intensity of the gravitational waves varies with their orientation with respect to the orbital plane of the two neutron stars.

“We think that 15 more such events that can be observed both with gravitational waves and in great detail with radio telescopes, may be able to solve the problem,” said Kenta Hotokezaka, of Princeton University.

Reference: “A Hubble constant measurement from superluminal motion of the jet in GW170817” by K.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

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