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# 4. Using GW170817 to Measure the Expansion Rate of the Universe

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#### About this Lecture

Lecture

In this mini-lecture, we consider a specific gravitational wave event, GW 170817, that helped us measure the expansion rate of the Universe. As we move through this mini-lecture, we consider: (i) the GW 170817 detection from two colliding neutron stars, which was in both gravitational wave signal and electromagnetic radiation; (ii) the characteristic chirp sound from this collision, which describes the frequency of the gravitational waves as the stars get closer together; (iii) the gamma ray burst and kilonova produced by this neutron star merger that helped us determine the host galaxy; (iv) an aside on how the kilonova spectrum indicated the neutron star collision produced precious, heavy metals; (v) the measurement of the Hubble constant, i.e. the expansion rate of the Universe, using the data collected from GW 170817; (vi) the need for more data and more mergers to get a more accurate measurement of the Universe’s expansion rate; and (vii) how to find the redshift of the host galaxy of a gravitational wave’s source when no light is emitted.

Course

In this course, Professor Martin Hendry (University of Glasgow) discusses how we can use gravitational wave detections to help us refine our measurement of the expansion rate of the Universe. In the first mini-lecture, we introduce gravitational waves, first as a prediction made by Einstein in his theory of gravity and then as an observation made nearly 100 years later with the LIGO interferometer detectors. In the second mini-lecture, we discuss Edwin Hubble’s work that led to the discovery of the expansion of the Universe and how his work has been extended in more recent times. In the third mini-lecture, we discuss how gravitational waves can be used to help us find the expansion rate of the Universe, and in the fourth mini-lecture, we look at a specific event, GW 170817, that allowed us to make the first measurement of the Universe’s expansion rate using gravitational waves. In the fifth mini-lecture, we consider some notable gravitational wave detections and what the future holds.

Lecturer

Martin Hendry is a Professor of Gravitational Astrophysics and Cosmology at the University of Glasgow. His primary research interests lie in gravitational wave astronomy, statistical methods for the analysis of astrophysical and cosmological data sets, and applications of gravitational lensing. He is a member of the LIGO Scientific Collaboration (LSC), which has been awarded the 2016 Special Breakthrough Prize for Fundamental Physics, the Physics World Breakthrough of the Year for 2016 and 2017, and the President's Medal of the Royal Society of Edinburgh. He serves as the chair of LSC Education and Public Outreach group and is the co-chair of the Advocacy and Outreach Group of the recently established International LISA Consortium. Professor Hendry is also an elected follow of the Royal Society of Edinburgh and a fellow of the Institute of Physics (IOP), serving as chair of the IOP in Scotland from 2015-2017. In 2010, he was invited by Learning and Teaching Scotland to join the Maths Excellence Group and Physics Qualifications Design Team for the Curriculum for Excellence, where he helped to redesign the high school physics curriculum in Scotland. He has won various awards in public outreach, including the Royal Society of Edinburgh’s Senior Prize for public engagement.

#### Cite this Lecture

**APA style**

Hendry, M.
(2022, January 14).
*Using Gravitational Waves to Measure the Expansion of the Universe - Using GW170817 to Measure the Expansion Rate of the Universe* [Video]. MASSOLIT. https://massolit.io/courses/using-gravitational-waves-to-measure-the-expansion-of-the-universe/using-gw170817-to-measure-the-expansion-rate-of-the-universe

**MLA style**

Hendry, Martin.
"Using Gravitational Waves to Measure the Expansion of the Universe – Using GW170817 to Measure the Expansion Rate of the Universe." *MASSOLIT*, uploaded by MASSOLIT,
14 Jan 2022,
https://massolit.io/courses/using-gravitational-waves-to-measure-the-expansion-of-the-universe/using-gw170817-to-measure-the-expansion-rate-of-the-universe