Uncovering the Mystery of the Universe's Expansion Rate with Gravitational-Wave Observations

This award supports research in gravitational-wave cosmology. With the first detection of gravitational-wave signals, ripples in the space-time, by NSF's LIGO, a new window to the Universe has been opened. The observations of gravitational-wave signals emitting from merging black holes and neutron stars brought about enormous advances in astrophysics, nuclear physics, fundamental physics, and cosmology. In particular, combining the gravitational-wave and electromagnetic-wave observations of binary mergers enables the measurement of the local Universe expansion rate. Under this award, the UT-Austin team will develop data analysis tools to measure the Universe expansion rate with upcoming gravitational-wave and electromagnetic-wave observations. The research activities will provide theoretical and data analysis training for graduate students. In addition, the award supports the development of websites and workshops to encourage public engagement in gravitational-wave science. The local Universe expansion rate, the Hubble constant, can be measured by a wide range of methods. However, a perplexing tension between different Hubble constant measurements has brought enormous efforts and resources into resolving the tension over the last decade. No consensus has been reached so far. This is where gravitational-wave observations can play a critical role. With the method known as the "standard siren", gravitational-wave observations have great potential to shed light on one of the biggest mysteries in modern cosmology. Focusing on the systematic uncertainties of standard sirens, the UT-Austin team will quantify the systematics from electromagnetic counterpart emissions and develop techniques to mitigate them. The team will then prepare a standard siren measurement pipeline that adopts the latest developments in the field and publicly available data in order to measure the Hubble constant to great precision and accuracy. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.