## International Summer Research Program in Gravitational-Wave Physics:

Research Experiences for Undergraduates around the world

**Monash University**

- Inferring the properties of primordial black holes with gravitational waves:

Around every 200 seconds, a pair of stellar mass black holes merge somewhere in the Universe. A small fraction of these mergers are detected as individually resolvable gravitational-wave events by detectors such as advanced LIGO and Virgo. The rest contribute to a stochastic background. Observing this gravitational-wave background will allow us to study black holes at redshifts much higher than at which LIGO/Virgo could resolve individual sources. Some of the black holes observed by LIGO/Virgo may be “primordial” black holes, formed in regions of high density in the early universe rather than through stellar collapse. There has been renewed interest in primordial black holes as a candidate for dark matter since the first observation of gravitational waves from binary black hole mergers. This project will explore our ability to extract information about primordial black holes from the gravitational wave background using current and planned detectors.

**Mentor:**Rory Smith

**Related Project 2018:**"Inferring the binary black hole redshift distribution"

- Ensemble gravitational wave detections: more than the sum of the parts:

Gravitational-wave astronomy is now a reality. In February 2016, LIGO announced the first direct detection of gravitational waves from the collision of two black holes, each with mass approximately 30 times that of the Sun. From the first observing run of Advanced LIGO, two bona fide detections were made of binary black hole mergers, and one further candidate detection. These detections allow us to predict the event rate of future detections given the planned improvement in instrument sensitivity. The future is very bright with tens to hundreds of detections expected in the next two or three years. In this project, we will explore physics that can be learned from an ensemble of gravitational wave detections that cannot be learned from any given detection. For example, we recently published a paper (see "Detecting Gravitational-Wave Memory with LIGO: Implications of GW150914" in PRL or the arXiv) showing that gravitational-wave memory — a permanent deformation of spacetime following the emission of gravitational waves — can be detected confidently once approximately 30 loud binary black hole mergers have been detected with Advanced LIGO. Potential projects involve looking for deviations from General Relativity in ultra-strong gravitational fields or trying to understand how these stellar-mass black holes formed in the first place.

**Mentors:**Paul Lasky and Eric Thrane

**Related Project 2018:**"Fitting Binary Black Hole Populations with Phenomenological Models"

- Black Hole Paleontology

Gravitational-wave detectors have, for the first time, observed signatures of binary black hole mergers. These black holes are remnants of massive stars which burned bright and died young, and observations of their fossils will tell us much about how they evolved. To do this, however, we need to develop better astrophysical models of binary evolution, extract the information that gravitational waves carry about the mas ses and spins of the binary components, and compare multiple observations with libraries of models. In this project, you will learn about the astrophysics of binary stars and combine astrophysical models, modern data analysis techniques, and astro-statistics to explore black-hole paleontology.

**Mentor:**Ilya Mandel

**Related Project 2012:**"Improving Parameter Estimation on Gravitational-Wave Signals"

**Related Project 2013:**"Parameter Estimation Accuracy in Hybrid Gravitational Waveform Modeling"

**Past Projects with Monash University faculty**

- What can we learn about Black Holes with Gravitational Waves?

One of the main goals of gravitational-wave searches lies in the possibility of inferring the parameters of the sources from their gravitational-wave signature. For coalescing compact binaries, the parameter space can be quite large, e.g. 15 parameters for black-hole binaries with arbitrary spins. The presence of strong correlations and degeneracies in this large parameter space brings up a variety of challenges in searching for the true source parameters. We typically use stochastic techniques, such as Markov Chain Monte Carlo, to sample this parameter space. These techniques rely on accurate models of gravitational waveforms. We will explore the accuracy requirements for waveforms models, account for uncertainty in the waveforms, and develop techniques for computationally efficient parameter estimation on very long-duration waveforms.

**Mentor:**Ilya Mandel

**Related Project 2012:**"Improving Parameter Estimation on Gravitational-Wave Signals"

**Related Project 2013:**"Parameter Estimation Accuracy in Hybrid Gravitational Waveform Modeling"

- Improving Parameter Estimation on Gravitational-Wave Signals:

One of the main goals of gravitational-wave searches lies in the possibility of inferring the parameters of the sources from their gravi tational-wave signature. For coalescing compact binaries, the parameter space can be quite large, e.g. 15 parameters for black-hole binaries wi th arbitrary spins. The presence of strong correlations and degeneracies in this large parameter space brings up a variety of challenges in sear ching for the true source parameters. We typically use stochastic techniques, such as Markov Chain Monte Carlo, to sample this parameter space. These techniques can be made more efficient by gaining a better understanding of the expected correlations. The goal of this project will be to search for such correlations and use the gained knowledge to improve jump proposal distributions.

**Mentor:**Ilya Mandel

**Related Project 2012:**"Improving Parameter Estimation on Gravitational-Wave Signals"

**Related Project 2013:**"Parameter Estimation Accuracy in Hybrid Gravitational Waveform Modeling"

**Past IREU Projects**

**Other Prior Projects**