Gravitational Wave Sources from Dense Star Clusters

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Most stars form in dense clusters. The largest star clusters contain many millions of stars. The masses of these stars, when born, cover a broad range. The most massive stars end their lives in as little as a few million years and leave behind remnant black holes or neutron stars. Much larger numbers of massive white dwarf remnants are produced from intermediate-mass stars in a few billion years. The star clusters themselves often continue to live for many billions of years. Therefore, many of the star clusters observed today can contain large numbers of black holes and neutron stars formed a long time ago, as well as large populations of white dwarfs. The investigators will use computer simulations to study the dynamical interactions of all compact remnants (black holes, neutron stars, and white dwarfs) in dense star clusters. These models will help astronomers interpret observational data. This work also has applications beyond astronomy. In particular, the computing methodology developed for this work will be of interest to scientists outside of physics and astronomy, since the techniques used to model dense clusters of interacting stars have broad relevance in science and engineering. This work will also help maintain the investigators' student-oriented research program in computational astrophysics. The graduate students involved will mentor and work closely with undergraduate students. The investigators will strive to recruit students from traditionally underrepresented groups. Education and public outreach activities will take advantage of the investigators' close ties to the Adler Planetarium in Chicago and the Dearborn Observatory on the Northwestern University campus. State-of-the-art N-body simulations will be performed to study the formation and evolution of compact objects in a variety of star cluster environments. The main focus will be on the production of compact binaries, which can be strong sources of gravitational waves and high energy radiation, as well as transient sources triggered by collisions and close encounters of compact objects. The work will address key questions concerning the formation and dynamical evolution of compact objects in dense star clusters, including their strong interactions with other stars. The electromagnetic transients produced through interactions of compact remnants with other stars potentially include a variety of X-ray and gamma-ray burst sources, as well as many optical transients of great current interest in the new era of large time-domain astronomy surveys. Additionally, all compact binaries formed through dynamical interactions are strong sources of gravitational waves, and some will have strong electromagnetic counterparts, making them key targets for multi-messenger astronomy. This award thus advances the goals of the NSF's "Windows on the Universe: The Era of Multi-Messenger Astrophysics" Big Idea.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.