Northwestern University

Wed 12:00 PM

Brown Bag Lunch Series

recurring see all events in this series

When: Wednesday, May 16, 2018
12:00 PM - 1:00 PM  

Where: Technological Institute, F160, 2145 Sheridan Road, Evanston, IL 60208 map it

Audience: Faculty/Staff - Student - Post Docs/Docs - Graduate Students

Contact: Bud Robinson   847.491.3644

Group: Physics and Astronomy Brown Bag Lunch Seminars

Category: Academic


How Black Holes Shape Globular Clusters

Kyle Kremer

Numerical simulations have shown that black holes (BHs) can strongly influence the evolution and present-day observational properties of globular clusters (GCs). Using a Monte Carlo code, we construct GC models that match the Milky Way (MW) cluster NGC 3201, the first cluster in which a stellar-mass BH was identified through radial-velocity measurements. We predict that NGC 3201 contains > 200 stellar-mass BHs. Furthermore, we explore the dynamical formation of main sequence-BH binaries and demonstrate that systems similar to the observed BH binary in NGC 3201 are produced naturally. Additionally, our models predict the existence of bright blue-straggler-BH binaries unique to core-collapsed clusters, which otherwise retain few BHs.

The Role of Binary-Binary Encounters in Inducing Eccentric Gravitational-Wave Inspirals

Michael Zevin

The multiple discoveries of coalescing binary black hole systems by the advanced network of gravitational-wave interferometers have enticed exploration into mechanisms responsible for their formation and subsequent merger. We perform scattering experiments of binary-single and binary-binary black hole interactions from realistic cluster models with post-Newtonian dynamics included. By including post-Newtonian effects in the equations of motion, the dissipation of orbital energy from the emission of gravitational radiation can lead to inspirals and mergers during resonant interactions, oftentimes with measurable eccentricities when entering the LIGO sensitive frequency range. Though less frequent, we find that binary-binary interactions are much more efficient at inducing inspirals than their binary-single counterparts, accounting for ~20--30% of in-cluster mergers, depending on the properties of the cluster environment. Binary-binary interactions also readily form stable, hierarchical triple systems that undergo Lidov-Kozai oscillations which over periods of time will impart orbital eccentricity into the inner binary. The gravitational waveforms of eccentric inspirals are distinct from those generated by merging binaries which have circularized, and observations of such systems would highly constrain their formation scenario.

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