Search Talks

Coincident detections of electromagnetic and gravitational wave signatures from the merger of supermassive binary black holes are the next observational grand challenge. Such detections will provide a wealth of opportunities to study gravitational physics, accretion physics, and cosmology. Understanding the conditions under which coincidences of electromagnetic and gravitational wave signatures arise during supermassive black hole mergers is therefore of paramount importance, requiring multi-scale/physics computational modeling. I will given an overview of these numerical studies and in particular focus on our effort to model the merger of supermassive black hole binaries in the presence of gaseous environments.

Since its launch in 2007, the website Galaxy Zoo (www.galaxyzoo.org) has become the largest astronomical collaboration in history, involving more than 250,00 volunteers in classifying galaxies. Humans outperform computers at this kind of visual classification, and the results from Galaxy Zoo have been spectacular. As well as reviewing the intimate connections between the delicate process of galaxy formation and the evolution of our Universe, this talk will include a review of the weird and wonderful objects identified by Galaxy Zoo users and a few tales from the ups and downs of citizen science.

We study a novel state of matter: algebraic Bose liquid (ABL). An ABL is a quantum bosonic system on a 2d or 3d lattice that does not break any symmetry in its ground state, but still able to stabilize a gapless spectrum. At high energy these boson systems only have the simplest U(1) global symmetry associated with the conservation of boson number, but at low energy the system is described by self-dual gauge fields. In this talk we will present two new ABL phases emerged from a quantum Boson model on the cubic lattice. At low energy these two ABL phases are described by the linearized z=2 and z=3 Lifshitz gravity respectively. We will show that the self-duality of the field theory is crucial to guarantee the stability of the ABL. References: Cenke Xu, arXiv:cond-mat/0602443, Phys. Rev. B. 74, 224433 Cenke Xu and Petr Horava, arXiv:1003.0009

After prodigious work over several decades, binary black hole mergers can now be simulated in fully nonlinear numerical relativity. However, these simulations are still restricted to mass ratios q = m2/m1 > 1/10, initial spins a/M < 0.9, and initial separations r/M < 10. Fortunately, analytical techniques like black-hole perturbation theory and the post-Newtonian approximation allow us to study much of this region in parameter space that remains inaccessible to numerical relativity. I will use black-hole perturbation theory to establish a fundamental upper limit to the final spin that can be attained through binary mergers, and show how this limit can be used to improve predictions of final spins for finite mass ratios as well. I will also show that post-Newtonian inspirals between 1000 M < r < 10 M can align or anti-align black hole spins with each other, dramatically changing the distributions of final spins and recoil velocities that would be expected in astrophysical black hole mergers.