Session B3: Neutron Stars: What's the Matter?

Numerical Simulations of Binary Systems with Matter Companions

With the advent of gravitational wave interferometers such as LIGO, VIRGO, and LISA, a revolution in astronomy and relativistic astrophysics is about to begin. Compact objects---black holes (BHs), neutron stars (NSs), and white dwarfs (WDs)---in binary systems are among the most promising sources of gravitational radiation detectable by these interferometers. In addition, merging compact object binaries with matter companions may also emit a detectable electromagnetic counterpart, leading to an exciting possibility: a simultaneous detection of both gravitational and electromagnetic radiation. Such a detection could lead to breakthroughs in our understanding of matter under extreme conditions, as there are currently many competing ideas about how this matter should behave. Determining the correct one will require careful modeling of the gravitational and electromagnetic waves these systems emit through the late- inspiral, merger, and post-merger stages. During these stages, the effects of high-velocity, strong-field gravitation become paramount, and accurate modeling requires large-scale, fully general relativistic simulations. I will review some of the latest results from fully general relativistic simulations of compact object binaries with matter companions, including NSNSs, BHNSs, and WDNSs. These simulations examine the effects of mass ratio, BH spin, equations of state, and magnetic fields on the gravitational waveforms and possible electromagnetic counterparts. Future work will focus on producing longer gravitational waveforms, incorporating more physics, and inventing new algorithms to efficiently handle the disparate length and timescales.   

Measuring the neutron-star equation of state using gravitational waves from binary observations

Learning about the size and structure of neutron stars is a challenging problem in astrophysics. These properties are related to the uncertain equation of state for matter above nuclear density. For most of the inspiral of a binary neutron star system, matter effects are unmeasurable, and the stars are well-modeled by point particles. However, as the neutron stars approach each other, an equation-of-state dependent tidal deformation modifies their orbits, changing the late inspiral waveform. This may be measurable in advanced ground-based detectors. I will discuss the size of these effects for realistic equations of state, using waveform estimates based on post- Newtonian and based on high-accuracy numerical simulations of binary neutron stars.   

Searching for gravitational waves from compact binary coalescence

The coalescence of compact binary objects is a brilliant source of gravitational radiation. Close binary systems comprised of neutron stars and or stellar mass black holes will emit gravitational waves at frequencies detectable by ground based, gravitational wave observatories. Gravitational wave searches targeting coalescing compact objects have been in- the-works for over a decade and should result in the first direct observation of coalescence within the coming decade. In this talk I will provide some of the history of these searches as well as summarize the most recent results and prospects for the future.