Seminar is held on Tuesdays at 13:10 pm in the lecture room of the Institute
on the 10th floor of the department building at Trója, V Holešovičkách 2, Prague 8
Gravitational waves have revolutionized how we observe the Universe. However, current detectors are limited by the overwhelming seismic noise in the low-frequency range. Only space-borne observatories like the future LISA and Taiji missions can reach the rich gravitational wave spectrum in the milliHertz band. Among the sources detectable by space-borne interferometers, extreme-mass-ratio binaries are arguably the most interesting. These systems are composed of a massive black hole and a much smaller compact body. The latter falls into the heavier companion in a slow process called extreme-mass-ratio inspiral (EMRI), emitting gravitational waves with complex features. The properties of an EMRI binary could be recovered from a detected years-long signal with astounding precision, which might lead to exciting discoveries in astrophysics, gravitational, and particle physics. On the other hand, EMRIs are challenging sources to model, and there are still several open problems in data analysis for space detectors. This seminar aims to be an introduction to EMRIs, and is divided into three parts. In the first part, I will overview the theorical tools commonly employed to construct EMRI waveforms, focusing on black hole perturbation theory techniques. I will then introuduce Bayesian statistics applied to gravitational wave data analysis. Finally, I will talk about my current research on parameter estimation for spinning EMRI binaries.
Very large mass-ratio binary black hole systems are expected to radiate low-frequency gravitational waves detectable by planned space-based Laser Interferometer Space Antenna (LISA). We hope to use these systems to probe the spacetime in exquisite detail and make precision measurements of the larger black hole’s properties. Accurate models using general relativistic perturbation theory will allow us to realize the potential of these large mass-ratio systems. Such models must include post-geodesic corrections, which account for forces driving the smaller black hole away from a geodesic trajectory. An important post-geodesic effect is gravitational self-force, which describes the small body's interaction with its own spacetime curvature. This effect includes the backreaction due to gravitational-wave emission that leads to the inspiral of the small body into the black hole. When a spinning body orbits a black hole, its spin couples to the curvature of the background spacetime. This introduces a second post-geodesic correction called the spin-curvature force. In this talk, I will present our calculation of spinning-body inspirals and associated waveforms that include both spin-curvature forces and the leading backreaction of self forces. I will discuss what aspects of the self force have been neglected, and what must be done to include these aspects in the future. Finally, I will discuss how we use a near-identity transformation to eliminate dependence on the orbital phases, allowing for very fast computation of completely generic worldlines of spinning bodies.
We present an approximate time-dependent metric in ingoing Eddington-Finkelstein coordinates for an evaporating nonrotating black hole as a first-order perturbation of the Schwarzschild metric, using the linearized backreaction from a realistic approximation for the stress-energy tensor for the Hawking radiation in the Unruh quantum state.
Jiří Bičák Oldřich Semerák