Session T05: Astrophysics with Ground-Based Gravitational-Wave Observations

Live

The gravitational-wave observations of LIGO and Virgo have uncovered a population of binary black holes. The component masses of some of these detected binaries potentially encroach on the theorized pulsational pair-instability mass gap, where black holes are not expected to be formed directly from stars. We consider an alternate formation channel, where black holes are formed dynamically from previous binary black hole mergers, potentially explaining observation of more massive black holes. Creating a binary black hole population that allows for this hierarchical formation channel, we use the catalog of LIGO and Virgo observations to infer the black hole population parameters, as well as the branching ratios between generations. We use the result to calculate odds ratios in favor of individual binary black hole mergers being of hierarchical origin. By providing a better understanding of the population of black holes, our results shed light on the physics of black hole formation.   

Live

Gravitational waves carry energy, angular momentum, and linear momentum. For generic binary black holes, the loss of linear momentum imparts a recoil velocity or a “kick” to the remnant black hole produced by the merger. We exploit recent advances in gravitational waveform and remnant black hole modeling to measure both the kick magnitude and direction from gravitational wave signals. We find that very little information can be gained about the kick velocity for existing gravitational wave events, but that interesting measurements will soon become possible as the detectors improve. We show that, once LIGO and Virgo reach their design sensitivities, we will reliably measure the kick velocity for generically precessing binaries, including the so-called superkicks reaching up to 5000 km/s. Kick measurements such as these are fundamentally interesting as probes of the ability of gravitational fields to carry linear momentum. They can also be used to place an independent constraint on the rate of second-generation binary mergers. Finally, we show that the kick must be factored into tests of general relativity with third-generation gravitational wave detectors to avoid Doppler-induced biases in the remnant mass as measured from the ringdown alone.   

Live

The discoveries of compact binary mergers by LIGO and Virgo have allowed to start characterizing the astrophysical population of binary black holes; e.g. the distribution of masses and spins, which carry information about their origin. Still, these efforts are currently limited by the relatively small number of detections. Recently, we developed an independent pipeline to analyze public LIGO data and identified eight new binary black hole mergers, roughly doubling the sample of these systems. In this talk I will describe the constraints we obtain on the properties of binary black holes when we include these new events and marginal triggers.   

Live

LIGO and Virgo detections over the past four years have ushered in the new era of multi-messenger physics and astronomy. Gravitational-wave observations can be used to test general relativity in dynamical spacetimes, to gain new insights into the nature of matter under extreme physical conditions of gravity, density, and pressure, to discover the nature of dark matter, dark energy and other exotic objects, to explore the nature of most violent processes in the Universe, to study the formation and evolution of stellar mass black holes throughout the Universe and to probe the physics of the early history and evolution of the Universe. The science case for building Cosmic Explorer and Einstein Telescope that can probe deep into the cosmos and observe a variety of different processes is immensely rich and massively rewarding.   

Live

Gravitational wave astronomy has opened a new window to study astrophysical objects and phenomena, the early universe, and the fundamental physics of gravity. Compact binaries are among the most luminous gravitational-wave sources and present a great probe for a wide range of physical phenomena. Hence it is important to improve the accuracy with which we can determine the properties of these systems, increase the efficiency of multi-messenger follow-up observations, and expand the observable range to encompass most populations of binaries in our universe. Focusing on the needs of such compact binary observations, we examine in this trade study the capability of different configurations of the next generation US ground-based gravitational wave detector Cosmic Explorer embedded in the global network of KAGRA and LIGO-India detectors as well as the Einstein Telescope. Using Fisher analysis methods, we compare various network combinations with and without Cosmic Explorer in different configurations to determine the minimum setup necessary that would allow significant scientific progress in our understanding of the astrophysics of binary black holes and neutron stars.   

On Demand

The recent observations of stellar mass black hole binaries by Advanced LIGO and Advanced Virgo have revived interest in the possibility of sub-solar mass ultracompact objects. Due to the lack of knowledge surrounding the composition of sub-solar mass ultracompact objects, they have long been of interest as a potential dark matter candidate. Since astrophysical processes are not expected to produce ultracompact objects below one solar mass, the detection of such an object could therefore be an indication of new physics. We present proposed future searches and the parameters of interest for sub-solar mass ultracompact objects with LIGO, Virgo, and KAGRA.   

On Demand

We use a combination of principal component analysis and Markov Chain Monte Carlo techniques to estimate how accurately third-generation observatories, like the planned Cosmic Explorer detector, will measure the properties of a core collapse supernova from its gravitational-wave radiation. Using a mapping for rotation rate of the core of the star between the principal components obtained from a catalog of core collapse waveforms and the morphology of the gravitational-wave signal, we obtain posterior probability distributions on the coefficients of the principal components and translate these to posteriors on the rotation rate using the above map. We also obtain posteriors on the frequency of the postbounce oscillations of the protoneutron star, from which we can infer the nuclear equations of state consistent with the signal waveform.   

Observing neutron stars with Cosmic Explorer and Einstein Telescope

As ground-based gravitational-wave astronomy improves in sensitivity over the coming decades, a universe of neutron-star mergers will come into view. I will outline the expected sensitivity to the population of neutron-star binaries for observatories like Cosmic Explorer and Einstein Telescope, which aim to record such mergers from redshifts of order 2 or beyond. For nearby mergers, precision measurements of orbital dynamics will be possible, and I will describe the capabilities of future observatories to determine neutron-star tidal interactions and the properties of dense matter.   

Not Participating

The LIGO HET Response (LIGHETR) project is a group of several institutions performing spectroscopic followup of gravitational wave sources discovered by the LIGO/Virgo collaboration (LVC). LIGHETR uses two integrated field unit spectrographs (IFUs) with deep coverage in the blue, VIRUS and LRS2, both mounted on the 11 m Hobby Ebberly Telescope (HET). Our strategy is to target the most probable galaxies within the LVC sky-map, with the aim to acquire the earliest, rapidly varying, blue \textit{spectra} of the electromagnetic counterparts. Alternatively, we also perform follow-up on transient candidates identified by other observatories. The unique challenges of the observations (fixed zenith angle, IFUs) necessitate custom pipelines for rapid observation planning and data reductions using novel techniques which will be presented here.