Science with the space-based interferometer eLISA. I: Supermassive black hole binaries

Abstract: We compare the science capabilities of different eLISA mission designs, including four-link (two-arm) and six-link (three-arm) configurations with different arm lengths, low-frequency noise sensitivities and mission durations. For each of these configurations we consider a few representative massive black hole formation scenarios. These scenarios are chosen to explore two physical mechanisms that greatly affect eLISA rates, namely (i) black hole seeding, and (ii) the delays between the merger of two galaxies and the merger of the black holes hosted by those galaxies. We assess the eLISA parameter estimation accuracy using a Fisher matrix analysis with spin-precessing, inspiral-only waveforms. We quantify the information present in the merger and ringdown by rescaling the inspiral-only Fisher matrix estimates using the signal-to-noise ratio from non-precessing inspiral-merger-ringdown phenomenological waveforms, and from a reduced set of precessing numerical relativity/post-Newtonian hybrid waveforms. We find that all of the eLISA configurations considered in our study should detect some massive black hole binaries. However, configurations with six links and better low-frequency noise will provide much more information on the origin of black holes at high redshifts and on their accretion history, and they may allow the identification of electromagnetic counterparts to massive black hole mergers.

• The paper evaluates various eLISA designs, comparing four-link and six-link configurations with different arm lengths and noise thresholds.
• It employs Fisher matrix analysis and waveform modeling to accurately estimate parameters of high-redshift supermassive black hole mergers.
• Findings suggest that enhanced sensitivity and design optimization improve multimessenger astronomy and our understanding of MBH evolution.

Overview of eLISA's Science Capabilities for Supermassive Black Hole Binaries

The paper "Science with the space-based interferometer eLISA: Supermassive Black Hole Binaries" conducts a comprehensive analysis of the scientific potential of different designs of the eLISA mission for the study of supermassive black hole binaries (SMBHBs). eLISA, the evolved Laser Interferometer Space Antenna, represents a key mission in gravitational wave astrophysics, aimed at probing the low-frequency gravitational wave spectrum in the universe. The authors focus on how different configurations of eLISA could influence the mission's ability to achieve significant astrophysical insights into the formation and evolution of massive black holes (MBHs) and their host galaxies.

Mission Design Considerations

The study examines six core configurations of eLISA characterized by varying arm lengths, noise sensitivities, and laser link numbers, which correspond to practical engineering and financial constraints. The configurations analyzed include four-link (two-arm) and six-link (three-arm) designs, with arm lengths ranging from 1, 2, to 5 million kilometers. These configurations differ in their expected sensitivity to low-frequency gravitational waves, potentially impacting the mission's capabilities.

Astrophysical Scenarios

The authors consider multiple SMBHB formation scenarios to evaluate eLISA's performance. These scenarios explore different physical mechanisms affecting SMBHB merger rates: the initial seeding of black holes and the delay times between galaxy mergers and the consequent black hole mergers. By employing various theoretical models, including those involving light and heavy seed formation theories alongside associated merger delays, the study assesses how eLISA can discern between different evolutionary pathways of black holes in the universe.

Parameter Estimation

For estimating the accuracy of the eLISA configurations, the study employs Fisher matrix analysis using spin-precessing, inspiral-only waveforms, and assesses the additional information brought by merger and ringdown phases using phenomenological waveform models. The results indicate that all eLISA designs will detect SMBHBs, but configurations featuring longer arms and lower noise thresholds significantly improve the chances of detecting high-redshift events, which are crucial for understanding the early Universe.

Implications and Future Developments

The analysis suggests several implications for the eLISA mission. Configurations with six links and superior low-frequency noise sensitivity offer more comprehensive information on the history of MBHs and may enable the identification of electromagnetic counterparts, enhancing multimessenger astronomy. These findings inform the optimization of eLISA to maximize scientific returns, particularly concerning the mission's ability to study the SMBHB population across cosmic time.

The paper concludes by speculating on future developments in gravitational wave astronomy that could benefit from eLISA's observations, such as improving the precision of our understanding of MBH growth mechanisms and testing general relativity in strong gravitational fields. These advancements promise to significantly contribute to astrophysics and our knowledge of the universe's structure and evolution.