The Era of Binary Supermassive Black Holes: Coordination of Nanohertz-Frequency Gravitational-Wave Follow-up

TL;DR

This paper summarizes a 2025 conference focused on coordinating electromagnetic and gravitational-wave follow-up strategies for detecting binary supermassive black holes via pulsar timing arrays, emphasizing multi-messenger approaches.

Contribution

It provides a comprehensive overview of current knowledge, identifies gaps, and proposes a roadmap for electromagnetic follow-up of gravitational-wave detections of supermassive black hole binaries.

Findings

Facilitated interdisciplinary knowledge exchange.

Outlined key considerations for multi-messenger follow-up.

Proposed a roadmap for future electromagnetic counterpart searches.

Abstract

Here we summarize discussions and conclusions from the conference ``The Era of Binary Supermassive Black Holes: Coordination of Nanohertz-Frequency Gravitational-Wave Follow-up,'' held at the Aspen Center for Physics from February 2-7, 2025. The meeting facilitated a crucial knowledge exchange between electromagnetic and gravitational-wave theorists, observers, and cyber-infrastructure experts. The central goal was to guide the development of multi-messenger follow-up strategies for binary supermassive black hole detections by pulsar timing arrays. To build a common basis of understanding for the broader scientific community, this summary outlines the main considerations and recommendations from the meeting, summarizes the knowledge gaps identified, and ends with a potential roadmap to catalyze discussion about the search for electromagnetic counterparts to massive black hole binaries detected by pulsar timing arrays.