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The Era of Binary Supermassive Black Holes

This Aspen conference will focus on clarifying how to succeed with identification of host galaxies of binary supermassive black holes (MBHs) through coordination between pulsar timing arrays (PTAs) and electromagnetic instruments.

PTAs are expected to begin resolving individual binary MBHs from the gravitational-wave background in the next few years. The first few detections from PTAs will represent the first conclusive identifications of binary supermassive black holes, however will be poorly localized on the sky, potentially spanning regions of up to several thousand square degrees (containing 100’s to 1000’s of candidate galaxies). Therefore, extensive follow-up observations with a broad range of upcoming astrophysical instruments, coupled with historical archives to track long-term signal evolution, will be required to conclusively identify the host galaxies of these systems.

Building toward the first CW detection, significant questions remain that can only be brought through a timely discussion between PTA scientists, electromagnetic observers, and theorists. These critical questions include:

  • How can upcoming electromagnetic surveys optimize the balance of sensitivity/field of view for the MMA identification of PTA detections?

  • How can PTA and electromagnetic observing communities leverage the large ecosystem of multimessenger coordination infrastructure that have been developed for high-frequency gravitational-wave observations?

  • What theorized electromagnetic signatures of binary MBHs require further inspection, and do current/future facilities enable observations of them?

  • Are there critical observing capabilities for this science case that are not going to be realized by planned facilities?

As we enter this significant era of first discovery, coordination is crucial: rich science will come from the identification of host galaxies of continuous-wave detections. This pursuit will necessarily involve a broad-strokes multi-wavelength effort, coordinated between PTAs, astronomical archives, new wide-field surveys, and new targeted observations. In this era of imminent continuous-wave detections by PTAs, it will be important to provide a roadmap towards observational coordination between these efforts. This workshop will draw a broad range of electromagnetic and gravitational-wave observers, large-survey scientists, and astronomy cyber-infrastructure scientists, to plan and coordinate such follow-up. We anticipate that this Aspen meeting will facilitate new collaborations and lead to significantly accelerated progress in this field.

This conference will include workshop-style elements, bringing together critical players in PTA continuous-wave searches, MBH binary evolution theory, MBH binary observation, multi-messenger cyberinfrastructure, and astronomical observing and archiving facilities to address the above questions and build new collaborative links across the multi-messenger spectrum.

Scientific Organizing Committee:

Sarah Burke-Spolaor (Chair,
Tamara Bogdanovic
Mike Eracleous
Matthew Graham
Kayhan Gultekin (
Jeffrey Hazboun (
Chiara Mingarelli (
Gautham Narayan

About the Aspen Center for Physics

The essence of the work at the Aspen Center for Physics lies in thought and communication. Set in a friendly, small town of inspiring landscapes, the Center is conducive to deep thinking with few distractions, rules or demands. In our "circle of serenity," physicists work at their own speeds and in their own ways: alone or together, at the desk, at the blackboard or in a chair on the lawn. Spontaneous discussions give rise to new collaborations.

The Center encourages individual and collaborative research and offers summer workshops and winter conferences in biophysics, astrophysics and cosmology, particle physics, and condensed matter physics. Cross-scientific workshops with other disciplines are scheduled when physics is central to the topic. Each year, over 1,000 scientists from around the world visit the Center to explore new research on the unanswered questions about our world and universe.

Physicists share their cutting-edge research with Aspen locals and visitors during the free Heinz R. Pagels and Maggie and Nick DeWolf lecture series. Informal physics dialogues and cafés give the audience additional opportunities to ask questions and engage in conversations. In the summer, the Center co-hosts a weekly picnic for children and their families with the Aspen Science Center. After the picnic, our physicists introduce big ideas to children of all ages.

Our goal is simple: fine minds in an atmosphere of creative freedom.