Probing supermassive black hole evolution with pulsar timing arrays
Lead Research Organisation:
UNIVERSITY OF BIRMINGHAM
Abstract
Pulsar timing arrays (PTAs) have recently found evidence for a stochastic gravitational-wave background (GWB), ushering in the era of nanohertz GW astronomy. The primary contributor to the GWB at nanohertz frequencies is believed to be a collection of supermassive black hole binaries (SMBHBs). However, the potential for other exotic sources like cosmic strings, inflation, or early universe phase transitions remains. Distinguishing among these sources hinges on identifying resolvable SMBHBs. These are anticipated to be detectable as quasi-monochromatic continuous waves within the next few years. Detecting a resolvable SMBHB will not only confirm the source of the GWB but will also yield vast scientific developments. It could illuminate the evolution of such binaries (particularly relevant in light of recent JWST discoveries of SMBHBs at high redshift), facilitate multi-messenger astronomy, and enable novel tests of general relativity.
Because PTA research has been focusing on the GWB, methods for robustly identifying and characterising resolvable SMBHBs are lacking. This project will address this issue by developing novel techniques and applying them to candidate signals in the latest datasets of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) and the International Pulsar Timing Array (IPTA). The project is organized in two work packages:
Robust SMBHB candidate vetting: we will develop novel Bayesian statistical methods to ascertain the binary origin of candidate signals and distinguish them from other sources that may mimic an SMHBH signal. This work is extremely timely, as the most recent analyses of the European Pulsar Timing Array (EPTA) and the NANOGrav already found a tantalising hint of a resolvable SMBHB signal, which sparked community-wide interest in a reliable candidate vetting process. We will apply our novel validation techniques on this and any other candidates identified in the latest datasets of NANOGrav and IPTA.
2. Sophisticated SMBHB characterisation: we will develop methods to go beyond the current state-of-the-art of modelling SMBHBs as having non-spinning black holes in vacuum on circular orbits. Eccentricity, spin effects and drag from a gaseous circumbinary disk can affect the frequency evolution of the binary. The motivation for including these effects in the model is twofold: i) mapping the frequency evolution of an SMBHB can provide invaluable insight on the as yet poorly understood evolutionary phase of SMBHBs when they reach sub-parsec separations; ii) even if these effects are not confidently detectable in a given system, ignoring them can lead to significant bias (so-called stealth bias), which can invalidate all downstream analysis and can lead to telescope time wasted during electromagnetic (EM) follow-up. The latter is particularly important in these early years of PTA science, because efforts are already being made to plan early EM follow-up of candidates. This is crucial given the long observation periods required for EM identification of a binary, however, accurate characterisation, especially estimating the source's mass and distance, is vital to optimise the use of EM resources. We will use this new approach to analyse candidates in the latest IPTA dataset and provide robust estimates of their astrophysical parameters.
Because PTA research has been focusing on the GWB, methods for robustly identifying and characterising resolvable SMBHBs are lacking. This project will address this issue by developing novel techniques and applying them to candidate signals in the latest datasets of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) and the International Pulsar Timing Array (IPTA). The project is organized in two work packages:
Robust SMBHB candidate vetting: we will develop novel Bayesian statistical methods to ascertain the binary origin of candidate signals and distinguish them from other sources that may mimic an SMHBH signal. This work is extremely timely, as the most recent analyses of the European Pulsar Timing Array (EPTA) and the NANOGrav already found a tantalising hint of a resolvable SMBHB signal, which sparked community-wide interest in a reliable candidate vetting process. We will apply our novel validation techniques on this and any other candidates identified in the latest datasets of NANOGrav and IPTA.
2. Sophisticated SMBHB characterisation: we will develop methods to go beyond the current state-of-the-art of modelling SMBHBs as having non-spinning black holes in vacuum on circular orbits. Eccentricity, spin effects and drag from a gaseous circumbinary disk can affect the frequency evolution of the binary. The motivation for including these effects in the model is twofold: i) mapping the frequency evolution of an SMBHB can provide invaluable insight on the as yet poorly understood evolutionary phase of SMBHBs when they reach sub-parsec separations; ii) even if these effects are not confidently detectable in a given system, ignoring them can lead to significant bias (so-called stealth bias), which can invalidate all downstream analysis and can lead to telescope time wasted during electromagnetic (EM) follow-up. The latter is particularly important in these early years of PTA science, because efforts are already being made to plan early EM follow-up of candidates. This is crucial given the long observation periods required for EM identification of a binary, however, accurate characterisation, especially estimating the source's mass and distance, is vital to optimise the use of EM resources. We will use this new approach to analyse candidates in the latest IPTA dataset and provide robust estimates of their astrophysical parameters.
Organisations
People |
ORCID iD |
| Bence Becsy (Principal Investigator) |