Periodic Reporting for period 4 - B Massive (Binary massive black hole astrophysics)
Okres sprawozdawczy: 2024-03-01 do 2025-02-28
The Action B Massive is framed in the context of theoretical and observational astrophysics, the branch of science that has the goal of understanding the evolution of the Universe and of the astrophysical objects (from galaxies to planets) within it. Among those, massive black hole binaries are perhaps the most extreme, fascinating yet elusive ones. In fact, as the mutual gravitational pull causes galaxies to merge with each other frequently along cosmic history, the massive black holes hosted at their center are expected to sink into the nucleus of the merger remnant and form a binary. Still, the evidence of the existence of these binaries is sparse and their role in galaxy evolution is poorly understood. Establishing observationally their existence will be a milestone for contemporary astronomy, providing a fundamental missing piece in the puzzle of galaxy formation, piercing through the (hydro)dynamical physical processes shaping dense galactic nuclei from parsec scales down to the event horizon, and probing gravity in extreme conditions.
We can both see and listen to massive black hole binaries. Remarkably, besides arguably being among the brightest objects shining in the Cosmos, they are also the loudest gravitational wave sources in the Universe. As such, we shall take advantage of both the type of messengers – photons and gravitons – they are sending to us, which can now be probed by all-sky time-domain surveys and radio pulsar timing arrays respectively. The main goal of B Massive is to combine theoretical astrophysics, radio an gravitational-wave astronomy and time-domain surveys, with state of the art data analysis techniques to: i) observationally prove the existence of massive black hole binaries, ii) understand and constrain their astrophysics and dynamics, iii) enable and bring closer in time the direct detection of gravitational waves with pulsar timing arrays.
By seeking its goals, the Action made a decisive contribution to one of the most important scientific breakthrough of the decade: the first detection of a low frequency gravitational wave signal with pulsar timing arrays. This was achieved within the European PTA (EPTA) collaboration, in which the B Massive project is framed. This marks the opening of a new observational window on the universe, widening the gravitational wave spectrum that has been already probed in the kiloHz range by the ground based interferometers LIGO and Virgo. Although the origin of this signal cannot yet be firmly established observationally, its properties match our theoretical expectation. In fact, this is exactly the type of signal we would expect to see if a cosmic population of massive black hole binaries were to emit low frequency gravitational waves. The interpretation framework developed within the Action allowed us to infer from the signal the main characteristics of this cosmic populations, confirming that massive black hole binaries do indeed exist, and efficiently emit gravitational waves.
The impact of this discovery has profound implications both for the scientific community and for the society at large. In fact, although fairly abstract theoretical objects, the impact of massive black hole binaries on our society cannot be underestimated. Black holes are among the most iconic physical objects, teasing the imagination and inspiring people of all ages and socio-economic backgrounds. The discovery of this signal made headlines all around the world contributing to the engagement of the public with science.Moreover massive black hole binaries are the main driver of future space borne observatories like the Laser Interferometer Space Antenna (LISA), an ESA-led endeavor to observe gravitational waves in space which will have a huge economic and technological impact for the European Union. The detection of this signal give us more confidence that the sources that LISA is targeting are out there awaiting discovery, to unveil the deepest secrets of the universe.
We can both see and listen to massive black hole binaries. Remarkably, besides arguably being among the brightest objects shining in the Cosmos, they are also the loudest gravitational wave sources in the Universe. As such, we shall take advantage of both the type of messengers – photons and gravitons – they are sending to us, which can now be probed by all-sky time-domain surveys and radio pulsar timing arrays respectively. The main goal of B Massive is to combine theoretical astrophysics, radio an gravitational-wave astronomy and time-domain surveys, with state of the art data analysis techniques to: i) observationally prove the existence of massive black hole binaries, ii) understand and constrain their astrophysics and dynamics, iii) enable and bring closer in time the direct detection of gravitational waves with pulsar timing arrays.
By seeking its goals, the Action made a decisive contribution to one of the most important scientific breakthrough of the decade: the first detection of a low frequency gravitational wave signal with pulsar timing arrays. This was achieved within the European PTA (EPTA) collaboration, in which the B Massive project is framed. This marks the opening of a new observational window on the universe, widening the gravitational wave spectrum that has been already probed in the kiloHz range by the ground based interferometers LIGO and Virgo. Although the origin of this signal cannot yet be firmly established observationally, its properties match our theoretical expectation. In fact, this is exactly the type of signal we would expect to see if a cosmic population of massive black hole binaries were to emit low frequency gravitational waves. The interpretation framework developed within the Action allowed us to infer from the signal the main characteristics of this cosmic populations, confirming that massive black hole binaries do indeed exist, and efficiently emit gravitational waves.
The impact of this discovery has profound implications both for the scientific community and for the society at large. In fact, although fairly abstract theoretical objects, the impact of massive black hole binaries on our society cannot be underestimated. Black holes are among the most iconic physical objects, teasing the imagination and inspiring people of all ages and socio-economic backgrounds. The discovery of this signal made headlines all around the world contributing to the engagement of the public with science.Moreover massive black hole binaries are the main driver of future space borne observatories like the Laser Interferometer Space Antenna (LISA), an ESA-led endeavor to observe gravitational waves in space which will have a huge economic and technological impact for the European Union. The detection of this signal give us more confidence that the sources that LISA is targeting are out there awaiting discovery, to unveil the deepest secrets of the universe.
Over its all duration the B Massive action made significant contribution to our understanding of massive black hole binaries both from the theoretical and the observational point of view.
The main results of the actions can be summarized as follows:
1-First evidence of a nanoHz gravitational wave signal in PTA data. B Massive played a key role in the assembly of the dataset and of the data analysis pipelines that led to the detection
2-Interpretation of the signal. We assessed the implications of the observed signal both for astrophysical and cosmological physical processes. We established that an astrophysical nature of the signal, would imply a MBHB population at the upper end of current observational estimates, in line with recent JWST observations and with profound consequences for our understanding of cosmic structure formation.
3-Implementation of the most up to date semianalytic model to evolve galaxies and massive black holes and for interpreting current and future gravitational waves and electromagnetic observations
4-Modelization of quasi periodic eruptions. Those are unexpected signals discovered around the start of the action that can be connected to a particular flavor of massive black hole binaries, and can be of paramount important to inform LISA and future gravitational wave detectors.
All these results were disseminated within the scientific community through a large number of refereed publications (more than 50), at conferences, symposia and colloquia. The wider general public was reached via several press releases, and extensive media coverage, especially related to the discovery of the low frequency gravitational wave signal, that was covered in hundreds of newspaper articles mentioning B Massive(just considering Italy), by an ERC interview and podcast and by two interviews to the PI aired on national television.
The main results of the actions can be summarized as follows:
1-First evidence of a nanoHz gravitational wave signal in PTA data. B Massive played a key role in the assembly of the dataset and of the data analysis pipelines that led to the detection
2-Interpretation of the signal. We assessed the implications of the observed signal both for astrophysical and cosmological physical processes. We established that an astrophysical nature of the signal, would imply a MBHB population at the upper end of current observational estimates, in line with recent JWST observations and with profound consequences for our understanding of cosmic structure formation.
3-Implementation of the most up to date semianalytic model to evolve galaxies and massive black holes and for interpreting current and future gravitational waves and electromagnetic observations
4-Modelization of quasi periodic eruptions. Those are unexpected signals discovered around the start of the action that can be connected to a particular flavor of massive black hole binaries, and can be of paramount important to inform LISA and future gravitational wave detectors.
All these results were disseminated within the scientific community through a large number of refereed publications (more than 50), at conferences, symposia and colloquia. The wider general public was reached via several press releases, and extensive media coverage, especially related to the discovery of the low frequency gravitational wave signal, that was covered in hundreds of newspaper articles mentioning B Massive(just considering Italy), by an ERC interview and podcast and by two interviews to the PI aired on national television.
The Action helped in making significant progress beyond the state of the art, mainly thanks to its critical contribution to the EPTA endeavor. Per se, the first detection of a nanoHz gravitational wave signal by PTA is certainly one of the major scientific breakthroughs of the decade. This marks the opening of a new observational window in the gravitational wave spectrum and the opening new observational windows on the universe has always brought new information and has significantly advanced our knowledge. Aiming at interpreting the PTA signal, we have performed the first exploration of the gravitational wave signal produced by massive black hole binaries in the PTA band within the framework of a fully self-consistent semianalytic model (SAM), taking into account all observational constraints coming from the observed galaxy and quasar mass and luminosity functions. Using this model we demonstrated that the detected PTA signal is consistent with an astrophysical origin, but its strength provides important constraints to the evolution of the cosmic population of massive binaries.