The History of Merging Compact-Object Binaries

Project Information

HOMERICS

Grant agreement ID: 794393

DOI

10.3030/794393

Project terminated on 30 September 2020

EC signature date 16 March 2018

Start date 3 October 2018

End date 2 October 2021

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 244 269,00

EU contribution

€ 244 269,00

Coordinated by

UNIVERSITA DEGLI STUDI DI PADOVA
Italy

Periodic Reporting for period 1 - HOMERICS (The History of Merging Compact-Object Binaries)

Reporting period: 2018-10-03 to 2020-10-02

Summary of the context and overall objectives of the project

On February 11, 2016 the LIGO-Virgo scientific collaboration announced the detection of a gravitational-wave signal from two colliding black holes. The event was registered on September 14, 2015 and it was the first direct evidence that (i) black holes exist, (ii) black holes can merge and that (iii) stellar black holes can be as heavy as 40 times the mass of the Sun.

Since then, the LIGO-Virgo instruments detected gravitational-wave signals coming from tens of colliding black holes, and this number is destined to significantly increase in the next years.

Despite the increasing number of detections, from the theoretical point of view, the formation and evolutionary history of black holes are still unknown and we cannot provide an astrophysical interpretation to the systems detected by LIGO-Virgo. We know that stellar black holes form from the death of massive stars, but theoretical models that predict black hole masses are very uncertain. Furthermore, we do not know what are the mechanisms that bring two black holes so close to each other to make them collide.

The aim of the HOMERICS project is to shed light on the formation and evolutionary pathways of merging compact objects and the final goal is to provide an astrophysical interpretation for present and forthcoming gravitational-wave detections.

The first objective of the project is to study the evolution of isolated binary stars and investigate whether two stars that are bound to each other since the beginning of their life, can form LIGO-Virgo-like black-hole systems.

The second objective is to investigate whether LIGO-Virgo-like black-hole systems can form in a dense stellar environment, that is in a more crowded place, which can contain hundreds of thousands of stars (e.g. star cluster).

To achieve the objectives, a large number of computer simulations of isolated binaries and star clusters must be carried out. As such, the HOMERICS project requires the development of new codes (called SEVN and HiGPUs-RX). To extend our knowledge of merging black holes, the codes will be developed to run natively on state-of-the-art computing accelerators (Graphics Processing Units) and they will implement the most recent developments in stellar evolution and stellar dynamics theories.

Furthermore, all the simulations and codes developed for the HOMERICS project will be publicly available after the end of the project. This will allow other users to (i) reproduce the results of the project, (ii) (re)use the data and/or codes to investigate other astrophysical phenomena, not necessarily related to the HOMERICS project.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The activities of the first two years of the project focused mainly on the first objective (O1), marginally on the second objective (O2) of the action, and on the development of new parallel codes to treat stellar dynamics (work packages WP1, WP2, WP3 and WP4), in line with the original work plan described in the project.

To achieve objective O1, the researcher carried out a large set of simulations of isolated binary stars with an up-to-date version of the SEVN code, entirely developed by the researcher during the reporting period. The results of the runs were accurately analyzed (milestones M2.2 M2.3 M2.4 and M3.1).

The main scientific results have been presented in a first-author, peer-reviewed publication on Monthly Notices of the Royal Astronomical Society, Volume 485, Issue 1, May 2019. The paper makes predictions on detectable merging black-hole binaries and introduces an innovative formation channel for black holes with masses larger than 50 times the mass of the Sun.

The researcher also investigated the effect of stellar rotation on the formation of heavy black holes by using new stellar evolution prescriptions from the FRANEC code (milestones M1.1 and M1.2). This work led to an additional peer-reviewed publication, not scheduled in the original work plan: The Astrophysical Journal, Volume 888, Issue 2, article id. 76, 11 pp. (2020). The work shows that stellar rotation and collapse of the star's hydrogen envelope has a crucial impact on the black hole mass spectrum. This work also laid the foundations for a fruitful, long-lasting collaboration between the researcher, the beneficiary, and the FRANEC developers.

The objective O1 of the Marie Curie action has been fully achieved.

According to the original work plan, the researcher has also worked towards the objective O2. The researcher is currently finishing the development of the HiGPUs-RX code, the innovative code to treat stellar dynamics described in the action’s proposal (WP4). The original name of the code was HiGPUs-RX. This has been changed to the more meaningful ISTEDDAS, a word that means “STARS” in the Sardinian language. ISTEDDAS will be used after the second year of the fellowship to achieve the objective O2 by the end of the year 2021, as scheduled.

Besides the activities and deliverables scheduled in the original work plan, the results of the HOMERICS project have been furtherly disseminated and communicated. The researcher gave 1 individual, invited outreach talk on black holes and gravitational waves, he was invited to give 6 talks at international conferences (including one at the annual meeting of the American Astronomical Society), he co-authored more than 60 peer-reviewed scientific papers, he was part of the editorial team of the special-event Ligo-Virgo paper to present GW190814 (https://iopscience.iop.org/article/10.3847/2041-8213/ab960f) and he has been spokeperson for the first official LIGO-Virgo webinar to announce GW190814.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Not only the impact objectives of the HOMERICS project have been fully met, but the research conducted for the HOMERICS project has already exceeded the planned impact expectations, even 1 year before the end of the fellowship.

During the first two years of the fellowship, the researcher acquired many competencies, laid the foundations of many international, long-lasting collaborations, significantly increased his research network, and acquired crucial visibility in the field of gravitational-wave sources, above expectations.

The researcher has also been awarded a competitive prize (Premio Giovani Ricercatori, success rate < 3%, https://www.scienzainrete.it/premio) for the presentation of an innovative mechanism to form heavy black holes with a mass more than 50 times the mass of the Sun (results in MNRAS, Volume 485, Issue 1, May 2019). The innovative mechanism represents a crucial progress beyond the state-of-the-art for black-hole formation models, and it
provides a possible interpretation for the formation of GW190521, the LIGO-Virgo event with the heaviest black holes (announced on September 2, 2020).

The researcher also had the chance to re-enforce his teaching and mentoring skills through a course for PhD students on black holes dynamics at SISSA – Trieste and through the supervision of more than 5 international students.

Furthermore, the development of the HiGPUs-RX code and the open simulation data archive, towards the objective O2 of the project, will likely lead to a further increase of the impact of the HOMERICS project as well as to a further increase of the researcher’s visibility in the field of gravitational waves.

Finally, the results and codes of the HOMERICS project will be exploited for several years, therefore their impact will extend significantly beyond the end of the fellowship.

That's just me (August 2020)

The black curve shows that heavy black holes (> 100 times the mass of the Sun) can form!