Cosmic Impact of Massive Stars: Convective Mixing and Mass Loss
Lead Research Organisation:
Keele University
Department Name: Faculty of Natural Sciences
Abstract
The aim of this Consortium proposal is to improve numerical calculations of the most
massive stars in the Universe. Massive stars play a key role through the light they shine
and the chemical elements they produce. At the end of their lives, their cores collapse
into black holes which, because their gravities are so huge, even light cannot escape from.
The lives of massive stars and the related chemistry relate to several key STFC roadmap
questions. ``Question A: How did the universe begin and how is it evolving?'': Stars can
be used to probe the Universe and its evolution from its infancy, and indeed, the first
stars formed only 400 million years after the Big Bang. Even if most of those stars are
long dead, their chemical fingerprints are stored in long-lived low-mass extremely
metal-poor stars that survive today.
Comparing our models to observations of these metal-poor stars provides information about
the properties of the first stars and galaxies (question A4) and, more generally, this
proposal addresses key questions A5 and A6: ``How do galaxies and stars evolve?''.
Stellar models are also used as a theoretical framework for the interpretation of large
observational surveys, such as the VLT-Flames survey of massive stars, and to study as-yet
unexplained observations. For example, our models weighed the most massive stars discovered
to date, and the masses determined (up to 320 solar masses at birth) drastically upset
the previous upper mass limit of stars.
Furthermore, our stellar models will be the main input for supernova simulations. Thus
this project also addresses the question: ``D: How can we explore and understand the
extremes of the universe?''. Stellar models also provide input for the recently
opened window of gravitational waves (``D2: gravitational waves properties'') by
constraining the masses of gravitational-wave emitting "heavy" black holes. Mass loss is
a key process that determines the final mass of massive stars as they lose more than
half of their initial constituents via powerful stellar winds.
Stellar models provide a crucial theoretical framework for interpretation of data from
experimental and observational facilities representing billions of pounds of investments.
Theory, however, is lagging behind progress on the observational/experimental side, limiting
scientific progress. The stellar models developed in our proposal will provide a crucially
needed improved theoretical framework for interpretation of STFC-funded facilities,
will make use of STFC's computing facilities, and connect them to STFC-supported nuclear
physics facilities. Our work will thus maximise returns on STFC investment.
In this proposal we focus on the two key processes, the uncertainty of which is
crippling the predictive power of stellar models, for which great progress can be
made in the next three years and for which we have world-leading expertise:
mixing (Project A: PI Hirschi) and mass loss (Project B: PI Vink). We request 2 PDRAs
distributed across the two projects, each improving the treatment of a key process in
massive-star models. With the improved treatment of mixing and mass loss, we will
improve predictions of the cosmic impact of massive stars. In particular we will make
predictions concerning hot topics such as final masses of very massive stars linked to
gravitational wave emission, compactness of supernova progenitors and the possibility of
pre-explosive activity. The improved treatments will be implemented in an open-source stellar
modelling code and are likely to become the new standards for mixing and mass loss in
massive stars, with wide ranging applications and impact in astrophysics.
massive stars in the Universe. Massive stars play a key role through the light they shine
and the chemical elements they produce. At the end of their lives, their cores collapse
into black holes which, because their gravities are so huge, even light cannot escape from.
The lives of massive stars and the related chemistry relate to several key STFC roadmap
questions. ``Question A: How did the universe begin and how is it evolving?'': Stars can
be used to probe the Universe and its evolution from its infancy, and indeed, the first
stars formed only 400 million years after the Big Bang. Even if most of those stars are
long dead, their chemical fingerprints are stored in long-lived low-mass extremely
metal-poor stars that survive today.
Comparing our models to observations of these metal-poor stars provides information about
the properties of the first stars and galaxies (question A4) and, more generally, this
proposal addresses key questions A5 and A6: ``How do galaxies and stars evolve?''.
Stellar models are also used as a theoretical framework for the interpretation of large
observational surveys, such as the VLT-Flames survey of massive stars, and to study as-yet
unexplained observations. For example, our models weighed the most massive stars discovered
to date, and the masses determined (up to 320 solar masses at birth) drastically upset
the previous upper mass limit of stars.
Furthermore, our stellar models will be the main input for supernova simulations. Thus
this project also addresses the question: ``D: How can we explore and understand the
extremes of the universe?''. Stellar models also provide input for the recently
opened window of gravitational waves (``D2: gravitational waves properties'') by
constraining the masses of gravitational-wave emitting "heavy" black holes. Mass loss is
a key process that determines the final mass of massive stars as they lose more than
half of their initial constituents via powerful stellar winds.
Stellar models provide a crucial theoretical framework for interpretation of data from
experimental and observational facilities representing billions of pounds of investments.
Theory, however, is lagging behind progress on the observational/experimental side, limiting
scientific progress. The stellar models developed in our proposal will provide a crucially
needed improved theoretical framework for interpretation of STFC-funded facilities,
will make use of STFC's computing facilities, and connect them to STFC-supported nuclear
physics facilities. Our work will thus maximise returns on STFC investment.
In this proposal we focus on the two key processes, the uncertainty of which is
crippling the predictive power of stellar models, for which great progress can be
made in the next three years and for which we have world-leading expertise:
mixing (Project A: PI Hirschi) and mass loss (Project B: PI Vink). We request 2 PDRAs
distributed across the two projects, each improving the treatment of a key process in
massive-star models. With the improved treatment of mixing and mass loss, we will
improve predictions of the cosmic impact of massive stars. In particular we will make
predictions concerning hot topics such as final masses of very massive stars linked to
gravitational wave emission, compactness of supernova progenitors and the possibility of
pre-explosive activity. The improved treatments will be implemented in an open-source stellar
modelling code and are likely to become the new standards for mixing and mass loss in
massive stars, with wide ranging applications and impact in astrophysics.
Planned Impact
The members of our cosmic impact of massive stars (CIMS) consortium and their groups have strong track records in delivering impact through industrial engagement, education and outreach.
CIMS members and their groups have highly productive collaborations with industrial partners in a variety of fields, ranging from computer technology, through medical imaging to homeland security and nuclear energy. Moreover, the multi-disciplinary nature of our CIMS consortium affords our students and PDRAs broadened training opportunities. They will benefit from our industrial links, particularly in software optimisation alongside experts at Numascale. Designing and optimising advanced simulation codes, and Big Data mining as required by our massive datasets, are aligned with UK economic needs, so this training ensures the marketability of our students in diverse career paths.
Our CIMS Consortium is cognisant of its role in inspiring and training the next generation of scientists responsible for ensuring the UK's international competitiveness in both the academic and industrial sectors, so our outreach and public engagement activities are a key aspect of our mission. Our investigators and their institutes undertake a spectrum of
activities. With CIMS science spanning scales from the very small (nuclei) to the very large (stellar scale and beyond), and utilising state-of-the-art technology, from large scale high-performance computing facilities to generate evolving simulations of astronomical objects like stars (Project A), to international accelerator facilities such as CERN to study nuclear reaction rates, our consortium has a unique opportunity to capture the imagination of non-scientists.
CIMS will bring a greater breadth and depth to these activities through its interdisciplinary composition, and will add value through dedicated "Impact" sessions which will be scheduled as part of our regular consortium meetings, promoting best-practice in our efforts to maximise impact and facilitate knowledge exchange between the institutes and, in a wider context, with stakeholders and the general public.
A more detailed explanation of our impact capacity and plans is outlined in the attached "pathways to impact" document.
CIMS members and their groups have highly productive collaborations with industrial partners in a variety of fields, ranging from computer technology, through medical imaging to homeland security and nuclear energy. Moreover, the multi-disciplinary nature of our CIMS consortium affords our students and PDRAs broadened training opportunities. They will benefit from our industrial links, particularly in software optimisation alongside experts at Numascale. Designing and optimising advanced simulation codes, and Big Data mining as required by our massive datasets, are aligned with UK economic needs, so this training ensures the marketability of our students in diverse career paths.
Our CIMS Consortium is cognisant of its role in inspiring and training the next generation of scientists responsible for ensuring the UK's international competitiveness in both the academic and industrial sectors, so our outreach and public engagement activities are a key aspect of our mission. Our investigators and their institutes undertake a spectrum of
activities. With CIMS science spanning scales from the very small (nuclei) to the very large (stellar scale and beyond), and utilising state-of-the-art technology, from large scale high-performance computing facilities to generate evolving simulations of astronomical objects like stars (Project A), to international accelerator facilities such as CERN to study nuclear reaction rates, our consortium has a unique opportunity to capture the imagination of non-scientists.
CIMS will bring a greater breadth and depth to these activities through its interdisciplinary composition, and will add value through dedicated "Impact" sessions which will be scheduled as part of our regular consortium meetings, promoting best-practice in our efforts to maximise impact and facilitate knowledge exchange between the institutes and, in a wider context, with stakeholders and the general public.
A more detailed explanation of our impact capacity and plans is outlined in the attached "pathways to impact" document.
Publications
Arnett W
(2019)
3D Simulations and MLT. I. Renzini's Critique
in The Astrophysical Journal
Rizzuti F
(2021)
Constraints on stellar rotation from the evolution of Sr and Ba in the Galactic halo
in Monthly Notices of the Royal Astronomical Society
Scott L
(2021)
Convective core entrainment in 1D main-sequence stellar models
in Monthly Notices of the Royal Astronomical Society
Martinet S
(2021)
Convective core sizes in rotating massive stars I. Constraints from solar metallicity OB field stars
in Astronomy & Astrophysics
Cristini A
(2019)
Dependence of convective boundary mixing on boundary properties and turbulence strength
in Monthly Notices of the Royal Astronomical Society
Andrassy R
(2022)
Dynamics in a stellar convective layer and at its boundary: Comparison of five 3D hydrodynamics codes
in Astronomy & Astrophysics
Higgins E
(2021)
Evolution of Wolf-Rayet stars as black hole progenitors
in Monthly Notices of the Royal Astronomical Society
Belczynski K
(2020)
Evolutionary roads leading to low effective spins, high black hole masses, and O1/O2 rates for LIGO/Virgo binary black holes
in Astronomy & Astrophysics
Murphy L
(2021)
Grids of stellar models with rotation - V. Models from 1.7 to 120 M? at zero metallicity
in Monthly Notices of the Royal Astronomical Society
Groh J
(2019)
Grids of stellar models with rotation IV. Models from 1.7 to 120 M ? at a metallicity Z = 0.0004
in Astronomy & Astrophysics
Description | One major finding was achieved by running high-resolution multi-dimensional hydrodynamic simulations of the interior of massive stars (https://dx.doi.org/10.1093/mnras/stz312). These detailed simulations show that convection leads to more mixing than previously thought. These results were then included in new long-term one-dimensional (spherically symmetric) models of stars to investigate the impact of these new results (https://dx.doi.org/10.1093/mnras/stab752). Another key finding is the much stronger ejection of hydrogen burning products like nitrogen and aluminium thanks to the inclusion of updated mass loss theoretical prescriptions due to radiation-driven stellar winds (https://dx.doi.org/10.1093/mnras/stab752) building upon the work undertaken during this award. Other findings include a better understanding of how the chemical composition of stars affects their evolution and fate (including the mass of the black holes massive stars produce). |
Exploitation Route | Our multi-D and 1D results are relevant and being used by the stellar evolution, supernovae, stellar remnant and gravitational wave astronomy communities. For example, our results were used to predict the initial masses of black holes (e.g. https://dx.doi.org/10.1093/mnrasl/slaa196 ; https://dx.doi.org/10.1051/0004-6361/201936528 ). |
Sectors | Aerospace Defence and Marine Education Other |
URL | https://dx.doi.org/10.1093/mnras/stab752 |
Description | Key questions for humanity are: "What are we made of?" Where do we come from? I regular give a talk entitled "What are you made of?" which includes the findings of my research as well as that of my collaborators. The link below is a recording of my talk delivered in the context of the Institute of Physics online seminar series during the covid pandemic. https://www.youtube.com/watch?v=L8FWXNc-XxM Other public engagement activities include talks in schools and events on science and faith. These public engagement activities made key contributions to widening access to higher education and enhancing the science capital. |
First Year Of Impact | 2020 |
Impact Types | Societal |
Description | (ChETEC-INFRA) - Chemical Elements as Tracers of the Evolution of the Cosmos - Infrastructures for Nuclear Astrophysics |
Amount | € 4,999,605 (EUR) |
Funding ID | 101008324 |
Organisation | European Commission |
Sector | Public |
Country | European Union (EU) |
Start | 04/2021 |
End | 04/2025 |
Description | BRIdging Disciplines of Galactic Chemical Evolution (BRIDGCE) Consortium 2021-2024 |
Amount | £388,556 (GBP) |
Funding ID | ST/V000543/1 |
Organisation | Science and Technologies Facilities Council (STFC) |
Sector | Public |
Country | United Kingdom |
Start | 03/2021 |
End | 03/2025 |
Description | Collaboration on mass loss and evolution of very massive stars |
Organisation | Armagh Observatory and Planetarium |
Department | Armagh Observatory |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | My contribution is modelling the evolution of very massive stars and training members of the research group of Dr Jorick Vink on the use of stellar evolution code GENEC. |
Collaborator Contribution | Dr Jorick Vink and his group at Armagh Observatory are studying the impact of mass loss on the evolution of very massive stars. Together, we are studying the impact of these new models on the fate of very massive stars, e.g. black hole mass distribution, pair-instability supernovae. |
Impact | Work in progress. Papers will be published in the future |
Start Year | 2018 |
Description | Institute of Physics online public seminar |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Public/other audiences |
Results and Impact | Public talk entitled "What stars are you made of?" hosted online by the Insitute of Physics and BSL interpreted. Live audience was around 50. 100+ views on Youtube since. |
Year(s) Of Engagement Activity | 2020 |
URL | https://www.youtube.com/watch?v=L8FWXNc-XxM |