Planet Formation in Binary Stars

Lead Research Organisation: University of Cambridge
Department Name: Institute of Astronomy

Abstract

For many years, planets with twin suns, were objects of science fiction. We now know that not only do they exist, but there are millions of them in our Galaxy. Such planets must survive in complex environments, unusually irradiated and tidally perturbed by two stars. Their discovery was driven by a revolution in astronomy. With telescopes in space, such as Kepler and CoRoT, and on the ground, like the UK's SuperWASP, one thousand extra-solar planets (exoplanets) have been detected in the last decade. Latest estimates suggest there are tens of billions in the Milky Way - that is about ten planets for every person on the Earth! The next few years will see many more discoveries as new telescopes and space missions, for example the European project GAIA and the UK's Next-Generation Transit Survey, probe deeper into the Universe around us.

New discoveries in science lead to breakthroughs in our understanding of the fundamental behaviour of the Universe. The discovery of exoplanets is no exception. Before we found them planet formation theory relied on our Solar System, its eight planets, minor planets and asteroids. However, a good scientific theory of planet formation should reproduce the menagerie of exoplanets in our Galaxy. The properties of planets - masses, radii, compositions, orbital periods (year lengths) and number frequency - provide the clues which help us solve the mystery of planet formation. One thing we know for sure is that planets form in discs of material around stars. In our solar system, and in most stars, these discs are short-lived and so no longer exist except for inert debris outside the orbits of the planets. However there are star systems out there which form discs much later in their lives: these are discs in binary-star systems that form when matter flows from one star to another.

About half the stars in our Galaxy are in binary systems. The two stars in a binary are locked by gravity in orbit around one another. As stars age they become larger and, in many binary systems, they interact by transferring material from one to another. The mass transfer process is complex and some material can end up in discs both around the accreting star or around both the stars. Just as around young stars, planets can form in these discs. Indeed we know that planets form around binary stars because a dozen have already been observed by the Kepler satellite. However, we understand very little about how many planets actually do form this way, why they do, or what influence such planets have on the life of the stars to which they are intimately bound. Discs around binary stars are a unique astrophysical laboratory in which to investigate planetary formation and how it depends on the properties of the discs and the stars, such as their chemical composition. The aim of this project is to predict the numbers and properties of planets around binary stars and compare to what we see. In this way, theories of planet formation and binary stellar evolution will be refined or ruled out and we shall learn much more about the environment in which these planets exist. Our basic understanding of planet formation around stars will be greatly enhanced and we will be one step closer to explaining the mystery of how planets form and manage to survive in close proximity to stars.

Publications

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Boubert D (2017) Binary companions of nearby supernova remnants found with Gaia in Astronomy & Astrophysics

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Boubert D (2017) Hypervelocity runaways from the Large Magellanic Cloud in Monthly Notices of the Royal Astronomical Society

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Brogaard K. (2018) The blue straggler V106 in NGC 6791: a prototype progenitor of old single giants masquerading as young in Monthly Notices of the Royal Astronomical Society

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De Marco Orsola (2017) Dawes Review 6: The Impact of Companions on Stellar Evolution in Publications of the Astronomical Society of Australia

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De Marco Orsola (2016) Post-common envelope PN, fundamental or irrelevant? in ArXiv e-prints

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Izzard R (2018) Post-AGB Discs from Common-Envelope Evolution in Galaxies

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Izzard R (2018) Binary stars in the Galactic thick disc in Monthly Notices of the Royal Astronomical Society

Related Projects

Project Reference Relationship Related To Start End Award Value
ST/L003910/1 31/03/2015 24/09/2017 £384,794
ST/L003910/2 Transfer ST/L003910/1 25/09/2017 30/03/2020 £112,574
 
Description By making computer models of binary stars in the most ancient parts of our Galaxy, I have quantitatively shown that many of them are or were interacting binary stars. The combination of my state-of-the-art models and asteroseismological data from the Kepler mission allowed an estimate of the rate of interaction which is important to understand how binary stars evolve. A number of the stars seen by Kepler are have an anomalously high mass and I showed that binary stars naturally account for this and their odd surface chemistry. I also showed that many of these overmassive stars were once binary but are now merged into single stars.
Exploitation Route My result, that many chemically peculiar, overmassive stars come from binaries is required reading for people working in galactic stellar populations. Previously, these stars were thought to have come from elsewhere in the galaxy, but I have showed that this is not required. Similarly, because many of these stars seem to be single it was assumed that they were always single. Rather, these stars are natural binary-star evolution products. I make robust predictions which can be tested with the next set of missions.
Sectors Digital/Communication/Information Technologies (including Software),Other

 
Description member of Institute of Astronomy "Computing Users Committee" which advises on computing policy at the institute.
Geographic Reach Local/Municipal/Regional 
Policy Influence Type Participation in a advisory committee
Impact The advice I give is important to the committee, especially because I used to run the equivalent committee at my previous institute. It helps to streamline and improve the computing experience of more than 100 staff at the institute. The computing staff probably also like the fact that they can discuss technical matters with me given my large amount of previous experience in (academic) computing.
 
Description Blavatnik Postdoctoral Fellowship Programme (application with Avishai Gilkis)
Amount £60,000 (GBP)
Organisation British Council 
Sector Charity/Non Profit
Country United Kingdom
Start 10/2017 
End 09/2019
 
Description STFC consolidated grant
Amount £370,690 (GBP)
Funding ID ST/R000603/1 
Organisation Science and Technologies Facilities Council (STFC) 
Sector Academic/University
Country United Kingdom
Start 04/2018 
End 04/2021
 
Title binary_c version 2 release 
Description Version 2.0 of the binary_c stellar population and nucleosynthesis framework has been released. 
Type Of Material Computer model/algorithm 
Year Produced 2016 
Provided To Others? Yes  
Impact The latest version is up to 50% faster on multi-CPU architectures, and now has Python, C and (object-oriented) Perl interfaces. The evolution algorithm in the code has been greatly improved also. The number of users around the world has gone up, for example binary_c is now being used to model stellar populations for an upcoming NASA white paper. The code also has a new logo! 
URL http://www.ast.cam.ac.uk/~rgi/binary_c.html
 
Description Disc physics with KU Leuven 
Organisation University of Leuven
Country Belgium 
Sector Academic/University 
PI Contribution I am working with various members of the astrophysics dept. at KU Leuven. Prof. Hans Van Winckel is my main observational collaborator on circumbinary discs, directly relevant to this fellowship. Prof. Leen Decin and I are working on observational counterparts with ALMA, and possible future grant applications in that field. With Dr. Denise Keller I am working on planetary nebulae, the descendents of the systems I am studying in this fellowship.
Collaborator Contribution My collaborators in Leuven are the observational equivalent of my theory work, they observe post-AGB stars and other stars with circumbinary and circumstellar discs.
Impact Work in progress.
Start Year 2015
 
Description Gravitational wave and stellar merging rate estimates 
Organisation University of Bonn
Department Argelander Institute of Astronomy
Country Germany 
Sector Academic/University 
PI Contribution I helped with the scientific and technical work that has gone into the paper arXiv:1801.05433 (submitted to MNRAS).
Collaborator Contribution PhD student Matthias Kruckow and his supervisor Thomas Tauris, at my former institute at the University of Bonn, are the main grant holders. Through the PhD project they developed a stellar population code to calculate rates of gravitational wave events caused by black hole and neutron star merging.
Impact Paper arXiv:1801.05433 (submitted to MNRAS).
Start Year 2016
 
Description Massive stars and supernovae with UVA 
Organisation University of Amsterdam
Department Anton Pannekoek Institute for Astronomy
Country Netherlands 
Sector Academic/University 
PI Contribution I have provided the software (and scientific/ technical support) used by members of the research group of Selma de Mink in Amsterdam. I provide ideas and feedback. I have co-written a number of papers with this group, which in the last year resulted in a paper on core-collapse supernova delay times from binary stars (Zapartas et al.) which was based on work originally done by an exchange student of mine when I was a professor in Bonn. The collaboration has been ongoing since I met Selma de Mink, back in 2005. A follow-up paper is currently with referees. In 2017 the Zapartas paper was accepted, and I gave a talk in Dublin at a supernova meeting on the subject.
Collaborator Contribution I work mostly with the students in Amsterdam, in particular Manos Zapartas and Mathieu Renzo, who make models of stellar populations with my binary_c code. I benefit greatly from their novel ideas and their time in that they not only are users of my code, but they also provide updates and improvements, and report bugs thus improve the quality of the software and algorithms available to me. My estimate of the in kind cost of this work is likely rather low, but is approximately what I would have to pay a PhD student to do similar work.
Impact Recent paper: "Delay-time distribution of core-collapse supernovae with late events resulting from binary interaction" in Astronomy and Astrophysics (http://adsabs.harvard.edu/abs/2017arXiv170107032Z) Talk at supernova meeting at DIAS, Dublin, June 2017.
 
Title Window to the Stars 2 
Description Window To The Stars is a graphical user interface to the popular TWIN single/binary stellar evolution code, for novices, students and professional astrophysicists. I have developed it over the last decade. I have started work on Window to the Stars 2, an updated version of the above. It has been redesigned to be more powerful and allow the use of multiple stellar evolution codes concurrently, such as the TWIN code, my binary_c code, the Cambridge STARS code and the popular MESA code. It is work in progress and I do most of the work in my spare time, but the benefits are already clear to people here in Cambridge, especially the stellar evolution students. 
Type Of Technology Software 
Year Produced 2016 
Open Source License? Yes  
Impact The software now allows the use of multiple stellar evolution codes (e.g. TWIN, my binary_c code, the Cambridge STARS code and the popular MESA stellar evolution code). It will be used for the first time in our public outreach open day in March 2016. This software will be used by my postdoc Ghina Halabi as part of the STFC funded "2D stellar evolution" project. This software is being used by one of the institute's PhD students. 
URL http://www.ast.cam.ac.uk/~rgi/window.html
 
Title binary_c now on git at University of Surrey 
Description Binary_c is a state-of-the-art software framework for the evolution of single and binary stars, nucleosynthesis studies and stellar population calculations. 
Type Of Technology Software 
Year Produced 2018 
Impact binary_c has now been released on gitlab at the University of Surrey. 
URL https://gitlab.eps.surrey.ac.uk/ri0005/binary_c
 
Description Armagh observatory talk 2017 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Postgraduate students
Results and Impact Talk about my fellowship research on post-AGB discs.
Year(s) Of Engagement Activity 2017
 
Description Binary stars in the galactic thick disc 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Industry/Business
Results and Impact A talk at the Institute of Astronomy, Cambridge, on binary stars in the galactic thick disc, related to my 2018 paper on the subject.
Year(s) Of Engagement Activity 2017
 
Description Binary stars: stellar merger factories - open evening, Surrey astro 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact A talk on the recent gravitational wave discovery, and the binary-star origins of these events, at the University of Surrey stargazing night, December 2017. There was much discussion with the audience, who also liked to use my "Window to the Stars" software to make their own stars.
Year(s) Of Engagement Activity 2017
 
Description Discs around binary stars -- Cambridge planets day 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact Talk on discs in binary-star systems at the Cambridge Planets Day 2017.
Year(s) Of Engagement Activity 2017
 
Description Dissolution of massive binary stars 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact A talk describing my work on runaway stars made in massive binary stars, a collaboration with Boubert, Erkal, Evans (Cambridge/Surrey), and Zapartas, Renzo and de Mink (Amsterdam)
Year(s) Of Engagement Activity 2017
 
Description Gaia data release 1 workshop 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact I attended the data release 1 workshop to learn about how Gaia's data release and database functions, and to communicate my ideas for what we need from Gaia. While I didn't give a formal talk, there were many informal discussions regarding the needs of stellar evolution modellers in relation to the upcoming Gaia data releases.
Year(s) Of Engagement Activity 2016
 
Description Guest lectures on "Scientific Writing" at Uppsala University 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Postgraduate students
Results and Impact I maintained my interest in teaching scientific writing as a skill for graduate students.
This was also an opportunity to collaborate with colleagues in Uppsala - a collaboration which continues into an ERC application this year (working also with the Gaia/ESO group in Cambridge).
Year(s) Of Engagement Activity 2016
 
Description Guest speaker at Solarfest, Dunsink Observatory (Dublin) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact 100-150 people braved the rain for the Solarfest in Dunsink. I was a guest speaker, where I spoke about my research and gave a talk on "The Origin of the Elements". I spent the day talking to the public and had a lovely chat with my taxi driver who knew all about binary stars. A wasted talent!
Year(s) Of Engagement Activity 2016
URL https://www.dias.ie/2016/05/10/10th-12th-june-2016-solarfest-at-dunsink-observatory/
 
Description Institute of Astronomy open day 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact The annual insitute of astronomy open day attracts hundreds of people from the East Anglia region. I put on a display showing off my "Window to the Stars" software. This is like a "web browser for stellar modelling": it enables one to make models of stars with a graphical interface that is simple enough that even children can use it (and they use it very well!).

I also spent the day answering questions on general astronomy and astrophysics from the public. This was a most rewarding activity.
Year(s) Of Engagement Activity 2016
URL http://www.ast.cam.ac.uk/public/
 
Description Massive stars and their marriage - Kunming 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Postgraduate students
Results and Impact A talk about massive binary stars at Kunming Observatory, China. One direct outcome from this visit is that in 2018 we are setting up a student exchange year in Kunming, financed by Kunming Observatory.
Year(s) Of Engagement Activity 2017
 
Description Nucleosynthesis in PNe and discs in pre-PNE talk (Hong Kong) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Talk at "Asymmetric Planetary nebulae" meeting 2017, Hong Kong.
Year(s) Of Engagement Activity 2017
 
Description Post AGB discs - introductory talk at the University of Surrey 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Postgraduate students
Results and Impact A talk to introduce my research with my new colleagues at the University of Surrey.
Year(s) Of Engagement Activity 2017
 
Description Post-AGB discs around binary stars @ "The physics of evolved stars: the role of binarity" Nice 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact a talk on the work of my fellowship "The physics of evolved stars: the role of binarity" ... lots of useful discussion during the week there and after my talk, and possible future collaborations.
Year(s) Of Engagement Activity 2017
 
Description Public Astronomy Evening at Surrey University 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Ongoing Public Astronomy Evenings at Surrey University. I attend and demonstrate stellar evolution software, in particular my "Window to the Stars" and occasionally give a talk.
Year(s) Of Engagement Activity 2018
URL http://gostargazing.co.uk/events/public-astronomy-evening-surrey-university-2/
 
Description Public talk at Cambridge University Astronomical Society 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Undergraduate students
Results and Impact Talk to the Cambridge University Astronomical Society on "The Origin of the Elements". The society is primarily of undergraduates, but the general public also attend.
Year(s) Of Engagement Activity 2016
URL http://www.srcf.ucam.org/astronomy/posters/TermcardLent.pdf
 
Description Review talk: Binary population synthesis 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Review talk on binary-star population synthesis at ESO, Garching.
Year(s) Of Engagement Activity 2017
 
Description Stargazing Live 12 February 2018 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact I showcased my "Window to the Stars" software at this event which was packed out with public, school pupils, children, students and media. There were many useful discussions, one of which may lead to a summer studentship.
Year(s) Of Engagement Activity 2018
 
Description Talk at "Binary Stars in Cambridge" conference, also LOC/SOC member 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact I was LOC/SOC member, and a speaker, at the "Binary Stars in Cambridge" conference 2016. This was the most important conference in the field during 2016. My talk was on "Massive stars in the Galactic thick disc", a collaboration I have engaged with members of the GAIA/ESO team in Cambridge.
Year(s) Of Engagement Activity 2016
URL http://www.ast.cam.ac.uk/meetings/2016/binary.stars.cambridge.2016
 
Description Talk at Royal Astronomical Society meeting "Industrial revolution in Galactic astronomy" 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Extensive high precision surveys to obtain accurate chemical, kinematic and age information about stellar populations in the Milky Way, are a major investment of the astronomical community over the coming decade, and are on the verge of delivering long sought stellar properties for field and cluster stars. All of this on an industrial scale, ranging from several tens of thousands to a billion of stars.

The UK community is already playing a major role in the development of this synergy. This is the right time to gather together and discuss the potential systematic uncertainties plaguing such investigations, and establish a roadmap for the most effective exploitation of the large flow of data that will soon be available to the astronomical community.
Year(s) Of Engagement Activity 2016
URL https://sites.google.com/site/rasspecialistirga/home
 
Description Talk at annual BRIDGCE meeting, Keele University, September 2016 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact I spoke about my work on binary stars in the Galactic thick disc. This is related to chemical measurements in stars being done here in Cambridge and the asteroseismology being done in Birmingham, and stellar evolution work in general (hence the talk at the BRIDGCE meeting).
Year(s) Of Engagement Activity 2016
URL http://bridgce.ac.uk/bridgce/events/StarsSupernovaeNucleosynthesisIII--7-8-September-2016
 
Description Talk at the 12th Torino workshop on "Circumbinary discs around AGB stars" 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact I gave a talk on the first stage of my planet formation project: circumbinary disc formation, in particular in relation to post-AGB stars after common envelope evolution. I described the project in detail and obtained excellent feedback from esteemed colleagues. This led to a number of new ideas some of which have already been worked into the project.
The meeting also allowed me to meet with many of my colleagues who use by "binary_c" stellar population and nucleosynthesis code in preparation for the release of version 2.0 of the software. This was very useful indeed.
Year(s) Of Engagement Activity 2016
URL https://indico.cern.ch/event/456759/
 
Description Weekly public computer demonstrations as part of Insitute's public observing evenings 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Our institute holds weekly public observing events. To contribute to this I have set up a (semi-permanent) display highlighting my "Window to the Stars" software. This is like a web browser for stellar evolution modelling.

Especially on (all too frequent) rainy nights, my interactive stellar display provides an opportunity to communicate the wonderful world of stars with the general public. In particular, children love to be able to make their own stars on the computer. It is a very rewarding activity.
Year(s) Of Engagement Activity 2016
URL http://www.ast.cam.ac.uk/public/public_observing