Multi-scale simulations of the Universe

Our new group at the University of Surrey has computational and dynamical expertise over a wide range of scales from the stars orbiting around Sag A*, to cosmological simulations of the Universe. By tying these different scales together for the first time, we seek to shed new light on key outstanding problems in modern astrophysics:

- How do massive black hole (BH) binaries merge? (p1);
- What is the nature of dark matter? (p2; p3);
- How do galaxies form? (p4);
- How do globular clusters form? (p5); and
- How do massive stars form? (p6)

At the same time, we will build a community simulation database to: (i) provide mock data for up-coming missions eLisa, Gaia, Alma, Euclid and SKA; and (ii) to guide our theoretical understanding of these new and exciting data.

In p1, we study the coalescence of supermassive BHs in galactic centres. While every massive galaxy appears to host a supermassive BH, a close binary pair of holes has never been seen. Understanding how and why such binaries merge is important for the formation and evolution of galactic bulges, and because such mergers produce gravitational waves that are visible across the entire Universe. In this project, we will study in detail the combined effect of four coalescence mechanisms - one of which is completely new - for the first time.

In p2 and p3, we probe the nature of dark matter. Dark matter is an invisible substance that appears to make up most of the gravitating mass of the Universe, yet it remains mysterious. In p2, we exploit a new numerical technique for modelling dark matter fluids to place new constraints on the "temperature" of dark matter. This will allow us to test or rule-out popular dark matter particle candidates like sterile neutrinos. In p3, we will measure the dark matter distribution in the smallest dwarf irregular galaxies for the first time. In such galaxies, there are so few stars that the dark matter is expected to be "pristine", untouched by the gravitational effects of strong stellar feedback. By combining data for gas and star motions in these systems, we will test our cosmological model, and probe the nature of dark matter, on the smallest scale to date.

In p4, we study star formation & feedback in a galactic context using state-of-the-art numerical methods. The key bottleneck in our understanding of galaxy formation is how stellar feedback, originating within giant molecular clouds (GMCs), couples to the larger scale galactic environment. In star formation, the key bottleneck is how, and in what initial state, turbulent GMCs form from galactic gas. We will solve both by using "zoom" simulations to model star formation in its galactic context, for the first time.

In p5, we study the formation of globular clusters (GCs). These have been known about since antiquity yet their formation mechanism remains elusive. Are they simply the massive end of clustered star formation? And if so, why do they show such a distinctive bi-modality in colour, age, metallicity and their spatial/kinematic distribution? We will use our state-of-the-art galaxy formation simulations - that resolve the most massive star forming regions - to construct a single unified model for GC formation, for the first time.

Finally, in p6 we look at what we can learn about star formation from the nearby "30 Doradus" complex in the Large Magellanic Cloud. This is home to many young massive O stars that will explode as supernova just a few million years from now. The birth sites of these massive stars are believed to be the cores of dense stars clusters. However, ~two thirds of them are found outside of stars clusters. Some of these are observed to be moving at great speed - so-called "runaway" stars. We will study how and why massive stars escape their parent clusters, and consider the implications of this both for star formation within 30 Doradus, and on the scale of the host galaxy.

Our STFC consolidated grant will be of great benefit to fellow academics (see Academic Beneficiaries). In addition, we will deliver economic and social impact, and knowledge transfer as follows:

1. Economic impact
- We will explore whether our in-house algorithms and/or special "boutique" hardware ideas can be commercialised by: (i) organising two interdisciplinary workshops with our South East Physics Network (SEPnet) partners on: "Multiscale modelling" and "Model fitting"; and (ii) working with our in-house research & enterprise support team (RES), and (where relevant) applying for money from the STFC and the Royal Society to further develop any commercial ideas.
- We will ensure that our PhD students and postdocs have the necessary skills, experience and contacts to move out of astrophysics if they wish to do so, providing a talent-stream for British industry. To achieve this, we will deliver relevant training through through RES and GRADnet.

2. Social impact
We will ensure that all scientific work output from our STFC consolidated grant is made freely available to be used by interested industry partners, schools and colleges, and/or the interested public. We will achieve this by:

- Publishing all of our work in high ranking, peer-reviewed, journals and on the open access arXiv e-Print server.
- Presenting our work at national and international conferences and workshops, writing press releases where appropriate.
- Making publicly available all of our simulation data products through a web interface for others to download and use.
- Making publicly available all of our software tools both for running our simulations, and analysing them.
- Setting up a dedicated website for public engagement where we will make high resolution images and movies of our simulations publicly available.
- Organising a monthly public engagement event during term time, showcasing our latest simulation results using a 3D theatre system, followed by (weather permitting) a chance to view the real night sky using existing in-house outreach facilities.
- Working with our outreach officer - Miss Sarah Barnes - to participate in major outreach initiatives across the country: National Astronomy Week; the Royal Society Summer Science Exhibition; and the Big Bang Fair.
- Working with our outreach officer to set up an "Astronomy Masterclass" - Simulating the Universe - aimed at first and second year sixth form students. This will (i) excite young students about physics and encourage University uptake in the subject; (ii) train young students in computer programming, a valuable transferrable skill; and (iii) promote our STFC funded research to enthusiastic physics students.

3. Knowledge transfer
We will facilitate knowledge exchange with industry, schools and the general public based on output from this STFC consolidated grant bid. To achieve this, we will:

- Work with RES to identify industry and academic partnerships that could be of mutual benefit.
- Work with our employer engagement officer - Mrs Kay Pearson - to seek industry partnerships for our PhD students.
- Offer graduate training across the new GRADnet SEPnet network to ensure that our PhD students have business-relevant data mining and computational skills.