Understanding the Multi-scale Universe

In this STFC consolidated grant proposal, we present seven projects that address the following STFC roadmap key science questions:

A:4. When were the first stars, black holes and galaxies born? [P1,3,4]
A:5. How do galaxies evolve? [P6,7]
A:6. How are stars born and how do they evolve? [P3,4]
C:4. What is the nature of dark matter? [P2,5]
D:2. How can high energy particles and gravitational waves tell us about the extreme universe? [P1]

In P1, we study the coalescence of supermassive black holes in galactic centres. These are an important source of low frequency gravitational waves that are so energetic that they can be seen right back to the beginning of the Universe. We will calculate the expected frequency of such mergers, making predictions for the currently-running Pulsar Timing Array (PTA) and the planned LISA satellite. This "background" signal must be carefully understood in order for the the PTA to detect gravitational waves.

In P2 and P5, we probe the nature of dark matter. Dark matter is an invisible substance that appears to make up most of the mass of the Universe, yet it remains mysterious. In P2, we exploit a new technique for measuring the distribution of dark matter at the centres of tiny "dwarf" galaxies. We will use these new measurements to tightly constrain "Self-Interacting" and "Wave-like" dark matter models, and hunt for evidence of "dark matter heating". In P5, we study the effect of tiny clumps of dark matter on stellar streams that orbit the Milky Way. These streams form as globular star clusters are torn apart by gravitational tidal forces. By measuring the impact of tiny clumps of dark matter on these streams, we can measure the "granularity" of our Milky Way's dark matter halo. This allows us to directly measure the "temperature" of dark matter.

In P3, we study the origin of the abundance anomalies in globular clusters (GCs). Long thought to be simple, we now know that GCs show evidence of multiple populations of stars with peculiar chemical enrichment. We will test a new model whereby this peculiar chemistry is generated by the formation of a super-massive star (SMS) via stellar collisions. This new model has the potential to explain all of the puzzling data. We will also make predictions for upcoming surveys. This new formation model for SMSs may also shed light on the formation of supermassive black hole seeds in the early Universe.

In P4, we build the first stellar population models of the most massive stars, including their binary interactions. Current models used throughout the astronomy community become very inaccurate above ~100 solar masses. This project will dramatically improve stellar population models up to 1000 solar mass stars. This will provide new and improved energy and chemical yields, important for understanding both star and galaxy formation, and new estimates of the formation rates of black hole binaries. We will make these models publicly available to the community.

In P6, we will measure the chemical abundances of >4,200 red giant branch stars in the nearby Andromeda galaxy, for the first time. This exciting new data set - that we will make available to the community - will allow us to pin down the past history of Andromeda. This will provide a valuable counterpart to similarly detailed studies of our own Galaxy that are ongoing.

Finally, in P7 we will use new data from the SMASH, MAGIC and Gaia surveys to build a comprehensive map of two of our nearest satellite companions: the Large and Small Magellanic Clouds. This map - that we will make publicly available - will allow us to determine the masses and interaction history of the Clouds; to probe how star formation proceeds in the extreme environment of a galactic merger; and to study the elusive hot gaseous corona of the Milky Way.

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

1. Economic impact
- We will work with our research & enterprise support team (RES) to explore opportunities for commercially exploiting new software algorithms and advances generated over the lifetime of the grant.
- 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.
- We will organise an interdisciplinary workshop with our South East Physics Network (SEPnet) partners and RES on "Model Fitting". We will determine if methods developed in-house to cope with massive astronomical data sets like Gaia can find application in chemistry, engineering and/or financial modelling. Similarly, we hope to learn from modellers in these disciplines.

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; on the open access arXiv e-Print server; and on our Surrey Research Insight open access repository.
- Presenting our work at national and international conferences and workshops, writing press releases where appropriate.
- Making publicly available all of our software and, where possible, our simulation data products.
- Setting up a dedicated website for public engagement where we will make high resolution images and movies of our simulations publicly available.
- Promoting science results produced on this grant at our monthly public engagement events.
- Working with the physics department's outreach officer - Dr. Heather Campbell - to participate in major outreach initiatives across the country like the Royal Society Summer Science Exhibition and the Big Bang Fair.
- Working with Dr. Campbell 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 the SEPnet 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.