The bright and the dark Universe - from bright stars to Dark Energy

Astronomy is a curious science. We have no traditional laboratories at our disposal, we cannot poke and prod our scientific subjects, nor can we setup carefully thought out experiments that will best test our scientific hypotheses. Our laboratory is the Universe - from nearby stars and planets to astronomically distant galaxies; our instruments are telescopes, gathering light of all wavelengths, pinpointing the position of shining stars, gas and galaxies. Our experiments are cleverly selected observations of these objects, translating their light into information about their composition, studying them at what we believe are different stages of their evolution, and observing their effect on neighbouring objects. We create our own experiments from the immensely chaotic master laboratory that is the Universe, and we take on the challenge that is to explain how it came to be, what it is made of, how it will end, and what fundamental laws tick the whole thing into motion.

We are good at this, consider some of what we have learned: that the Universe is around 13.7 billion years old and that it has since been expanding; that its expansion is seemingly accelerating; that the Universe is full of a delightful mix of galaxies of all sizes, shapes and colours; that galaxies are filled with stars, planets, gas and dust; and that the Universe seems filled with a mysterious unseen amount of matter that responds only one to the four fundamental forces of the Universe: gravity. As a scientist, however, my focus is firmly on things we do not yet know. Why is the expansion of the Universe accelerating (a phenomenon we call Dark Energy)? Is it being driven by a force previously unknown, or is the Universe's acceleration an illusion that stems from a potential lack of understanding of how gravity works? How come most of the matter of the Universe is unseen? How does this Dark Matter relate to the visible tip of the Universe's matter content, and how does it affect its evolution? And why such a variety of galaxies? Why some blue, red or green, and how do they relate to the unseen matter distribution of the Universe?

My personal contribution towards the monumental task that is answering these fundamental questions is to establish a robust link between the components of the Universe that are visible and those that are not. As an Ernest Rutherford Fellow I will begin by understanding how we can confidently interpret the light coming from galaxies in a way that tells us about their own growth and evolution, and then how to link it to the evolution of the dominating Dark Matter component of the Universe. I will do this by taking both models of stellar light and models of how structure grows in the Universe under the force of gravity and, for the first time, contrasting such models with observations and computer simulations in a self-consistent way. The result will be an increased knowledge of how certain types of galaxies relate to the Dark Matter, and in turn this knowledge will allow me to select the optimal set of observations to learn how structure formed in the Universe. This is a tough task, but I have shown in a preliminary analysis that the knowledge we gain provides a big step in understanding the behaviour of Dark Energy across cosmic times, and enhances our knowledge about gravity.

In other words, my research programme is an ambitious optimisation exercise. One that turns the limited observations we can make of the Universe into as powerful tool to investigate its fundamental laws as possible, whilst simultaneously learning about the beautiful part of the Universe that we are luck enough to observe - galaxies.