Astrophysics at Oxford: 2010-2015

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Astrophysicists at Oxford are trying to determine six basic things about the Universe. (1) What is it made of? The Universe appears to be at the beginning of a period of accelerated expansion driven by some mysterious stuff known as 'dark energy'. Einstein had a theory for what this stuff is: he called it the Cosmological Constant. We will be testing his theory by measuring the apparent brightnesses of distant exploding stars (supernovae), by measuring the distortions of distant galaxies as light is bent by the gravity of more nearby galaxies, and by measuring the precise positions of about one million galaxies. (2) What is the history of Hydrogen in the Universe? Hydrogen - the most abundant element in the Universe - is the most important building material for making stars. Atoms of Hydrogen combine into molecules within dense clouds, and these clouds provide the nursery for the birth of new stars. We will be using giant new telescopes operating at millimetre and radio wavelengths to observe, and hence understand, this process throughout most of the history of the Universe. (3) What can we learn about how galaxies formed from galaxies observed at current times? We are involved in large observational programmes that can be viewed as 'archaeology' of nearby galaxies looking for clues of important events in their history, for example by finding fast-moving gas orbiting a dormant supermassive black hole. We also study the relation between stellar populations and dark matter by studying the orbits of stars within and beyond the optical light in a galaxy. (4) What can we learn about how galaxies formed from distant galaxies observed at earlier times? Because of the finite speed of light, distant galaxies are seen when the Universe, and the galaxies within it, were young, and often these galaxies are so dusty that they are only effectively studied using infrared and radio observations. We map out the large-scale distribution of galaxies in the distant Universe using a combination of wide-field imaging (taking pictures) and spectroscopy (spreading light out into its constituent colours). We study these systems as they form and evolve, sometimes in dramatic bursts of star formation associated with supermassive black holes. (5) When did the first galaxies form? The Hydrogen in the Universe formed atoms about 300,000 years after the Big Bang, but was largely re-ionized (converted back to protons and electrons) during the so-called Epoch of Reionization. We use giant ground-based telescopes and satellites (e.g. the Hubble Space Telescope) to study these first galaxies and determine whether it was radiation associated with the birth of these galaxies, or stars within them, that was responsible for the re-ionization. (6) How do black holes influence star and galaxy formation? Black holes grow by 'gobbling up' gas and stars in a process called accretion. This process seems commonly to yield outflows in the form of winds and jets, the latter capable of reaching speeds very close to the speed of light. We study these systems in our own galaxy and in distant galaxies to determine the physics of such 'feedback mechanisms' (growth of the black hole is halted, albeit temporarily, by outflows driven by processes associated with the black hole). Our aim is to understand the influence of (compact) black holes on the formation of stars, galaxies and clusters of galaxies on much large physical scales.