Astrophysics at Oxford

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Astrophysicists at Oxford are trying to determine three basic things about the Universe. What is it made of? The Universe now appears to be begun a period of accelerated expansion driven by some rather mysterious stuff known as `dark energy'. Einstein had a theory for what this stuff is, he called it the Cosmological Constant, and we will be testing his theory by measuring precisely the positions of about a million galaxies, the distortions of more distant galaxies due to the bending of light by gravity, and the brightnesses of distant supernovae. How did the galaxies form? It now looks like the disks of galaxies like the Milky Way have had a rather boring past history, growing by gradual accretion of both normal and `dark' matter and forming their stars gradually. Most of the stars in the Universe, however, are in so-called spheroidal galaxies which appear to have had a much more exciting history. They seemed to have formed in dramatic bursts of star formation associated with the growth of supermassive black holes. We can see if this is true by doing two very different sorts of `experiment': we can look directly at very distant galaxies which, because of the finite speed of light, are seen at times when the Universe, and the galaxies within it, were young; or we can do `archaeology' on nearby galaxies looking for clues of an exciting youth, for example by finding fast-moving gas orbiting a dormant supermassive black hole. How do exotic objects like quasars influence the Universe? When spheroidal galaxies were young and their black holes were still growing they seemed to develop jets that squirted material into their environments. This process heated up large parts of the Universe. Jets are also seen in our own Galaxy associated with so-called microquasars, and since the output from these objects varies on human timescales, they are easier to study, and should provide clues as to how jets work and how important they were in the history of galaxy formation.