Monthly Meeting – Speaker Dr Chris Lintott

18th Mar 2013
“Galactic Archaeology: Understanding the Universe’s past by looking at the present” On Monday we were very lucky to have Dr Chris Lintott give a talk to the group. The main theme of his talk was learning about the past universe from studying the remnants that remain visible today, which he described as a sort of galactic archaology. He began by describing how the universe is expanding, with more distant objects moving further away than nearer ones. This relationship between distance and velocity is known as the Hubble constant. Of course as things move away, the Doppler effect causes the wavelength of the light these objects emit to lengthen. So visible light moves to the red end of the spectrum, and beyond, which is why many of the current batch of telescopes are designed to look in the infrared. The very oldest objects have accelerated away for so long that the ‘light’ as we receive it has a wavelength in the microwave part of the electromagnetic spectrum. Dr Lintott showed us the now famous CMB (Cosmic Microwave Background) map of the early universe. The CMB radiation seems to come from the whole sky, but when temperature differences of a fraction of a degree are colour coded, the image seems quite mottled, revealing the beginnings of some structure emerging out of the uniformity. He talked about the data from the Sloan Digital Sky Survey and the 2 Degree Field projects, which gives us a structure of the universe with images of galaxy clusters and super clusters. The areas of stringiness/clumpiness showed where local gravity between galaxies won the battle with Dark Energy, that force which is causing the universe to expand. The thing that is still a bit of a puzzle (apart from Dark Energy) is that this clumpiness appears to have been achieved in a much shorter time than the physics would predict was possible. There is a project under way to find an explanation as to why some galaxies no longer had much dust or star forming regions within them. It may be that the jets of material and radiation emitted from the central black holes have the effect of stopping or otherwise preventing new star formation. He talked about the distribution of galaxy types, where their ages were plotted against their mass. ‘Blue’ galaxies, ie those containing mostly younger stars, occupied thier own space at the bottom of the graph, while ‘red’ galaxies containing older stars were predominantly in the top half of the diagram. Dr Lintott explained that the graph showed that the more massive ‘red’ galaxies could only have been formed by merger of other old galaxies, and not directly by the aging of ‘blue’ ones. Finally, Dr Lintott presented a possible explanation for the Late Heavy Bombardment (LHB), a period when the many of the craters were formed. Usually in a solar system that is relatively established many of the rougue bits of rock would have been hoovered up long before by the presence of the planets, so the fact that the LHB should happen was puzzling, unless an event happened that disrupted the orbits of some Kuiper Belt Objects and sent them into the inner solar system. One possibility is that the outer planets were much closer to the sun than they are now, with the orbit of Uranus being outside that of Neptune. Over time, the relative periods of Jupiter and Saturn’s orbits caused them to line up in the same place on several occasions, and this ‘resonance’ produced a regular gravitational kick that perturbed the orbits of Neptune and Uranus causing them to swap places. This would have disrupted the nearer KBOs causing some of them to have much more elongated orbits, taking them within range of the inner planets. An animation of this idea is shown here. All in all a very enjoyable presentation, a few concepts explained very well indeed. By Oliver Stogdon
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