Prof Phil James from the Astrophysics research Institute of the Liverpool John Moores, University was the guest speaker at the October meeting of Keighley Astronomical Society. He entertained a packed lecture theatre with his presentation on ‘Galaxies and Dark Matter’. The invisible stuff that only shows its presence by it’s gravitational pull. Without dark matter, a galaxies speedy stars would fly off in all directions. Prof James explained that in the 1930’s, astronomers made observations which tended to suggest that the orbits of stars in various galaxies did not have the expected relation between speed and distance from the galactic centre. It was not until 1975 that astronomer Vera Rubin showed that the speeds of stars in orbit in every galaxy tended to be independent of the distance from the centre of the galaxy. If the visible mass of the galaxy was responsible for star acceleration, then the speeds should vary with distance. It was quickly realised that almost all (90%) of the mass of galaxies reside in an invisible halo of unknown, individual partials sticking out into space for a distance about ten times the visable radius of the galaxy. Using the idea of ‘Gravitational lensing’ proposed by Einstein, astronomers have been able to map the distribution of dark matter over the near universe in the last thirty years.
Prof James said. “I would be pleased to pay a return visit to Keighley, I have enjoyed my time with the society members”.
Society member Michael Cummings summed up the thoughts of those present at the meeting by saying, “Thanks for a fascinating evening once again. Thanks to Prof James. It would be a pleasure to hear him speak again”.