NEBULA VOLUME 44 Issue 2 PAGE 4
Edwin Hubble convincingly showed in the 1920 ' s that the Universe was expanding and that on the largest scales everything was moving away from each other. However, at the same time, it was found that at smaller scales in the Universe, namely at the scale of Local Galaxy Clusters, this was not happening. Gravity, instead, reigned supreme and the result was galaxies coming together. As we all know, the two largest galaxies in our Local Group— Andromeda and the Milky Way— are on a collision course and will make contact in about 4 billion years.
I have always been interested in galaxy collisions and this interest was awakened by a recent article that I came across. There it was proposed that galaxy collisions were probably the principal way in which the many small protogalaxies in the early Universe became, by mergers, the normal galaxies that we observe today. Indeed the article stated that the Milky Way galaxy may have formed‘ from as many as 100 protogalaxies as a result of galactic mergers’. In addition we know that the Milky Way contin-
GALAXY MERGERS by Gerry Leake
ues to‘ eat’ small dwarf galaxies that approach too close, and that at the present moment the dwarf galaxy in Sagittarius is being pulled apart and will be absorbed into the Milky Way in the near future( astronomically speaking).
But‘ this is what galaxies do— they eat their friends if they get too close’, and this cannibalism can result in some of the largest and most energetic galaxies that we know of— the supergiant elliptical galaxies with massive black holes at their centres. These supergiant elliptical galaxies are often found at the centres of dense galaxy clusters, and this has enabled them to grow to such large sizes because of the closeness to the centre of such clusters of much‘ galaxy fuel’ to feed on. A well known example of such a supergalaxy is M87 in the constellation of Virgo. This has a black hole at its centre of 6.8 billion solar masses, which is over 1,000 times more massive than the black hole at the centre of the Milky Way. Whew!!
Colliding Spiral Galaxies of Arp 274 Credit: NASA, ESA, M. Livio( STScI) and the Hubble Heritage Team( STScI / AURA)
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Meetings programme 2016
Feb 10 Dr. Michael Martin-Smith( HERAS), Asteroids, armaggedon or Eldorado? Mar 9 Prof. Andreas Friese( Birmingham University), Shining a Light on Black Holes Apr 13 David Sellers( LAS), William Gascoigne of Leeds and the Renaissance of Astronomy May 11 Gareth Powell( Met Office. Exeter), Forecasting the impacts of space weather Jun 8 Dr. Katherine Johnston( Leeds University), Unravelling massive star birth with ALMA Jul 13 Tim Old( HERAS), New horizons, Pluto and beyond Aug No meeting Sep 14 Dr. Matthias Willbold( Manchester), The accretion of the Earth- Moon system Oct 12 Dr Ken Amor( Oxford University), Chelyabinsk meteor Nov 9 Prof. Sam Falle( Leeds University), Relativistic jets Dec 14 President’ s Evening
LEEDS ASTROMEET Saturday 12 th November 2016 Clothworkers’ Hall, Leeds University( doors open 9 a. m., start 10 a. m.) A whole day of Astronomical talks, exhibitions, slide show s and stalls.