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 )
MEMBERSHIP SUBSCRIPTIONS
The following subscriptions are due at the beginning of each calendar year : Full Membership : £ 25 Reduced Rate : £ 15 First Year Membership : £ 10 Institution Membership : £ 25
The reduced rate is applicable to junior members of 17 years of age or less , full-time students , registered disabled , senior citizens over 65 years and members who are unemployed when subscription is due . The institution rate is applicable for groups or schools and includes membership for one adult and 15 juniors .
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 .