Thu, 29. March 2012
Astro-Speaker Watch - March 2012
Following his visit to MAS last year, when he gave an inspirational talk about globular clusters, there was a consensus amongst many members that we should invite Les back. Les has an encyclopaedic knowledge of astronomy and is currently doing a degree course in astronomy at Swinburne University. I wonder what the professors make of him, as he almost certainly knows more about observational astronomy than they do!
Les gave us a pretty fast-moving presentation about “The observational history and present state of knowledge as it relates to the major members of the Centaurus A/M83 cluster of galaxies”. Les informed us that this cluster is the second closest galaxy cluster outside our Local Group, the closest being the Sculptor Group. The cluster is located mainly in Hydra & Centaurus and is believed to be approximately 20 million light years distant - although some reports put it at only 12-14 million. It is bigger than the Local Group and contains seven times the mass of the Milky Way. It contains one giant lenticular galaxy (Centaurus A), three giant spiral galaxies, two medium spiral galaxies and the rest are mainly dwarf galaxies.
NGC 4945 (in Centaurus) is an edge-on spiral galaxy, discovered by James Dunlop at Parramatta, with star-burst activity and a Seyfert nucleus emitting the spectral emissions of highly ionised gas. Jets have been observed at x-ray wavelengths, evidence of a black hole at it's centre.
M83 (Hydra) is the third most massive galaxy in the group. It is also a star-burst galaxy, which means it is undergoing an unsustainably high rate of star formation (possibly due to a recent galactic collision). It has forty-five massive star clusters within four hundred light years of it's centre. It also has a high population of Wolf-Rayet stars, possibly around two thousand. (The Milky Way has less than five hundred of these objects, which are hot, high mass stars rapidly shedding material). Multiple stacked images by David Malin show diffuse galactic arms extending well outside the normally perceived limits of the galaxy.
NGC 5253 (Centaurus) is an irregular galaxy similar in size to our own LMC. It is believed to have had a recent encounter with M83 and is a star-burst galaxy. NGC 5068 (Virgo) is a mid-sized face-on barred spiral resembling the Milky Way.
NGC 5102 (Centaurus) is a peculiar galaxy, the second closest lenticular galaxy to us, consisting of a high population of very young stars. It's deficit of globular clusters is attributed to interactions with larger galaxies.
ESO 274-1 (Lupus) is a faint and obscure edge-on galaxy, barely visible in a 300mm telescope. It is twelve arc-minutes long. The Circinus Galaxy (Circinus) is a massive galaxy in the galactic plane, discovered by the UK Schmidt telescope at the AAO. It is difficult to observe - due to it's location in the Milky Way - but not impossible. It also has a Seyfert 2 type nucleus and x-ray jets.
Centaurus A (NGC 5128) is well known to amateur astronomers in the Southern Hemisphere as a favourite target and is probably the most distant galaxy visible to the naked eye. It also was discovered by Dunlop at Parramatta and is a peculiar galaxy with high radio emission. It is the most massive galaxy in the group, containing a whopping sixty per cent of the mass. It's small nucleus is Seyfert and it's huge dark dust band may be the result of a galactic merger in process.
ESO 270-17 is a “shredded” galaxy close to Centaurus A and is slightly larger than our own LMC.
NGC 5237 (Centaurus) is a small dwarf galaxy close to Centaurus A and is probably two galaxies in the same line of sight.
All in all, this was a great talk by Les Dalrymple, an amateur astronomer with a deservedly high reputation for topic accuracy. It should inspire further research by members and maybe an effort by our observers to view some of the objects which form the Centaurus A /M83 Group. Who will be the first MAS observer to spot the elusive Circinus galaxy?
Logged in members can find an audio recording of Les Dalrymple's presentation at http://www.macastro.org.au/home/index.php?option=com_content&view=article&id=188&Itemid=242
(This article has been submitted for publishing in the April edition of Prime Focus magazine, the monthly Journal of Macarthur Astronomical Society.)