Wed, 3. October 2012
Astro-Speaker Watch - September 2012
"Andromeda and the 30 Dwarfs" was the title of Professor Geraint Lewis's September talk to Macarthur Astronomical Society.
Image 2
Image 2 shows the outer suburbs of the Andromeda and Triangulum galaxies, as published in 'Nature'. They are located more than 2,500,000 light years away from us, and the dashed lines mark circles around Andromeda and Triangulum with diameters equivalent to approximately 900,000 light years and 300,000 light years, respectively.
The enhanced image shows faint structures that are the fossils from the formation of M31 and from subsequent encounters with other galaxies.
Many of these relics are recent discoveries by PandAS, and include various streams of stars, very small ("dwarf") galaxies, and a distortion around the disk of Triangulum which is evidence that it is strongly interacting with its more massive neighbour, M31.
Pictures of the disks of these galaxies, as they normally appear, are overlaid at their positions, and an image of the full moon is included (top left) for scale. The image has been stretched so as to show the faint structures more clearly. (The picture of the disk of Triangulum is credited to T. A. Rector).
These stars and dwarf galaxies consist of the remnants of galaxies that have collided with M31 and been ripped apart in the process. The debris is shown to extend in streams swirling around M31 at great distances and even as far as M33 and is the archaological record of the violent and destructive past of M31, as it devoured and destroyed any smaller galaxy which it encountered.
The PandAS survey, which is now stretching into its second decade, has found not only a halo of previously undetected stars but also around thirty faint dwarf companion galaxies around M31, stretching out half a million light years in radius. These are shown in Image 3.
For the record, astronomers have suspected for some time that our Milky Way and M31 are on a collision course. This year, they confirmed that a direct collision will occur in about four billion years time, with M33 also a likely participant.
This was another great talk by Geraint Lewis, who was making his fifth address to the Macarthur Astronomy Forum – a record!
Geraint Lewis Blogsite (recommended): http://cosmic-horizons.blogspot.com.au/
AT THE MACARTUR ASTRONOMY FORUM:
This month: Astronomer, Dr. Simon O'Toole.
November: Astronomer, Dr. Emil Lenc.
This article was written for publication in the October Edition of "Prime Focus" magazine - the journal of Macarthur Astronomical Society.