18 June 2002
Galaxy Shredding: caught in the act
Initial images from the Hubble Space Telescope's latest state of the art camera have captured perhaps the clearest example yet of a galaxy in the process of being literally torn apart by its bigger neighbour.
This process, dubbed `shredding', removes stars from the outer parts of a small galaxy due to its gravitational interaction with a larger galaxy. Astronomers from Swinburne University of Technology and The University of New South Wales made this remarkable discovery when NASA released the first images from the recently installed Advanced Camera for Surveys (ACS).
With a keen eye, Associate Professor Duncan Forbes and Dr Michael Beasley noticed an interesting background galaxy in last month's publicity image of the `Tadpole' galaxy taken by the new ACS and highlighted in newspapers and astronomy magazines worldwide.
"Although a similar disruption process is thought to be at work in our galaxy, the Milky Way, and our sister galaxy, Andromeda, this is the first time we have clear evidence of stars currently being shredded from the dwarf galaxy," Forbes said.
Adding "In the images the galaxy appears as a bright dot, located close in projection to a highly inclined spiral. If one looks carefully a plume of material can be seen extending from two opposite sides of the small galaxy."
After using image enhancement techniques to better reveal the plume, it reminded Forbes and Beasley of the simulations carried out by their colleague Dr Kenji Bekki, which reveal a small galaxy being disrupted or `shredded' as it orbited around a larger galaxy
"A dwarf galaxy can lose a significant fraction of its stars due to the gravitational interaction with the dark matter surrounding a large galaxy. These shredded stars can be seen as spectacular tidal tails. Tidal tails are significant to astronomers as they trace out the dwarf galaxy's past and future orbit." Noted Dr Bekki.
The interacting system captured by the Hubble Space Telescope and its new camera bears a striking resemblance to the Andromeda system but perhaps at an earlier stage in the interaction process. This further indicates that accretions of small satellites are an important process in building galaxies. Our Galaxy has almost completely swallowed the so-called Sagittarius dwarf galaxy.
Forbes and Beasley intend to follow up this interesting system with further observations to confirm its distance, and Dr Bekki will pursue additional computer simulations.
To download images and two computer simulations of galaxy shredding by Bekki see: http://astronomy.swin.edu.au/
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Contact: Heather Crosling, Media Liaison on 03 9214 5968 or 0416 174 962
Associate Professor Duncan A. Forbes+61 3 9214 4392
