An Australian-developed algorithm has allowed researchers at the CSIRO to map, for the first time, Centaurus A, an enormous galaxy which emits a radio glow covering an area 200 times bigger than the full Moon.
Developed by the Australian Square Kilometre Array Pathfinder (ASKAP) telescope team, the algorithm allows researchers to resolve imaging issues caused by a massive differential between the “brightness” of the radio waves emitted at the core and edge of the Centaurus A galaxy, based some 14 million light-years away.
“In the centre of the galaxy is a supermassive black hole, 50 million times the mass of our sun, which is incredibly bright,” explains Ilana Feain, of CSIRO’s Australia Telescope National Facility (ATNF).
"Because the centre is so bright we have a dynamic range issue, which means that when using conventional image processing tools the image is saturated in the bright regions and we are unable to detect the faint emission regions around these very bright areas. To resolve this, we needed very sophisticated software processing algorithms and these are something that have only recently been developed.”
Compiling 406 images taken over 1200 hours by the Compact Array radio-telescope based in Narrabrai, NSW, the research team was able to “mosaic” the images together over the course of 10,000 hours of processing time on an Opteron-based Sun cluster.
With the completed image, supplemented by data from the 64-metre radio telescope dish located in Parkes, NSW, the research team can now begin to understand how the most massive galaxies have formed and evolved with time, Feain says.
“The energy released from supermassive black holes at the centre of massive galaxies like Centaurus A is intimately related to the formation of galaxies,” she says.
“But the actual physics of how the energy from a black hole is coupled to the forming galaxy is not well understood. On one hand we see evidence of energy from supermassive black holes being capable of heating and blowing out the gas and dust from a forming galaxy, effectively halting it from forming more stars. On the other hand, as is the case in Centaurus A, we can see that the energy from the black hole has caused gas and dust clouds in the galaxy to heat and collapse and form more stars. We don’t know which scenario is more important on a global scale of massive galaxy formation.”
According to Tim Cornwell, project lead and computing engineer for ASKAP, cracking the imaging challenges of Centaurus A has proved to be a useful test case for future challenges the CSIRO expects to face with the ASKAP telescope.
Due for completion in 2012, ASKAP will act as a path-finding instrument and showcase for Australia’s claim to host the Square Kilometre Array -- a new generation radio telescope with a discovery potential 10,000 times greater than the best present-day instruments.
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