In preparation for the Square Kilometer Array (SKA) radio telescope project set to start construction in 2018, the CSIRO’s recently unveiled Australia SKA Pathfinder (ASKAP) radio telescope array has been used to demonstrate and prove the technology involved. With the images it has captured so far, it has also shown its ability to operate as a fully-fledged radio telescope in its own right.
Located at the Murchison Radio-astronomy Observatory in Western Australia, ASKAP has taken early images with just six of the 36 antennas in its array so far commissioned. Yet, even with so few instruments on line, these images show a degree of unexpectedly high resolution. Dr David McConnell, who leads the ASKAP Commissioning and Early Science (ACES) team, said that when the team saw the new image, they “practically fell off their chairs."
A radio wave image of a region of sky near the south celestial pole, the ASKAP image covers 10 square degrees of the sky – an area 50 times larger than that of a full Moon – made up of nine intersecting regions captured simultaneously. This was made possible through CSIRO’s use of a special axis of rotation control on each antenna, which kept the array on a fixed orientation to the sky, while its new "phased array feed" (PAF) technology provided the antenna with a wide field-of-view by creating 30 separate simultaneous beams at the antenna feed. The result is an image with a dynamic range of 50,000:1, which is good for a large instrument, but exceptional for so small an array.
"These ASKAP results are generating great excitement in the office of the SKA Organization in Manchester, UK, and at an SKA science meeting currently taking place in Italy, because they clearly demonstrate the revolutionary potential of CSIRO's new phased array feed technology," said Chief of CSIRO Astronomy and Space Science Dr Lewis Ball.
As part of the early testing process, ASKAP also focused on a single galaxy, NGC 253, to produce a color image from radio waves of around 21 cm (8.3 in) in length emitted by neutral atomic hydrogen (HI) gas. The image captured illustrates how much HI is present gauged by the intensity of these waves, as well as the way in which the galaxy is rotating by showing which sections are approaching us, and which are receding.
"What we're looking for here is the equivalent of 'color balance' – if there's a proper balance of the radio waves at all the different frequencies used in the image,” said Dr McConnell. "Happily, that balance is good. The image compares very well with one made by our established Compact Array telescope."
The phased array feeds used for these early tests are of a first-generation design, with procurement under way for improved second-generation PAFs to meet the CSIRO's performance targets. The original PAF design last year won awards for innovation from Engineers Australia.
Currently in development in Australia and South Africa, the Square Kilometer Array (SKA) radio telescope will be 50 times more sensitive than any other radio telescope in existence. It will function over a widespread range of frequencies and will require very high-performance computers and large-capacity links to fully capture and store the enormous amounts of data that it will collect. Phase one of the project will take place from 2018 to 2020, with the goal to deliver a functioning array capable of carrying out the initial science. Phase two will then move towards completion in 2025 for the ultimate SKA system to provide complete sensitivity for frequencies up to at least 14 GHz.
The video below shows the antennas of the ASKAP array in a time-lapse sequence.