I feel like yesterday’s depressing (but popular!) post painted a bit gloomier picture of the future of astronomy and space science than the reality warrants. Today, I thought I might cheer you up with an inside view of one of the neatest pieces of scientific instrumentation under construction today: a fantastic radio telescope called the Australian Square Kilometer Array (SKA) Pathfinder (ASKAP).
Square Kilometer Array
As the name implies, ASKAP is a testbed for technologies that will be used in a much larger project, the Square Kilometer Array. The SKA warrants a post of its own, and I hope to write one up in the next few days. Suffice is to say, the SKA will stand head and shoulders above any other radio telescope ever built. To be constructed in either the Australian outback, or across South Africa, the SKA will feature nearly 3000 separate dish antennae, with the farthest dishes located more than 3000 km from each other, and whose total area will be at least one square kilometer. It will be able to scan the sky in a huge range of frequencies, from 70MHz to 10GHz. That ratio of the highest frequency to the lowest is roughly 71 times more than the range our eyes can see. The SKA will be able to examine with unprecedented detail the cool gas that fills the structure of most galaxies (including our own!) and, using polarization, probe the magnetic fields throughout the cosmos. It will be a key tool in determining the way in which galaxies evolve, the mysteries still surrounding Quasars and Active Galaxies, and more closely map the structure of our galactic home, the Milky Way.
The SKA will be so sensitive, that one of the current debates among radio astronomers is whether the noise level in the telescope will in fact be limited by confusion. Confusion is a problem similar to Olbers’ paradox, where the sky is so full of dim objects that nearly every beam contains at least one source! (a radio astronomy term similar to pixels in a digital camera, a beam is the smallest resolvable “chunk” of an image)
The SKA will pump out over a petabyte (1 million gigabytes) per second in raw data (that figure is more than 100 times the data rate flowing through the entire internet), and require more than 100 petaflops of computational power to correlate (this is nearly twice the power of the 500 fastest supercomputers in the world combined, and about 40 thousand times faster than the best NVIDIA GPU you can buy right now). Just the infrastructure alone for the SKA will be revolutionary, in the same way that the infrastructure built for the Large Hadron Colider was revolutionary (when Tim Berners Lee invented HTTP and the web, he was working as a CERN contractor preparing technologies for the LHC). It is no stretch to call the SKA the LHC of astronomy.
Naturally, before one engages in a massive undertaking like building the SKA, you begin by working on smaller, proof of concept designs. One of these has already been completed, and sits as happily as a telescope can in the Dutch countryside. The Low Frequency ARray, or LOFAR, is covers the low energy end of the electromagnetic spectrum that the SKA will also be examining. With additional telescopes, LOFAR may actually usurp the SKA’s title, and have a total collecting area of 1 square kilometer!
In addition to LOFAR, both South Africa and Australia are building what are essentially smaller versions of the whole SKA. South Africa’s telescope is called MeerKAT, and Australia has ASKAP. Since I’m not involved with MeerKAT, I will be focusing on ASKAP.
The Pathfinder project I am involve with through the University of Calgary is ASKAP. Even though this telescope is “just” a pathfinder, it will in many ways be the most powerful radio telescope in the world when it is completed.
Located at the Murchison Radio Observatory in western Australia, ASKAP is blanketed in a radio-quiet bubble 150 km in all directions, making it one of the most isolated places on Earth, as only a few dozen people live within this area, deep in the Australian desert. The telescope itself is an array of 36 12 meter dishes, spread out over just under 4 kilometers. The reason for the strange seeming pattern of the dishes is because of a property in interferometry (using multiple antennae as a big telescope) called spatial frequencies. Without including a variety of baselines (distances from the center), the telescope loses sensitivity to structures of certain size.
There are a couple of really neat features in ASKAP that make it quite amazing. The most obvious is the phased-array feeds. Rather than operating in the “single pixel” mode that most radio telescopes are confined to, each ASKAP dish contains a 92 receiver feed system. This gives the telescope a field of view of 30 square degrees, a massive improvement over other telescopes. Since a large chunk of the sky is visible in each frame captured by the telescope, large sky surveys will take much less time to complete, despite being much deeper than past surveys. Phased Arrays are to radio astronomy what CCDs where to optical astronomy, and projects like the SKA would be impossible without them. A more prosaic innovation in ASKAP is the way that it is being manufactured. Rather than being built on site by a specialized contractor, ASKAP’s dishes will be constructed in China, and assembled after shipping them to the MRO. It would be impossible to build the SKA within a reasonable budget without this sort of outsourcing mass production. So far, the dishes that have been assembled have exceeded specification, so things are looking good in this front.
Once ASKAP nears completion, it will begin two of the biggest radio sky surveys ever made: the Evolutionary Map of the Universe (EMU) and the Polarization Sky Survey of the Universe’s Magnetism (POSSUM). These two projects warrant their own blog posts, but let me just briefly say that they will be the largest total intensity and polarized intensity sky surveys ever completed, and that even before the SKA is powered on for the first time, these data from ASKAP will be unveiling the universe in unprecedented detail.
So there you have it. For radio astronomers at least, the future is very bright indeed. I have a feeling this sort of project, with large international cooperations working together to build massive, decadal projects will come to become the norm in astronomy. A lot of the big questions require big tools to answer, and the SKA is a very big tool indeed. Its smaller predecessor will still be a very powerful tool to unlock the keys of the cosmos, and I look forward to getting my hands on the data that ASKAP will produce through EMU and POSSUM. If you have any questions about ASKAP, the SKA, or radio astronomy in general, leave a comment and I will try to answer you as best I can.