Focusing in on Our Galaxy
An international plan for the largest-ever radio telescope took a step forward last week with the selection of two possible sites and plans for building prototype systems on each of them.
Slated for completion in 2020, the Square Kilometer Array (SKA) will ultimately be built in either Western Australia (with extensions to New Zealand) or South Africa (with extensions into six neighboring countries). The final site will have an actual collecting area of about one square kilometer, divided up among thousands of dishes, spread out over 3,000 kilometers.
This scale will make it 50 times more sensitive than the Very Large Array (VLA) in New Mexico, even after that telescope’s current transformation into the Expanded VLA.
With all that sensitivity, the SKA could bring new power to the search for extraterrestrial intelligence (SETI). The telescope is expected to be so sensitive to the effects of advanced civilizations that it could pick up the equivalent of our airport radar systems coming from anywhere among the nearest million stars in our galaxy.
The SKA will also be able to make a detailed study of the distribution of “dark energy” in the universe, by mapping the distances of a billion galaxies. (One of the most intriguing astronomical findings of recent years, dark energy is found throughout space. It seems to be causing the expansion of the universe to speed up and it accounts for a majority of the universe’s “missing” mass.)
The SKA may even be able to indirectly detect gravity waves–which have never been observed but are widely believed to exist–by detecting tiny changes in the precise rate of radio flashes from hundreds of pulsars.
New technology planned for the SKA’s central section gives it a sort of radio-frequency “fish-eye lens” that can perform massive, all-sky surveys 10,000 times faster than the Expanded VLA, the largest radio array until the SKA comes online.
The finished SKA telescope will have a central array of approximately 2,000 independently mounted dishes (each 10 to 15 meters across), surrounded by some 200 smaller arrays of about 20 dishes each. (The exact sizes and design of the arrays are still being decided on.)
The concept for the new telescope was based on the Allen Telescope Array (ATA) under construction in California, financed by Microsoft cofounder Paul Allen. That array, which will ultimately include more than 350 individual six-meter dishes, was the first to use standardized, mass-produced hardware instead of the custom-built giant dishes in other radio telescopes. With just 30 of the dishes installed, the ATA is already conducting useful research; one of the major advantages of such modular systems is that even a partial array can be quite powerful.
When finished, the Allen array will be only around one percent of the size of the SKA, yet it will be a crucial proving ground for the necessary technologies, says SKA project office director Richard Schilizzi. “We’ll learn a lot from that–everything from the receivers they’ve got, to the feed that channels the radio waves into the receiver,” he says. It’s one of several projects underway that will test the various technologies.
Another groundbreaking technology for the SKA will be a section in the center–sort of a hole in the center of a donut of raised dishes–which will consist of flat panels laid out on the ground. Unlike the dishes, which must each be mechanically oriented toward the area of sky being observed, the “pointing” of the flat array is purely electronic, as in some modern radar systems. Consequently, researchers can study different areas of the sky without physically moving any parts of the array, and can even observe several different regions in the sky at the same time.
“You can have multiple groups using the telescope at once,” Schilizzi says. His team is currently trying to determine just how much of the sky they will be able to see simultaneously.
Headquartered in Dwingeloo, Netherlands, the SKA project is a collaboration of scientists in 17 countries, and is expected to cost around 1 billion euros (US$1.3 billion).
The current plan is to begin scientific operations in 2014 with about 10 percent of the array completed, then continue observations as the array gradually expands.
“As soon as you have two telescopes you can start doing science,” Schilizzi says.
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