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Array of Hope: Australia and South Africa Vie for Massive Radio Telescope Project

The ambitious, unprecedentedly vast Square Kilometer Array project should open up new realms in astrophysics. But will it live up to its name?
ASKAP telescope at Murchison Radio Observatory



John Matson/Scientific American

MURCHISON SHIRE, Western Australia—The pilot of the eight-passenger Cessna turboprop lines up the nose of his plane with a red-dirt landing strip ahead, a band of cleared Earth not all that different from the flat, sparsely vegetated terrain below.

He eases the plane down to an altitude of 90 meters, then levels off, buzzing the airstrip for a visual inspection. At the remote Boolardy pastoral station here in Western Australia, about 600 kilometers north of Perth, any manner of debris might have blown onto the landing strip since it was last used. Or perhaps a stray cow or goat has wandered into harm's way. But no—the airstrip is clear. The pilot circles back for a gentle landing and taxis the Cessna to a halt near a collection of farm equipment belonging to a nearby homestead. Heat mirages shimmer on the smooth red dirt of the airstrip as a dust devil looms over the airplane's right wing.

This is hard country, a place where the barren wilderness stretches to the horizon in every direction, where termite mounds and the droppings of feral goats are about the only signs of life. But the Boolardy homestead in Murchison is plenty lively, occupied by a rotating cast of engineers, construction workers, scientists and, now, four North American reporters on a government-sponsored visit. Federal and state agencies plunked down about $5 million to purchase some 3,500 square kilometers of this rangeland in 2009, then signed a land-use agreement with the indigenous Wajarri Yamatji people worth more than $18 million to allow for construction on a core region of almost 130 square kilometers. Since that time the site has seen numerous upgrades in power generation, water storage and high-speed communication infrastructure. The dirt roads leading from the homestead to the core of the site have been graded to a flatness and smoothness that rivals most highways.

Nine thousand kilometers to the west, across the Indian Ocean, a similar scene is unfolding. Near the town of Carnarvon in the Karoo region of South Africa, a government-backed project has acquired 140 square kilometers of farmland about 450 kilometers northeast of Cape Town. Surrounding the remote plot is a newly designated 125,000-square-kilometer protected reserve. Like Murchison, the Karoo site has undergone a progressive makeover since its 2008 purchase—better roads, new fiber-optic cables, new power lines—to become ever more incongruous with its rugged surroundings.

The multibillion-dollar reason for all this parallel activity in Australia and South Africa has recently become clearer. At each of the far-flung sites, a handful of radio telescopes has sprung up like clusters of white mushrooms blooming from the red earth. Radio telescopes, which look like oversize satellite dishes, receive emissions from space at the longest wavelengths on the electromagnetic spectrum. Those emissions may come from natural radio sources in the galaxy, such as the spinning stellar remnants known as pulsars, or may originate as shorter-wavelength signals, such was microwaves, that have been stretched into the radio band as they travel from distant sources, across an expanding universe, to reach Earth.

Australia has six dishes, with designs on 30 more; South Africa has built seven of a planned 64. When the two projects, the Australian Square Kilometer Array Pathfinder (ASKAP) and the Karoo Array Telescope (MeerKAT), are finished, each will be among the most powerful radio observatories in the world. But both countries have set their sights on a bigger prize. South Africa is building MeerKAT, and Australia is building ASKAP, in the hopes of landing the $2-billion Square Kilometer Array, one of the most ambitious telescope projects in history.

In 2012 an international consortium will choose Murchison or Karoo as the home of the Square Kilometer Array, or SKA, a vast network of 15-meter radio telescopes that, as proposed, would comprise 3,000 steerable dishes that pivot on multiple axes to aim at celestial targets. (The project's name is a bit of a misnomer; the dishes would together provide about a half a square kilometer of collecting area.) With an array of interconnected dishes, astronomers can yoke all the telescopes together, essentially combining the collective observing power of the group into one super telescope. Adding more collecting area—that is, building more dishes—boosts the array's sensitivity, whereas spacing the dishes out across great distances gives the array better resolution.

A complementary array of stationary antennas—more like old-fashioned rooftop TV antennas than satellite dishes—would collect lower-wavelength radio waves and would bring the project closer to its nominal square kilometer of coverage. At full build-out, slated for the mid-2020s, the digital output from the SKA could exceed the current volume of Internet traffic worldwide. The project's cost would be split among a number of partner countries. But just how many of those 3,000 planned dishes will ever be built, and just who will foot the bill for them, remain unsettled.

Regardless, both South Africa and Australia are eager to reap the economic benefits and scientific glory that would come from hosting such a world-beating project. And representatives of each nation are quick to point out the advantages of their respective site.

"I think Australia is the site for the SKA, undoubtedly," says Phil Diamond, the chief of astronomy and space science for the Commonwealth Scientific and Industrial Research Organization (CSIRO), the Australian national science agency that is leading the country's bid for the project. Diamond points to the extreme remoteness of the Murchison site and the sparsely populated region surrounding it, which means a quieter background of radio waves generated by Earthlings—key for sensitive radio astronomy. "There are no people, no mobile phones, no microwave ovens, no garage-door openers," Diamond says. His CSIRO colleague Brian Boyle, director of the Australian SKA project, is fond of tossing off population density figures for Murchison Shire—in "nanopeople" per square meter. "It has no towns," Boyle says of the shire. "It prides itself on having no towns."

The South African contingent contends that remoteness is not everything and that the Karoo site offers important cost savings. "It's a lot cheaper to build infrastructure in South Africa, and it's a lot cheaper to carry out maintenance and upkeep in South Africa," says Bernie Fanaroff, project director for that country's SKA program. Plus, the MeerKAT site now has grid power, which the ASKAP site does not. Powering thousands of telescopes, their receivers and all the associated computer equipment would be costly off the grid. Justin Jonas, the South African SKA associate director for science and engineering, sums up his nation's rationale for choosing a proposed home for the SKA as, "Let's find a site that is remote enough to satisfy the science goals, but is not so remote that it's going to cost an arm and a leg to establish anything there."

Diamond says that the core of the SKA, where about half of the telescopes would be clustered, would require about 40 megawatts of electricity. The other half of the telescopes would fan out in long arms that would stretch to New Zealand to maximize the array's resolution; in Africa the arms would spread across several nations.

Although Murchison shire is an ideal site for solar power—it has both abundant land and abundant sunshine—a 40-megawatt solar plant would be a huge undertaking on its own. "Energy is a big problem for us," Diamond acknowledges.

An international committee short-listed the two sites in 2006 from four proposals, which also included a pitch from China and one from Argentina and Brazil. "The SKA science board said that these two sites were acceptable" from a science standpoint, says Cornell University astronomer Yervant Terzian, a member of the SKA siting group. "I think that's pretty good. The rest is refining."

Both Murchison and Karoo are radio-quiet enough to have satisfied the baseline science requirements for the SKA, but some interference is unavoidable. GPS satellites, commercial aircraft and omnipresent human transmissions all contribute radio pollution to the airwaves. Measurements of the sites' levels of radio interference and atmospheric disturbances are ongoing, but any number of other factors will come into play. Which site has the best infrastructure? Which political climate is more inviting? Where will the project deliver the most cultural benefits? "It's a whole long list of criteria," says Cornell's James Cordes, chair of the U.S. SKA consortium, a group of U.S. institutions that have been working to develop the SKA.

Australia has the advantage of a long legacy of leadership in radio astronomy. After World War II, when radio astronomy began in earnest, one of the leading teams in the field was a CSIRO group led by John G. Bolton and J. L. Pawsey. The 2000 film The Dish, about the Parkes radio telescope, is a major cultural touchstone. But South Africa has been steadily investing in radio astronomy, and Jonas says that the nation is no longer an underdog facing doubts about technical expertise. "I think we're well beyond that now," he says.

Roy Booth, an astronomer at the Hartebeesthoek Radio Astronomy Observatory in South Africa who serves as associate director for science operations on MeerKAT, says that bringing a world-class science project to Africa would have great cultural benefits. "The stars, of course, are something you see whether you’re rich or poor," Booth says. "If we could set up the SKA as sort of a World Cup for science, we might interest the people in the villages."

Pulsar populations and the deep universe
Cordes's interest in the SKA stems partly from the array's capacity for finding pulsars, highly magnetized stellar remnants that spin extremely rapidly. Some can complete hundreds of revolutions in a single second. Pulsars emit a beam of radiation; as a pulsar rotates its beam sweeps across Earth, like a lighthouse panning its light beam across a ship. But no lighthouse can compete with a pulsar's reliability: The beams of some pulsars sweep through space with a regularity on par with the ticking of an atomic clock.

Pulsars—dense, massive objects with the capacity to serve as a precision clock—are ideal natural laboratories for testing the predictions of general relativity, Albert Einstein's theory of gravitation. Russell Hulse and Joseph Taylor earned the 1993 Nobel Prize in Physics for their discovery of a pulsar orbiting another massive object in 1974, when both were at the University of Massachusetts Amherst. Their so-called binary pulsar allowed for the indirect confirmation of the existence of gravitational waves, ripples in the fabric of space and time that emanate from the movement of massive bodies. Hulse and Taylor found their binary pulsar, PSR 1913+16, using the 305-meter Arecibo observatory in Puerto Rico, currently the largest radio dish in existence.

But Arecibo is a fairly noisy site, as far as radio interference is concerned, and a full SKA would have much more collecting area—and hence more sensitivity to faint sources of radio waves. "With the SKA, we want to do a full galactic census of pulsars," Cordes says, "and that means try to detect every damn one of them in the galaxy." Astronomers have already located about 2,000 pulsars, but there could easily be 10 times that many in just the Milky Way. Although 2,000 pulsars makes for a sizable sample, the most interesting pulsars—those in binary pairings such as PSR 1913+16 and the rapid spinners known as millisecond pulsars—are relatively rare. A full census of pulsars might even reveal a few oddballs that could reveal gaps in our understanding of gravity. "We would love to find a pulsar orbiting around a black hole," CSIRO's Diamond says. "That is probably the regime in which general relativity will begin to break down."

With a powerful enough telescope, irregularities in the measured arrival time of pulses from millisecond pulsars could also mark the presence of gravitational waves passing through the local universe. Those gravitational waves compress and stretch space, and the radio waves passing through it, throwing off the pulsar's usually predictable ticking. "These waves should be all over the place," Cordes says. "They affect every line of sight that you look at."

By collecting long-wavelength radio waves, the SKA might also be able to see deep into the early universe, when the first galaxies and stars appeared. (Because of light's finite speed, astronomers can see the universe as it existed long ago by looking at ancient, distant objects in the sky whose light was emitted billions of years ago but is only now reaching Earth.) Neutral hydrogen, which dominated the first few hundred million years following the big bang, emits photons at a telltale wavelength in the microwave band; those microwave photons are stretched to longer radio wavelengths in their journey across a vast, expanding universe. SKA could chart the early universe's neutral hydrogen to peer into the cosmic dark ages, the time before luminous stars and galaxies emerged and ionized the intergalactic hydrogen.

That would give astronomers a glimpse at a mostly inaccessible stage of structure formation early in the universe's evolution. "I would like to see radio images of the first galaxies being born after the big bang," Terzian says. "I can tell you, this would be thrilling."

Surpassing Arecibo
Just how large the telescope array will become—and just how revolutionary its science—depends on financing. En route to the Murchison site, Boyle, a tireless pitchman for his project, smiles at the mention of the full-scale, 3,000-dish SKA. He acknowledges that the project could stall at partial build-out, that it may take awhile to move beyond a few hundred telescopes.

But even a stunted SKA would still be the largest instrument of its kind. It could easily dwarf the Very Large Array in New Mexico, one of the premier radio telescope arrays on Earth, which features 27 dishes, each 25 meters across. And it would have more collecting area than Arecibo, the biggest single dish on the planet. "It would pass Arecibo at considerably less than full build-out," Cordes notes. With only about 400 dishes, each 15 meters in diameter, the SKA would boast more collecting area than Arecibo with considerably less radio interference.

On April 2, the vision of the radio telescopes now dotting the Australian and South African landscapes someday giving way to a mammoth cluster of 3,000 dishes began to look a little untenable. A coalition of nine countries' national science agencies formally signed on to the Square Kilometer Array, establishing a founding board and a project office at Jodrell Bank Observatory in England. But the list of signatories did not include the U.S. National Science Foundation (NSF), which had been expected to contribute one third of the funds for the project. Another third would have come from Europe—and indeed France, Germany, Italy, the Netherlands and the U.K. did sign on—with the final third coming from the rest of the international partners.

"NSF did not sign on to the founding board agreement because this included a pledge to participate in the next phase at a significantly enhanced funding level," James Ulvestad, the NSF division director for astronomical sciences, said in an e-mail. A 2010 report from the National Research Council, intended to guide U.S. astronomy priorities in the coming decade, had concluded that participating in the SKA was not possible in the current fiscal environment unless the country shut down other "highly productive facilities"; Ulvestad said that the NSF had accepted that conclusion. He noted that the U.S. has already made investments in the SKA, such as supporting technology development for the project, and "will continue to make such investments as funds permit, if independent reviews give them very high priority."

Before that decision was announced, Cordes had stressed that the SKA would be a modular instrument—it would work great with 3,000 dishes, sure, but even one dish can do science. "I think we need to break through some of these perceptions," he said, that the SKA is "this big behemoth with a price tag in the billions."

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