From AAAS: “New radio telescope in South Africa will study galaxy formation”

AAAS

From AAAS

Jun. 19, 2018
Daniel Clery

SKA Meerkat telescope, 90 km outside the small Northern Cape town of Carnarvon, SA

Today, the Square Kilometre Array (SKA), a continent-spanning radio astronomy project, announced that Spain has come on board as the collaboration’s 11th member. That boost will help the sometimes-troubled project as, over the next year or so, it forms an international treaty organization and negotiates funding to start construction. Meanwhile, on the wide-open plains of the Karoo, a semiarid desert northeast of Cape Town, South Africa, part of the telescope is already in place in the shape of the newly completed MeerKAT, the largest and most powerful radio telescope in the Southern Hemisphere.

The last of 64 13.5-meter dishes was installed late last year, and next month South African President Cyril Ramaphosa will officially open the facility. Spread across 8 kilometers, the dishes have a collecting area similar to that of the great workhorse of astrophysics, the Karl G. Jansky Very Large Array (VLA) near Socorro, New Mexico.

NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

But with new hardware designs and a powerful supercomputer to process data, the newcomer could have an edge on its 40-year-old northern cousin.

“For certain studies, it will be the best” in the world, says Fernando Camilo, chief scientist of the South African Radio Astronomy Observatory in Cape Town, which operates MeerKAT. Sensitive across a wide swath of the radio spectrum, MeerKAT can study how hydrogen gas moves into galaxies to fuel star formation. With little experience, South Africa has “a major fantastic achievement,” says Heino Falcke of Radboud University in Nijmegen, the Netherlands.

MeerKAT, which stands for Karoo Array Telescope along with the Afrikaans word for “more,” is one of several precursor instruments for the SKA. . The first phase of the SKA could begin in 2020 at a cost of €798 million. It would add another 133 dishes to MeerKAT, extending it across 150 kilometers, and place 130,000 smaller radio antennas across Australia—but only if member governments agree to fully fund the work. Months of delicate negotiations lie ahead. “In every country, people are having that discussion on what funding is available,” Falcke says.

With MeerKAT’s 64 dishes now in place, engineers are learning how to process the data they gather. In a technique called interferometry, computers correlate the signals from pairs of dishes to build a much sharper image than a single dish could produce. For early science campaigns last year, 16 dishes were correlated. In March, the new supercomputer came online, and the team hopes to be fully operational by early next year. “It’s going to be a challenge,” Camilo says.

MeerKAT’s dishes are smaller than the VLA’s, but having more of them puts it in “a sweet spot of sensitivity and resolution,” Camilo says. Its dishes are split into a densely packed core, which boosts sensitivity, and widely dispersed arms, which increase resolution. The VLA can opt for sensitivity or resolution, but not both at once—and only after the slow process of moving its 27 dishes into a different configuration.

The combination makes MeerKAT ideal for mapping hydrogen, the fuel of star and galaxy formation. Because of a spontaneous transition in the atoms of neutral hydrogen, the gas constantly emits microwaves with a wavelength of 21 centimeters. Stretched to radio frequencies by the expansion of the universe, these photons land in the telescope’s main frequency band. It should have the sensitivity to map the faint signal to greater distances than before, and the resolution to see the gas moving in and around galaxies.

MeerKAT will also watch for pulsars, dense and rapidly spinning stellar remnants. Their metronomic radio wave pulses serve as precise clocks that help astronomers study gravity in extreme conditions. “By finding new and exotic pulsars, MeerKAT can provide tests of physics,” says Philip Best of the University of Edinburgh. Falcke wants to get a better look at a highly magnetized pulsar discovered in 2013. He hopes it will shed light on the gravitational effects of the leviathan it orbits: the supermassive black hole at the center of the Milky Way.

Other SKA precursors are taking shape. The Australian SKA Pathfinder (ASKAP) at the Murchison Radio-astronomy Observatory in Western Australia is testing a novel survey technology with its 36 12-meter dishes that could be used in a future phase of the SKA.

SKA/ASKAP radio telescope at the Murchison Radio-astronomy Observatory (MRO) in Mid West region of Western Australia

Whereas a conventional radio dish has a single-element detector—the equivalent of a single pixel—the ASKAP’s detectors have 188 elements, which should help it quickly map galaxies across large areas of the sky.

Nearby is the Murchison Widefield Array (MWA), an array of 2048 antennas, each about a meter across, that look like metallic spiders.

SKA Murchison Widefield Array, Boolardy station in outback Western Australia, at the Murchison Radio-astronomy Observatory (MRO)

Sensitive to lower frequencies than MeerKAT, the MWA can pick up the neutral hydrogen signal from as far back as 500 million years after the big bang, when the first stars and galaxies were lighting up the universe. Astronomers have been chasing the faint signal for years, and earlier this year, one group reported a tentative detection. “We’re really curious to see if it can be replicated,” says MWA Director Melanie Johnston-Hollitt of Curtin University in Perth, Australia.

If the MWA doesn’t deliver a verdict, the SKA, with 130,000 similar antennas, almost certainly will. Although the MWA may detect the universe lighting up, the SKA intends to map out where it happened.

The American Association for the Advancement of Science is an international non-profit organization dedicated to advancing science for the benefit of all people.

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