South Africa’s MeerKAT radio telescope observes a rare burst of activity from an exotic star, demonstrating outstanding capabilities as a new instrument for scientific exploration
An article published today in The Astrophysical Journal presents the study of a magnetar – a star that is one of the most magnetic objects known in the universe – that awoke in 2017 from a 3-year slumber. Radio observations that could only be made with MeerKAT, a telescope being built in the Northern Cape province of South Africa, triggered observations with NASA X-ray telescopes orbiting the Earth. This first publication in the scientific literature of astronomical discoveries requiring the use of MeerKAT heralds its arrival into the stable of world-class research instruments.
Dr Fernando Camilo, Chief Scientist at the South African Radio Astronomy Observatory (SARAO, which includes the Square Kilometre Array South Africa project), describes the setting one year ago: “On 26 April 2017, while monitoring the long-dormant magnetar with the CSIRO Parkes Radio Telescope in Australia, one of our colleagues noticed that it was emitting bright radio pulses every 4 seconds”. A few days later Parkes underwent a planned month-long maintenance shutdown. Although MeerKAT was still under construction, with no more than 16 of its eventual 64 radio dishes available, the commissioning team started regular monitoring of the star 30,000 light years from Earth. According to Camilo, “the MeerKAT observations proved critical to make sense of the few X-ray photons we captured with NASA’s orbiting telescopes – for the first time X-ray pulses have been detected from this star, every 4 seconds. Put together, the observations reported today help us to develop a better picture of the behaviour of matter in unbelievably extreme physical conditions, completely unlike any that can be experienced on Earth”.
The article, entitled Revival of the magnetar PSR J1622−4950: observations with MeerKAT, Parkes, XMM-Newton, Swift, Chandra, and NuSTAR, has 208 authors. A handful of these are astronomers specialising in the study of magnetars and related stars. The vast majority belong to the so-called MeerKAT Builders List: hundreds of engineers and scientists overwhelmingly from the SKA South Africa project and commercial enterprises in South Africa that over more than a decade have been developing and building MeerKAT – a project of the South African Department of Science and Technology, in which 75% of the overall construction budget has been spent in South Africa.
“MeerKAT is an enormously complex machine”, says Thomas Abbott, MeerKAT Programme Manager. In order to make the exquisitely sensitive images of the radio sky that will allow scientists to better understand how galaxies like the Milky Way have formed and evolved over the history of the universe, the 64 MeerKAT antennas generate data at enormous rates. The challenges involved in dealing with so much data require clever solutions to a variety of problems at the cutting edge of technology. According to Abbott, “we have a team of the brightest engineers and scientists in South Africa and the world working on the project, because the problems that we need to solve are extremely challenging, and attract the best”.
Some of these people were in high school when the project started. “We have implemented a human capital development programme focused on producing the South African engineers and scientists with the skills required to design, build, and use the telescope”, relates Kim de Boer, Head of the SARAO Human Capital Development Programme. Many of these young people are now employed at SARAO, at South African universities, and in the broader knowledge economy.
“The first scientific publication based on MeerKAT data is a wonderful milestone”, says Prof Roy Maartens, SKA SA Research Chair at the University of the Western Cape. “Although MeerKAT isn’t yet complete, it’s now clearly a functioning telescope. We’ve been training a new generation of researchers, and soon our young scientists will be using what promises to be a remarkable discovery machine”.
Early in 2018, SARAO received the first Early Science MeerKAT observing proposals from South African researchers. Later in the year, already approved Large Survey Projects that will use two-thirds of the available observing time over 5 years will start their investigations with the full array of MeerKAT antennas. These 64 dishes, each 13.5 metres in diameter, are distributed across a span of 8 kilometres in a remote area of the Northern Cape. The 64 MeerKAT antennas are standing tall in the Karoo. The official unveiling of the telescope is being planned for the second half of 2018.
“Well done to my colleagues in South Africa for this outstanding achievement”, declares Prof Phil Diamond, Director-General of the SKA Organisation leading the development of the Square Kilometre Array. “Building such telescopes is extremely difficult,” adds Diamond, “and this publication shows that MeerKAT is becoming ready for business. As one of the SKA precursor telescopes, this bodes well for the SKA. MeerKAT will eventually be integrated into Phase 1 of SKA-mid telescope bringing the total dishes at our disposal to 197, creating the most powerful radio telescope on the planet”.
“It’s been a long road getting to this point”, notes Dr Rob Adam, SARAO Managing Director. “It’s required the hard work and support of countless South Africans over more than a decade”. “We’re nearly there with MeerKAT”, continues Adam. “As this first article indicates, the telescope is now beginning to make scientific discoveries. As MeerKAT’s capabilities continue to grow, many more will follow”. “It’s tremendously gratifying to lead a team of such talented and passionate colleagues, who’ve been building in the Karoo a research instrument with few parallels anywhere”, concludes Adam.
About neutron stars, pulsars, and magnetars
Neutron stars are the collapsed remnants of giant stars that in their prime contained approximately 10 times the mass of our Sun. When they run out of fuel, after converting their hydrogen into heavier elements through a chain of nuclear fusion reactions, the outer layers of such stars are ejected in one of the most violent events in the universe, a supernova explosion. A dense core is left, made up mostly of neutrons. Such neutron stars are immensely dense – the size of a city but more massive than the Sun. They also spin rapidly, from once every few seconds up to several hundred times per second and have magnetic fields one trillion times stronger than the Earth’s. As they spin, beams of radio waves, and sometimes X-rays, focused along their magnetic fields, stream out of the neutron star into space. Given a fortuitous alignment, on Earth with the appropriate telescopes one can detect bursts of electromagnetic waves with every turn of the star, in lighthouse-like fashion. These neutron stars are therefore sometimes also known as pulsars, as they appear to pulsate, although in fact they are rotating. About 3000 pulsars are known in our Milky Way galaxy, a few percent of the total population thought to exist. By comparison, our galaxy contains more than 100 billion ordinary stars.
Magnetars are a very rare subset of neutron stars/pulsars. Only two dozen are known in our galaxy. Their magnetic fields are up to 1000 times stronger than those of ordinary pulsars. The energy associated with such fields is so large that it almost breaks the star apart, and they tend to be unstable, displaying great variability in their physical properties and electromagnetic emission. All magnetars are known to emit X-rays, but only four are known to sometimes also emit radio waves. One of these is the subject of the first scientific publication based on MeerKAT data.
New radio telescope in South Africa will study galaxy formation
SOUTH AFRICAN RADIO ASTRONOMY OBSERVATORY
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. 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. 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. 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.