South Africa’s MeerKAT radio telescope has observed a rare burst of activity from an exotic star.
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 three-year slumber.
Radio observations that could only be made with MeerKAT, a telescope being built in the Northern Cape, triggered observations with NASA X-ray telescopes orbiting the Earth.
The 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 four 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 mostly from the SKA South Africa project and commercial enterprises 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,” explains 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 Professor 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 fie years will start their investigations with the full array of MeerKAT antennas. These 64 dishes, each 13,5m in diameter, are distributed across a span of 8km in the Northern Cape.
“Well done to my colleagues in South Africa for this outstanding achievement,” says Prof Phil Diamond, director-general of the SKA Organisation.
“Building such telescopes is extremely difficult, 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,” adds Dr Rob Adam, MD of SARAO. “It’s required the hard work and support of countless South Africans over more than a decade.”
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 1-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 3 000 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 1 000 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.