The ‘cosmic clocks’ preparing SKAO for early science

Pulsars are rapidly spinning neutron stars with strong magnetic fields. Their rapid and regular rotations make them incredibly precise space clocks, as accurate as the best atomic clocks on Earth.  

The Vela pulsar is one of the brightest pulsars in the Southern sky and, at about 900 light years away, one of the closest to Earth. It's one of a growing catalogue of close to 50 known pulsars so far observed as part of the commissioning phase of SKA-Low, which is under construction on Wajarri Yamaji Country in Western Australia. 

The signal above shows 100 pulses from the Vela pulsar and has been sonified to make it more broadly accessible.

“SKA-Low is a hugely complex scientific instrument – you can't just plug it in and expect everything to work perfectly. By comparing our pulsar observations with existing data, we can make sure the system is working as intended, and fine-tune it where needed," said Dr Shivani Bhandari, SKA-Low Commissioning Scientist. 

SKA-Low's two-metre-tall antennas are grouped into “stations” of 256 antennas each; this observation used four complete stations, comprising 1,024 antennas in total.  

As more and more antennas are added to the telescope, teams are commissioning and calibrating stations individually, and ensuring they work together as one big telescope.  

"These observations are a vital part of the commissioning process because they allow us to test the sensitivity of each station as it comes online,” Dr Bhandari said. 

The work is part of the Observatory’s efforts to get the telescope ready to be used by the scientific community from 2027 – just 18 months from now – while it is still a partial array, and while construction continues.  

In that phase, called science verification, the Observatory will for the first time open its SKA-Low telescope to requests from the science community to help further fine-tune it, ahead of longer and more complex observation campaigns later this decade.  

“The science capability of this very flexible telescope is being tested through the overall Science Commissioning programme. In addition to pulsar observations, we are also using the telescope in its imaging mode to observe radio emission from distant galaxies containing supermassive black holes. The brightest of these objects can be used to understand how we will calibrate the complete system to make the exquisite images that SKA-Low will be capable of generating,” said Dr George Heald, SKA-Low Lead Commissioning Scientist. 

“As the telescope increases in scale, our commissioning tests will also get more complex and lead to the validation of specific observing modes for use in the Science Verification process.” 

More observations are planned over the coming months, as the teams continue installing antennas and testing the rapidly growing telescope.

Construction progresses 

Construction of both SKA telescopes is progressing apace.  

In Australia, more than 6,400 SKA-Low antennas have been installed at Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-astronomy Observatory. This represents close to 5% of SKA-Low's full size; the telescope will ultimately have 131,072 antennas spread across 74 km. 

The SKA-Mid telescope, which will ultimately comprise 197 dishes, is under construction simultaneously in South Africa. It is being built among the antennas of SARAO's existing MeerKAT telescope, a world-class facility in its own right, which will eventually be integrated into SKA-Mid. The construction is being managed around MeerKAT operations in order to minimise disruption to the science already taking place. Dish assembly is taking place alongside major infrastructure work, with more than 50 dish foundations now complete. 

Hardware and software for both telescopes are being manufactured and developed in SKAO partners countries all over the world. 

A dozen countries are involved supplying hardware and software for SKA-Low. The antennas themselves are made in Italy, while the low noise amplifiers that sit on top of them to boost the weak astronomical signals we are observing are made in the United Kingdom. The processing boards which combine the signals from each station are made in Italy, and several other countries contribute other parts. The first few racks to process the data are being installed at the Pawsey Supercomputing Research Centre in Perth. 

Pulsars: precise cosmic clocks 

Pulsars emit a pulse of radio waves like a lighthouse beam, which radio telescopes can detect when the beam points towards Earth. They provide opportunities to test Einstein's theory of General Relativity in the most extreme environments, for example observing a pulsar orbiting a black hole, where the strength of gravity causes space-time to become extremely warped. The SKA telescopes will also time an array of millisecond pulsars (which are both faster and rarer than an average pulsar) to better than 10,000,000th of a second, to detect the tiny delay in signals caused by the ripples of gravitational waves passing through our galaxy. 

The Vela pulsar, located at the heart of a supernova remnant, can be found in the Vela constellation in the southern hemisphere sky. It was formed around 12,000 years ago when a star exploded, creating a supernova that would have been visible in the sky for weeks even during daytime. The star then collapsed upon itself, creating a dense spinning neutron star the size of a small city but the mass of up to two Suns, rotating 11 times per second. 

The SKAO recognises and acknowledges the Indigenous peoples and cultures that have traditionally lived on the lands on which our facilities are located. The data was obtained at Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-astronomy Observatory. The SKAO and CSIRO acknowledge the Wajarri Yamaji as the Traditional Owners and Native Title Holders of the observatory site.