The 2020/21 period has proven to be another great one for discoveries and improvements for the Murchison Widefield Array (MWA). Finding a ‘jellyfish’ in space and its first ever pulsar – plus the development of a much-needed new correlator – have all contributed to another bumper year for this hard-working telescope, tucked away in one of the most radio-quiet parts of the world.
An interferometric radio telescope in outback Western Australia, the MWA is a fully operational precursor instrument to the future low-frequency Square Kilometre Array (SKA). 4,096 dipole antennas arranged in 256 regular grids (called ‘tiles’) make up the front-end of the telescope, spread over several kilometres within the Murchison Radio-astronomy Observatory (MRO). Data from the antennas is processed onsite via a correlator, before being transmitted to the Pawsey Supercomputing Centre for long-term storage. While the front-end works hard observing and processing data, the back-end of the telescope translates to an online platform, the MWA node of the All-Sky Virtual Observatory (MWA-ASVO). Through this platform, scientists are able to access calibrated MWA data – allowing them to make their spectacular discoveries.
Published in The Astrophysical Journal in March 2021, the detection of a radio phenomenon in the cluster of galaxies known as Abell 2877 was made using the MWA by PhD candidate Torrance Hodgson. This ultra-steep spectrum source – dubbed the ‘USS Jellyfish’ – was observed to resemble the well-known shape of the sea creature with dangling tentacles, but only at very low radio frequencies. In that sense, the USS Jellyfish is a record breaker as it is the ‘steepest’ synchrotron source measured to date. This means the ghostly emission cannot be observed at higher frequencies. While bright at regular FM radio frequencies, it vanished almost completely at 200 MHz, stunning the radio astronomy community with its rapid disappearing act.
The discoverers have theorised that the emission was created by plasma, scattered by supermassive black holes billions of years ago and recently reignited by shock waves passing through the galaxy cluster. The USS Jellyfish, stretching to over a third of the Moon’s diameter when observed from Earth, is believed to be just one of many ultra-steep spectrum sources – the rest thought to be lurking just outside the observable reach of radio astronomers until the future SKA comes online. SKA-Low will have far greater resolution and sensitivity than the MWA, and with construction set to commence within the next year, it might not be too long before radio astronomers see more space jellyfish swim into existence during their observations.
Some vital improvements are currently underway at the MWA, revolving around the launch of ‘MWAX’ – a new correlator designed with increased functionality to remove arbitrary limits and support more flexible observing modes and the expansion of the telescope.
Commissioning of MWAX commenced in mid-2021 and when complete, MWAX will represent a signiﬁcant technological and scientific achievement for the MWA. In-house software development, procuring and benchmarking state-of-the-art hardware systems, end-to-end testing, deployment, installation on site, and the technical and science commissioning will form the crux of this highly anticipated upgrade. It is expected that MWAX will enable a broader range of science cases and increase the quality and availability overall of MWA data.
MWAX is funded via a NCRIS Contingency Reserve grant provided to Curtin University and administered by AAL.
In April 2021, the detection of a previously unknown pulsar was announced via the publication of a paper in The Astrophysical Journal Letters. The low-luminosity pulsar was found using the MWA – a first for the radio telescope.
Pulsars are created by supernova explosions when massive stars reach the end of their lives. One result of such an explosion can be a collapsed core known as a pulsar – a small, incredible dense object with a strong magnetic field and a rapid spin. As it spins, a pulsar sends electromagnetic radiation out into space from its magnetic poles, which can be picked up at radio wavelengths by telescopes such as the MWA.
The discovery was made by PhD Student Nick Swainston at the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR), while processing data from an ongoing MWA survey. Processing of this type can be incredibly challenging, especially at the frequency bands of the MWA, but fortunately researchers involved in this discovery were awarded time on the OzSTAR supercomputer. Operated by Swinburne University of Technology and supported by AAL via NCRIS, OzSTAR allowed them to crunch the enormous amounts of data made available through the MWA pulsar survey. Time on OzSTAR was allocated to the team at ICRAR by the Astronomy Supercomputing Time Allocation Committee (ASTAC). ASTAC is managed and operated by AAL and funded via the NCRIS program, and ICRAR-Curtin astronomer Dr Ramesh Bhat says they could not have made the finding without it.
“ASTAC time has been very important for us. Given the small size of our team and the limited resources at hand, we wouldn’t have managed to get here without the consistent support we received via the ASTAC allocation.”
There is also an expectation that this finding may be merely the beginning, and that many more pulsars will be discovered by analysing the remaining MWA survey data using a supercomputer like OzSTAR – currently, only around one percent of this has been processed. New MWA Director Professor Steven Tingay believes there is likely a large population of pulsars awaiting discovery in the Southern Hemisphere, and that the MWA and future SKA are well placed to find them.
“This finding is really exciting because the data processing is incredibly challenging, and the results show the potential for us to discover many more pulsars with the MWA and the low-frequency part of the SKA.”
These characteristics make the array invaluable for quickly mapping the sky and studying rare and faint events as they happen.
In addition to contributions from partner institutions, funding for MWA is provided by NCRIS via AAL. This funding provides support for staff salaries, infrastructure maintenance, utilities, and MRO site costs. AAL’s contribution of operations funding to the MWA ensures support is provided to the globally distributed network of researchers, engineers, planners, and managers dedicated, on behalf of the astronomical community, to the realisation of the SKA.
AAL would like to thank MWA Project Officer Mia Walker for her contribution of information for this story, and for co-authoring several sections.