An Iconic Australian Telescope, Upgraded for Future Science

Australia’s deep history in radio astronomy dates back decades, to a time when the second great war had ended and radar technology had emerged as a gateway into studying the heavens. One Australian radio telescope, in particular, has its roots grounded firmly in these early days of pioneering work in radiophysics, with a story punctuated with discovery, triumph and debate. 

It is the story of the Molonglo Observatory. 

Located just outside the city of Canberra, the observatory is not as typical in appearance as other familiar radio telescopes, such as the CSIRO Parkes and ASKAP instruments. There is no parabolic dish antenna that steers in different directions, nor an array of dipole-like structures that resemble the spider-like Murchison Widefield Array telescope. In fact, when people first come across it, they often mistake it for a giant irrigator. As it is big. Really big. Over one and a half kilometres in length. 

If you could get an aerial view of the Molonglo observatory, you might notice it is shaped like a giant plus symbol, or cross featuring a north-south (N-S) and east-west (E-W) arm. In fact, you could spot the large structure, with Google Earth today. 

Officially known as the Molonglo Observatory Synthesis Telescope (MOST), the design sports two, long, intersecting semi-cylindrical arms (12-metres in diameter) that look similar to the half-pipes often used by skateboarders and snowboarders during sporting events. 

Up until recently, the N-S arm was out of action having been decommissioned about 40 years ago and leaving the E-W arm to do all the heavy lifting, but with some excellent gains made in the technology that sits behind radio telescopes, part of the N-S arm is now operational again (and has been for the last 3 years), gathering data under the new name of UTMOST - a joint project between the University of Sydney and Swinburne University of Technology.

The telescope itself takes advantage of the Earth’s rotation, sweeping its beams across the sky and searching a large field of view for transients and other radio sources. Though, parts of it can also tilt and utilise phase delay methods, making it ‘steerable’ and giving it the ability to track sources across the sky for longer periods. Historically it has been used to discover thousands of distant galaxies, supernova remnants and more. But these days, under UTMOST, it is mostly timing pulsars and keeping a close watch on the sky for elusive fast radio bursts (FRBs) - one of the most exciting fields in astrophysics that still is considered a mystery. 

“UTMOST is mainly a ‘transit’ instrument these days, scanning the sky continuously as the Earth turns,” said Molonglo Project Scientist, Dr Chris Flynn from Swinburne University of Technology, who has worked with the Molonglo telescope for many years as part of the UTMOST team.  “The newly installed hardware allows us to see an area about 100 times the area of the full Moon.”

“For the last few years we’ve been searching for and discovering Fast Radio Bursts – some of which have amazing properties – we’ve found some of the narrowest FRBs ever seen, and offering new clues to what causes them (we still don’t know, although magnetars, highly magnetic neutron stars, are a strong candidate),” said Dr Flynn.

Prior to the development of MOST, a number of prototype telescopes were first developed as radio astronomy emerged in Australia, and in particular, in Sydney. Pioneering work by Bernard Mills in 1953-1954 (resourced by the CSIRO at the time) led to the development of the ‘Mills Cross’ in Badgery’s Creek at the Fleurs field station, now not far from the location where Sydney’s second international airport is being developed. 

Much like MOST, its predecessor also featured two long intersecting arms (450-metres in length each), that would sweep and scan the sky at 85.5 MHz, and during early surveys collected data on nearly 2,000 discrete radio sources and structures within the Milky Way’s galactic plane, as well as 49 extragalactic sources. 

At the time, other cross-like telescopes were also built for their own specific purposes as well, such as the 1.4 GHz cross array of small dishes developed by Christiansen, which was used to study the solar disc, and the low-frequency antenna developed by Shain.

But in those days, the world started to see giant radio dish antennas start to flourish, especially across advances made in radio astronomy. Funding and investment also shifted away from the cross-style telescopes to the big dishes, and so Mills joined the University of Sydney’s radio astronomy program - which had ambitions to build a cross-style telescope, but on a larger scale. This was aided by a large investment of funds from the US National Science Foundation. 

Whilst searching for an optimal location to build what would become the Parkes radio telescope, a flat open valley just outside Canberra and not far from the Molonglo river was noted to be of some value, with thanks to surrounding hills that would block out transmissions from the growing capital. However, the designs of the height of the Parkes dish would mean radio frequency interference would only just spill over the hills, and impact observations. So, the site was rejected for Parkes, which then opened an opportunity to build a cross-design telescope, which would remain shielded at their lower height. 

And so, the site was selected as the location to build the Molonglo Observatory, and so began an engineering feat that would last six years and included partnerships between the small group of people associated with the University of Sydney, as well as many industry stakeholders. 

An enormous cross telescope, envisioned by Mills but this time almost four times its size. On the E-W arm, 88 modules and on the N-S arm 177 more. Radio frequency dipoles were built into the arms, forming a meridian transit telescope that featured 2,816 dipoles and 352 waveguides. By May in 1965, the Molonglo Observatory saw its first light and astronomy commenced. 

Then in November of 1965, the Molonglo Observatory was formally opened by Prime Minister Robert Menzies, accompanied by the US Ambassador, members from the US National Science Foundation, Cornell University representatives and many local astronomers. 

“I conducted a heritage survey at Molonglo a few years back,” said Dr Alice Gorman, who is one of the world’s leading space archaeologists and Associate Professor at Flinders University. 

“It’s a whole sensory experience: looking at the Earth and sky through the lacy mesh of the structure, hearing the wind whistling through the long grass, trying to feel the radio pulses coming in from the faraway cosmos through closed eyes.” 

The Molonglo cross was the culmination of the radio astronomy pioneer Bernard Mills’ genius in designing antennas,” she said.

“It’s the third generation of cross-style antennas, and the most sophisticated. Molonglo is one of the instruments which made Australia preeminent in global radio astronomy.”

“There’s a small container of Grote Reber’s ashes at many of the great radio telescopes across the world - for example, Jodrell Bank and Arecibo. Molonglo is one of only three Australian locations to host the remains of this great scientist,” added Dr Gorman.

A number of surveys were commenced and completed using the Molonglo Observatory, at 408 MHz, that required the usage of (what were then) powerful computer systems, including the incorporation of a system that would record the data on magnetic tapes. These surveys detected pulsars, nearby galaxies, planetary nebulae and the Galactic Centre. A good portion of time, roughly eleven years, surveyed the southern sky south of +18 degrees declination, reporting over 12,000 sources in a new catalogue. 

Along the way, a wide variety of astronomers, engineers and students have contributed to the overall knowledge and field of radio astronomy using MOST, many of whom have now gone on to work on projects that feature the latest generation of telescopes like ASKAP, LOFAR and more. But a small cohort still remains, working through as part of the collaboration between the University of Sydney and Swinburne UTMOST program. 

“We have a small staff on-site during the week, and otherwise operate the telescope 24/7 through our remote control systems – we can operate it from anywhere in the world, as is becoming common with many telescopes both radio and optical. Much of the current research work is directly done by students working toward their PhD degrees,“ said Dr Flynn.

In August 1978, the Molonglo Observatory was officially switched off for an upgrade that would change its observing frequency from 408 MHz to 843 MHz, which was when the observatory transitioned to becoming the MOST. As part of this process, and for many years thereafter, the E-W arm did much of the heavy lifting, whilst the N-S arm was decommissioned. 

It was during this time, that the Sydney University Molonglo Sky Survey (also known as SUMSS) was conducted, complimenting the NRAO VLA Sky Survey (NVSS) which covered the northern hemisphere sky. 

But in 2016, MOST would kick start a series of updates that would once again shift its science objectives and turn it into a powerful southern transient search tool. With its large collecting area of 36,000-square metres, it became recognised as a valuable tool to use to search large swathes of the sky in nightly cadence, for the mysterious phenomenon known as fast radio bursts (FRBs). 

These millisecond bursts of high radio frequency intensity have captivated the imagination of astronomers globally since 2007 when they were first discovered in the archival data (dating back to 2001) from the Parkes radio telescope. What makes them so mysterious is that astrophysicists still have no idea what could be causing them, but they are zoning in on a few leading theories (which point to compact remnant objects like magnetars and merging neutron stars). 

But trying to catch one of these things is difficult. One needs to be looking across very large patches of sky, and then have dedicated hardware and software capabilities to extract the signal from the roar of the background noise, making these surveys very computational heavy. And that’s only half the task - trying to localise where the bursts came from (i.e., to pinpoint as small a patch as sky as possible) is also of vital importance, as astronomers are keen to learn about the host galaxies that are producing these things.

And this is where MOST steps up - it scans the sky as it rolls overhead each night, looking for these sharp spikes in the radio regime, now equipped with its new receivers and FRB-dedicated hunting digital systems to process the data. 

To help with these efforts to localise FRBs, a portion of the N-S arm has now also been reactivated with brand new, state-of-the-art equipment, after decades of remaining dormant. Now operating at 830 MHz and at an even higher angular resolution, the new UTMOST has the capability of pinpointing where FRBs are coming from even from the capture of a single burster event. 

The new equipment installed on the N-S arm modules (measuring about 90 meters of the 1600 meters) has been developed with much more modern technology, which translates to having three times the amount of sky coverage and a much higher degree of sensitivity over the E-W arm when compared meter for meter.

“The two arms operating together will give us the capacity to locate where the FRBs we detect come from – we’ll be able to zero in on the host galaxies – meaning we can measure how far away they are, and what types of galaxies cause them!” said Dr Flynn.

As a result, over a dozen FRBs have now been detected using the UTMOST since 2016, including FRB181017 which exhibits some remarkable time sub-structures, and FRB191107, which showcases an extremely narrow pulse profile. 

Additionally, the telescope is timing approximately 170 unique pulsars on a weekly basis, with about 75 observations daily, studying their periodicity, pulse profile shapes, their slow-down rates and keeping a close eye on when these pulsars unexpectedly jump in their timing, in events known as glitches. Recently, the Vela pulsar was observed by UTMOST to glitch. By December 2021, the team announced that they had reached over 10,000 timing measurements from pulsars. 

But the team also sees a future for the telescope at a much closer proximity to Earth. With the rapid escalation of objects like CubeSats being launched into space, as well as the boom of the space sector, thanks to commercialisation - governments and industries are now turning their eye to monitoring activities that occur in orbits around the Earth. 

This is known as space situational awareness, which is the ongoing understanding, monitoring and management of objects in orbit around our planet to ensure that they don’t collide with each other (there are so many these days), as well as for other purposes such as communications and military. 

So after decades of operations, upgrades and a large cohort of Australian scientists, engineers, researchers, the Molonglo Observatory holds a special place in the hearts of many who have come to know this gentle giant. 

From its historical context, it has fortified the foundations of Australian radio astronomy from those early pioneering days in the 1950s and 1960s and continues to deliver on fantastic new discoveries to this day. 

But the telescope has more to offer, and given the opportunity could be one of our most prolific FRB hunters here in the southern hemisphere. 

It also holds a vitally important role, even symbolically, in Australia’s proud and deep radio astronomy history. A connection to a time of pioneering work by the early explorers of this new regime, which first cast their eyes upon the data that came from the radio sky. 

"But most of all it’s our scientific heritage - it’s a fantastic structure which is the visible manifestation of the radio cosmos all around us,” said Dr Gorman.