About thirty kilometres east of the Australian capital Canberra stands a telescope that will soon capture images of the cosmos’s most mysterious phenomena. The Molonglo Observatory Synthesis Telescope (MOST), nestled in the Molonglo Valley, is the largest radio telescope in the Southern Hemisphere and has been scanning the skies for nearly half a century.
Now, the Australian astronomy community have ambitious plans to use this telescope to understand the ‘transient’ Universe, short-lived phenomena that can only be detected through frequent, regular radiofrequency surveys.
But before this can happen, MOST needed to be brought into the 21st Century. After operating for fifty years — a lifetime for any piece of technology, especially one as complex and sensitive as a giant radio telescope — it desperately needed an upgrade, especially to its digital technology.
While its basic structure would remain the same, the revamp to its operational infrastructure would make it capable of churning through the masses of data generated by these surveys.
In 2012, the UTMOST project was conceived to achieve this goal when the telescope’s operators, The University of Sydney, joined forces with Swinburne University of Technology, the CSIRO,Australian National University and Massachusetts Institute of Technology. Matthew Bailes, an Australian Laureate Fellow at the Swinburne Centre for Astrophysics and Supercomputing, took on the task of leading the upgrade of the telescope’s ageing processing system.
1,320 gigabytes a minute
When it was built in the 1960s, the Molonglo telescope discovered some of the most spectacular objects in our cosmos, such as the collapsed cores of once-massive stars, known as pulsars.
Pulsars can be as small as 20 kilometres in diameter, and can spin at up to 700 times each second. Their distinctly pulsatile radiofrequency signature results from the acceleration of particles in their super-strong magnetic fields as they spin.
“It’s fun when you find a pulsar that is spinning 700 times a second; that’s faster than a kitchen blender and yet it’s a star,” says Bailes.
Precisely measuring the pulse rate of these celestial objects has revealed new insights into how gravity distorts the fabric of space-time.
MOST’s long structure was built to overcome the design limitations imposed on parabolic dish telescopes, which can only get so big before they topple over. The telescope has two 800-metre-long half-cylinders stretching east to west. Along its two arms sit 7,744 individual radio antennae that combine their signals to create a concentrated radiofrequency beam.
The upgrade kept this design, but called for a radical overhaul under the hood, installing new signal-processing computers that could sift through 22 gigabytes of data every second, or 1,320 gigabytes per minute.
Early on, Bailes realised the upgrade couldn’t rely on existing analogue systems to combine the signals to form an image — it needed a system that could digitally combine all the signals together.
“I realised that some of the technology we’d developed here at Swinburne could be adapted to do that,” says Bailes.
Anne Green, a professor of astrophysics at the Sydney Institute for Astronomy, in The University of Sydney, says one of the major achievements of Bailes and his team has been to write new software for the telescope to improve data acquisition and signal processing. The upgrades will allow astronomers to observe a large area of the sky 1,000 times a second.
“The powerful supercomputer that Bailes and Swinburne have provided makes this an exceptional telescope for exploring the transient sky with fast and flexible cadence,” says Green.
In the astronomy world, Bailes’ ability to use supercomputers is highly sought-after. In July 2015, he was invited to join an international team awarded $100 million to search for intelligent life elsewhere in the Universe. Bailes’ Australian team will work with collaborators at the CSIRO and the University of California, Berkeley to use the Parkes 64-metre telescope to search for signs of alien transmissions from stars in our Milky Way Galaxy. The pursuit will be part of the most comprehensive search for aliens ever undertaken. Bailes is optimistic about the endeavour because the technology now available to search for signs of intelligent life is superior to that available for the last systematic searches undertaken at Parkes in the 1990s. The project, administered by the Breakthrough Prize Foundation, will scan the skies for signals of life as well as other naturally-occurring astrophysical phenomena, such as pulsars and Fast Radio Bursts.
1,000 snapshots a second
After a five-year hiatus, MOST recently began scanning the skies again. One of its first priorities will be to observe fast radio bursts — very bright, millisecond-long flashes of radio energy first observed just ten years ago.
Only around fifteen of these events have ever been observed by astronomers, some by Bailes and colleagues at Swinburne University. They appear to be happening outside our Galaxy, but no one really knows what causes them.
“There are more theories than there are bursts,” Bailes says. “Some people think that they occur when two neutron stars collide, others think that neutron stars become unstable and collapse into a black hole and they give off little bursts of radio emission when they do it.”
Other theories suggest that they arise when black holes and neutron stars merge, or as an early warning signal of an impending supernova. There is even the suggestion that these bursts might have something to do with the atmosphere of a star that makes them appear further away than they really are.
Once every few weeks
The upgraded Molonglo telescope isn’t yet fully operational, and is currently running at only a quarter of its efficiency. But Bailes is already excited about what might come when it reaches its full potential.
“The detection rate is a strong function of efficiency so we haven’t been running long enough to find a fast radio burst, but we’re hoping that soon we’ll be finding one every few weeks.”
The Molonglo telescope is also continuing its long tradition of contributing to the field of pulsar study. Bailes spends much of his time studying these spinning neutron stars as a kind of hot-house for strange gravitational behaviour.
“Neutron stars are very tiny so they can get in very close proximity to each other, which means that they travel very quickly around each other and they allow us to test gravity in ways that we can’t normally do,” Bailes says.
These rapidly waltzing pairs might even answer a puzzle left by Einstein. The great physicist predicted the existence of a peculiar type of gravitational ‘radiation’ called gravitational waves — but no one has seen one yet. In theory, pulsar pairs should emit these waves. While astronomers can’t detect the waves themselves, they can detect the changes to the orbits of these spinning pairs as tiny amounts of energy carried off by the gravitational waves.
“These waves are mysterious and difficult to detect but they actually cause the orbit of the neutron star to shrink by one centimetre per day, which might not sound like much, but using the upgraded telescope we can measure the position of neutron stars so accurately that we can even begin to see that effect.”
Given the fundamental importance of this work, there’s little doubt it will be time well spent.
Measuring a one-centimetre change in orbit from halfway across the Galaxy, or capturing a millisecond-long burst of radiofrequency energy somewhere in the Universe, requires extraordinary technology that is only found at very few locations around the world.
In recognition of UTMOST’s unique capabilities, the collaboration has elected to make all the data generated by the Molonglo telescope available instantly to researchers anywhere in the world, which represents a big shift in the way astronomers communicate with each other.
“Usually what you do is you build a telescope and you keep all the data secret and you do a grand magic reveal at the end,” Bailes says.
“But with these fast radio bursts, if we did that, by the time we gave people the information it would be worthless because the thing would have faded away so we decided we’d give away any event immediately.”