When the main fragment of the comet Shoemaker Levy crashed into Jupiter in 1994, it caused a media frenzy on Earth, while on Jupiter it caused a fireball that leapt hundreds of kilometres above the planet’s surface and ripped a hole in its atmosphere bigger than Earth itself.
The world was gripped by the event, but the only radio astronomer at the University interested in observing it was Professor Richard Hunstead. “The others thought it was boring solar system stuff,” he says from his office in the Physics Building of the University of Sydney where he has worked for more than 50 years. “Once upon a time I would have said the same thing since a lot of my work has been looking at far distant objects.”
To give a sense of the distances, Hunstead mentions in passing, megaparsecs. One parsec is 31 trillion kilometres. A megaparsec is one million of those.
The question for Hunstead in 1994, was whether the collision would affect Jupiter’s radio emission. As influential as Hunstead has been in optical astronomy, he is also internationally recognised for his work in radio astronomy.
Radio waves can travel further than light because they are less affected by absorption from space dust and our atmosphere. Where an optical telescope sees a patch of space as empty, a radio telescope might reveal a far distant galaxy.
As a relatively young branch of astronomy (it only emerged in the early 1930s), there’s still a lot to learn and Hunstead has contributed some important insights. At a time when the mainstream believed that radio sources observed at low radio frequencies were constant in brightness, Hunstead went out on a professional limb to say some were strongly variable, in effect they twinkled.
Likewise, colleagues didn’t believe that a fragment of Shoemaker Levy could affect an object as massive as Jupiter, whereas Hunstead had a strong sense that, at least, it had to be tested.
In both instances he was correct, and in the case of the low frequency radio sources twinkling, he changed the accepted wisdom of that whole area of research.
Hunstead’s willingness to take a stand expressed itself early. When he started University on a scholarship in 1960, he remembers himself as a shy and quiet student who was startled by some of the lecturers, particularly the now legendary, cigar-smoking physicist, Harry Messel.
“He was my very first physics lecturer,” Hunstead says. “And a complete bolt from the blue.”
Yet this shy student none-the-less found himself leading a push to update the University’s whole approach to the teaching of experimental physics. “Lots of exciting things were emerging around electronics that the University wasn’t incorporating,” Hunstead says. “So, when I became a tutor later in my studies, I wasn’t only writing lab notes, I was building equipment.”
One piece of equipment that Hunstead helped build was the Molonglo Observatory Synthesis Telescope, a radio telescope located not far from Canberra and still operated by the University’s School of Physics. He was a student when he first encountered it. Now he is its director.
“My task as a PhD student, was to calibrate the telescope,” he says. “But at the time, we didn’t know how to do it.”
The solution was to find a visible counterpart in the sky, then measure its corresponding radio wave position to cross reference them.
When the telescope began observing in 1965, it quickly made its mark. “It allowed us to resolve structures that were previously just blurred,” he says. “That opened up whole new areas of radio astronomy.”
In particular, it uncovered many previously unseen pulsars, which are highly magnetised neutron stars. “Most of the known pulsars at that time were found by the Molonglo telescope,” he says. “By the late 1970s we had found more than all the other telescopes on the planet, combined.”
I wasn’t only writing lab notes, I was building equipment.
For all the radio success, Hunstead would soon find himself looking at the sky in the visible spectrum. In the 1970s the 3.9 metre Anglo-Australian optical telescope was built in Australia. Up to that time, all the large optical telescopes were in the northern hemisphere, so this new eye on the southern sky was an astronomical sensation.
“I desperately wanted to branch out as an optical astronomer,” remembers Hunstead. Very soon he did just that.
He’d become particularly fascinated by quasars, which were the celestial objects he’d used to calibrate the Molonglo radio telescope. A feature of quasars is that they can be seen in the visible spectrum. They are inconceivably powerful and deeply mysterious. Thought to be an evolutionary stage of galaxies, quasars are super-bright objects found at the centres of most galaxies and they’re powered by black holes. While stellar-mass black holes are known for being incredibly dense, quasars are that, but millions of times bigger than a typical black hole, hence their other name – super massive black holes (SMBH).
The forces at work in a SMBH are so enormous they generate temperatures in the millions of degrees and emit enough light to be seen from Earth, though they might be many megaparsecs away. “You can see a quasar at distances where a normal galaxy is dimmed too much to see,” says Hunstead. “And the light has taken so long to reach us, it’s like we’re seeing something of the universe when it was young.”
As the Anglo-Australian telescope came online, astronomers were realising that the best picture of the universe could be drawn using both optical and radio approaches. Taking his extended knowledge of optical astronomy with him, Hunstead went back to radio astronomy and it continues to be his area of specialisation. That and being the astronomy department’s self-admitted “proof reader from hell”.
At the time of this interview, the first ever picture of a black hole had been flashed around the world just the day before; a picture that had been created using information gathered from eight, synchronised radio telescopes.
Hunstead was understandably excited and eagerly absorbing all the information that was circulating. “It’s all knowledge,” he says quietly. “And I admit, I could learn a hell of a lot more.”
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