Reverend Robert Evans, star gazer and supernova hunter
With just an amateur’s telescope and his memory, Rev Robert Evans has astonished scientists with his ability to spot cosmic death.
“That’s where I look,’’ says the Reverend Robert Evans, tilting his head at the tall windows behind him that open onto a narrow deck and a garden filled with trees. If you go out to that deck and gaze upwards at a patch of sky between the big gum trees studding the garden, there’s little to see now but a twist of smoke from the burning off they’re doing further down the hill. During the day it’s just a shred of cobalt between the boughs, but at night that strip of heaven becomes Evans’ playground, his classroom, his history book.
For more than four decades, Rev Evans, 80, has traversed the night sky, hunting death. By day, as circuit minister with the Methodist church, he would worship life with his flock in the Uniting Church in the Blue Mountains and write books about evangelical history. But when the sun went down and the constellations were in the right position, he’d take his telescope out to that little deck and hunt dying stars. This nightly quest was not just for any stars but for supernovae, the elusive, ancient titans of the skies, the exploding stars that helped create the universe and tell us its history.
And until very recently, when technology caught up and surpassed Evans’ talents, he was the king of supernova hunters, finding more by visual means than any other astronomer, professional or amateur, in the world. He did this by the incredible feat of memorising 1500 galaxies and spotting when something different was happening in any one of them. Even today, with a record 42 under his belt, he has been surpassed by only four people — and all of them have used sophisticated computer technology to find their supernovae. “I still hold the record for visual discoveries,” he tells me proudly as the sky starts to fade.
A supernova is a cataclysmic event that occurs when a giant star explodes. There are two types of explosion mechanisms. One occurs when a “white dwarf” — a small, very dense star — orbiting around a companion star and stealing its hydrogen through gravity, swells into a supergiant. When a white dwarf reaches 1.4 solar masses (a solar mass is equal to the mass of our sun) it triggers a detonation from the inside, creating an eruption so bright that the supernova may appear brighter than its entire galaxy. This is a Type 1a supernova.
The second, Type 2, involves a star 10 to 20 times the mass of our sun that runs out of nuclear fuel, triggering a cataclysmic implosion and, soon after, a violent explosion that releases the energy of 100 billion suns. They are the most dramatic events in the universe, like a trillion hydrogen bombs going off at once. If they occurred anywhere near Earth, we would be obliterated. But, fortunately, they don’t occur that often and not too close us. In a galaxy the size of the Milky Way, supernovae happen only about once every 50 years. And when they do occur, they are usually millions of light years away. Their distance and the brevity of their appearance make supernovae almost impossibly elusive: by the time their light reaches us, for the few weeks before they fade they are just a slightly brighter twinkle than all the millions of other stars up there. The only way you know they are there is to recognise that there is something among all the billions of stars in our sky that wasn’t there before.
This is what Bob Evans excels at. By memorising the position of every star in “his” 1500 galaxies, he can detect — with nothing more sophisticated than his phenomenal memory and his telescope — when a change in a galaxy takes place. To help understand what a feat this is, there is no better description than in Bill Bryson’s A Short History of Almost Everything, in which he devotes a chapter to Evans and his legendary skill. “Imagine a dining-room table covered in black tablecloth and someone throwing a handful of salt across it. The scattered grains can be thought of as a galaxy. Now imagine 1500 more tables like the first one … each with a random array of salt across it. Now add one grain of salt to any table and let Bob Evans walk among them. At a glance he will spot it. That grain of salt is the supernova.”
Evans’ memory is so extraordinary that Oliver Sacks compared him to a savant in his book An Anthropologist on Mars and it has made him a legend in the world’s community of astronomers. “There is no one to match him in terms of memory,” says Stuart Ryder of the Australian Astronomical Observatory. “I don’t even know anyone who could remember the location of so many galaxies. But as soon as Bob puts his eye to the eyepiece he can tell if something has changed. Even today, with robotics, we aren’t there yet. We’re working hard to train computers to do that, but we aren’t yet at the stage when they are as good as someone like Bob and his eye and his brain.”
Evans seems embarrassed, or perhaps bored, by such praise and brushes it off. “Ah well, practice helps,” he says when I bring it up. “I haven’t got a photographic memory. I suppose I’m good at visual observations and patterns.”
Despite his modesty, Evans’ influence on astronomy has been extraordinary. He was awarded the Order of Australia in 1987 for his contribution to science and Ryder says that without him, the world’s understanding of the universe would not be as advanced as it is today. “Because he was doing all this important work in the 1980s, he helped get us further along the path of discovery, helped accelerate our understanding of supernovae. He was a true pioneer.”
Evans’ great advantage over professional astronomers is, paradoxically, the fact that he is an amateur with only modest equipment. Professionals must book time on the great telescopes of the world and the size of those telescopes means their movement is limited to only a small area of sky at a time. But out on his back deck of his Hazelwood home Bob could swing his telescope quickly and easily to observe many more galaxies than the professionals.
Evans is retired now and since having a stroke earlier this year he has been unable to lug his bulky 12-inch telescope out to his deck for a night of supernova hunting. Besides, his 16-inch telescope — on which are marked, like notches on a belt, the supernovae he has discovered and their dates of discovery — is at the Linden Observatory, elsewhere in the Blue Mountains. Until recently he could view up to 600 galaxies in any lunar month as long as the conditions were right, noting the stars’ positions, checking for changes. On a typical night, when the moon wasn’t too bright and the constellations were in favourable positions, he could observe 55 galaxies in an hour; 120 an hour in the so-called “Virgo Cluster”, when the galaxies are closer together.
You’d spend, what, a few minutes on each galaxy? “Oh no, a couple of seconds,” he responds. “You point the telescope in the right spot, find the galaxy, spend half a minute looking at it then move on. You operate by constellation, by which part of the sky you can see. They’re like old friends now, the galaxies,” he adds. “Particularly when you find a supernova in one. I found three in one galaxy, NGC 1559, the last in 2005.” (NGC stands for New General Catalogue, a record of deep-sky objects started in 1888.)
The names — or at least the numbers — of hundreds of galaxies and supernovae skip off his tongue like the names of his children. He says he’s not that great at recalling things outside astronomy; it’s just the stars and the galaxies that he can retrieve in an instant. His father, a botanist, was the same; he knew the botanical names of more than 1000 species of plants that grew around Sydney and the Blue Mountains. It was his father who first got him interested in astronomy, taking him onto the laundry roof of their home in Eastwood, Sydney, to point out the constellations. When he was about 14, Evans’ optometrist brother made him his first microscope out of a couple of rolls of paper and a spectacle lens. It wasn’t much better than the naked eye but it focused his interest. After leaving school, he bought, for £15, an optical system that consisted of a mirror and tube. “It wasn’t a proper telescope, just an old eyepiece from a microscope, but I could sit on the floor and twist my neck to look through it.” This was the start of an interest that would obsess him for over half a century, even as his professional life took him away from science to God and the church.
Evans started seriously stargazing in the 1950s but it wasn’t until the 1970s that he began hunting supernovae. Before he joined the church he worked at Angus and Robertson and found a book on astronomy that had a chapter on supernovae. Scientists only began to understand supernovae in the 1930s, when an eccentric Swiss physicist at the California Institute of Technology named Fritz Zwicky and his colleague Walter Baade coined the term, hypothesising that they were the transition of super-massive stars into small, incredibly dense neutron stars. Zwicky theorised that the collapse of the star would result in a massive explosion, or supernova. To support his hypothesis Zwicky began searching for supernovae using photographic plates rather than telescopes. By the time Evans turned his basic telescopes upwards, it was really just the two of them, one in each hemisphere, hunting the giant explosions.
Evans goes into his cluttered study, where his 12-inch telescope sits surrounded by books, files and photographs of supernovae, and retrieves the book that started it all. The Galactic Novae by Cecilia Payne-Gaposchkin, first published in 1957, cost him a week’s wages but it told him about the few supernovae that had been found at that time. “The fact that not much was known about them got me interested,” he says. “When I looked at how bright they were I came to the conclusion that I could try to find one myself if I had a telescope that was eight or 10 inches. I had this thing I had bought which was a five-inch. Five-inch telescopes have very low magnification so it had to be a fairly bright galaxy before you could see it.”
At this point, it would have been impossible for the young Bob Evans to go supernovae hunting: to spot one in a galaxy millions of light years away would require a much more powerful instrument. (Supernovae have been observed by the naked eye only four times in recorded history: 1006, 1572, 1604 and, most recently, in 1987, when a supernova exploded in the Large Magellanic Cloud, the galaxy next to ours.) So Evans concentrated on learning about the galaxies: where they were in the sky and where the stars were within them. “If there had been a supernova in some of these galaxies I might have seen it but very likely they would have been too far away, too faint, so I wouldn’t have realised they were there. But I was able to remember what they [the galaxies] generally were like,” he says, with understatement.
In the late 1960s and early 1970s he and his wife Elaine moved to a church in Lake Macquarie, NSW, where the dark skies were perfect for supernova hunting. But Evans realised that even if he did discover a supernova he could never prove it because he didn’t have the photographic backup to check the appearance of galaxies before and after the emergence of that telling flare of light.
Finally, in February 1981, he discovered his first supernova. It had been unusually cloudy for weeks but one night he noticed a faint star that appeared in a position different from that indicated on the charts. Was this his eureka moment? He laughs. “Well, it was and it wasn’t. It was fairly obvious to me that it was a supernova but whether you risk reporting it … you have to have the verification first.” Evans had a friend, Tom Cragg, at the then Anglo-Australian Observatory, who had agreed to double-check whatever he found. “But he was frightened of making a mistake which would bring discredit. The star was a supernova Type 2 which stays there for a while so he got one of the professional astronomers to have a look at it with one of the main telescopes and then we were able to report the discovery.” Within 15 days, he and Cragg had discovered their second supernova. “I was at Tom’s place for a few days and it happened in the driveway of his home. In that instance we made the discovery and had it verified and reported within a couple of hours. It was the first amateur discovery of a Type 1, so that showed what visual observation can do.”
As Evans increased the number of galaxies he searched, the findings kept coming. He found four supernovae in 1983 and another four the following year, bringing his total to 10 before he moved onto a larger telescope, a 16-inch he’d got with a grant from the CSIRO. From 1995 to mid-1997 he also had limited access to the 40-inch telescope at Siding Spring Observatory at Coonabarabran, in NSW’s central west, which resulted in another three visual supernovae discoveries and four more from photographs at the observatory. By 2005 he had made 40 discoveries; his last, his 42nd, was 10 years ago. “2008AW, I think it was called. It was found by one of the professional groups but I found it before them. I was in the country at a friend’s place but we couldn’t go online to check it. But I rang the people in Boston to tell them it was there so I got my name tacked on as a discoverer.”
The “people in Boston” are astronomers at the Harry Potteresque-sounding Central Bureau for Astronomical Telegrams in Cambridge, Massachusetts, which collects and verifies information on cosmic discoveries. Here are kept the records of all Evans’ discoveries, each one a triumph he would duly celebrate with a bottle of cider.
To the non-astronomically minded, 42 discoveries in nearly four decades may not sound like much of a feat. But it wasn’t just the number for which he is so respected. As Ryder has pointed out, it’s partly thanks to Evans and his discoveries that astronomers have been able to understand and track the history of our universe. His discovery of a Type 1a supernova in 1981 was followed by another 14 of this type, which are fundamental to our understanding of the size of the universe and the rate at which it is expanding. Because they almost always have the same luminosity, their light growing at the same rate to maximum brightness before fading again, cosmologists use them as “standard candles” to measure distance across the universe; the fainter the stars, the further away they are. These standard candles were used by Saul Perlmutter, Brian Schmidt and Adam Reiss and their teams to prove that the universe is expanding at an accelerated pace, a discovery that earned them the 2011 Nobel prize for physics.
“Half of all Bob’s discoveries were Type 1a,” says Ryder. “But back then it wasn’t recognised how important they would be to our understanding of the universe. We thought there were only two types of supernovae but now we recognise there are so many more subvarieties and that’s partly because of the discoveries Bob was making.”
By now Evans has photographs of his supernovae out on the table. Until he takes you through the galaxies, the photographs look almost disappointingly unassuming; a dark spiral and a couple of dots inside them on a white background. But when he shows you that one of the dots is a supernova, you realise you are looking at something remarkable — a death from millions of years ago, before our own beginnings, whose light arrived just in time for Evans to swing his telescope and catch it.
In the 1980s and 1990s Evans discovered other types and subclasses of supernovae that showed cosmologists that not all Type 1 supernovae could be used as standard candles. His discoveries of what became known as Type 1b and 1c supernovae were fundamental as they behave very differently to the 1a. Caused by the core collapse of massive stars, their luminosity is less than that of Type 1a so an attempt to use them as standard candles would skew the measurement of the universe.
In 2001 he discovered a Type 2 supernova in the outskirts of the NGC7424 galaxy in the Grus constellation, about 40 million light years away. The significance of this supernova, called SN 2001ig, is only now beginning to be fully understood. It was a Type 2 but acted more like a Type 1a. Scientists couldn’t work out what caused the star’s sudden loss of hydrogen until Ryder observed radio waves from the site of the explosion that indicated the presence of another star. He realised that SN 2001ig actually came from a pair of giant Wolf-Rayet stars — stars that are about 20 times the mass of our sun; the second star had siphoned off the first star’s hydrogen, its nuclear fuel, causing its cataclysmic death.
It took another 15 years before the effects of the explosion had finally cleared. Ryder and his colleagues were able to book time on the Hubble Space Telescope and turn it toward the supernova in 2016, seeing for the first time the surviving star.
A decade after he found his last supernova, Evansis being left behind by science. Although he still holds the record for visual discoveries, he can’t compete with the technology. “It’s such a big industry in universities and observatories, where they have equipment that can cover the whole sky in one night,” he says. “They can find supernovae that I would never see in 100 years. By the time a supernova is bright enough for me to see it, they would have been able to find it a week earlier.”
He’s pragmatic about this but sadder that his stroke has curtailed his nightly strolls among the constellations. His 12-inch telescope lies redundant in his study although his occupational therapist is planning to rig something up so he can once more take it onto his deck without having to carry it. But he’ll never have the joy of turning his big 16-inch telescope to the skies again. “My strength has gone,” he says. “I have no balance.”
Evans is silent for a while, considering the end of this huge part of his life. It’s terribly sad, I say. “It is sad,” he agrees softly. “But you don’t live forever, not in this world.”
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