David Malin on astromonical imaging

Jennifer Leonard: How has your experience as a chemist – working with optical and electron microscopy and X-ray diffraction – influenced your work as an astronomical photographer?
David Malin: When I started astronomy twenty-odd years ago, I was very quickly involved with preparing photographic plates for use of the telescope; that’s how the data was recorded in those days, using photography. The things I learned and taught myself as a chemist and X-ray diffraction expert were so useful when I applied them in astronomy because I was detecting radiation and trying to extract from it the maximum amount of information. The underlying principles are the same, but the technologies – telescopes versus microscopes – are entirely different. The specialized hypersensitizing techniques that I used in astronomy – the techniques that make the plates much more sensitive to faint light – are quite complex; they involve some knowledge of chemistry, and I had that already, so it all came together beautifully.

JL: What is the electromagnetic spectrum (EMS) and how does it relate to human vision?
DM: The electromagnetic spectrum is the full range of radiation that permeates our universe and extends from the very short wavelengths – X-rays and Gamma rays – that we normally can’t see from the surface of the Earth, but we can generate from the surface of the Earth artificially – right the way through to the longest, radio waves. In the middle of this range of spectrum is visible light; it’s only a tiny part of the spectrum. And that light illuminates our everyday life and is divided up into the various colors that we see as the rainbow. Human eyes are sensitive to just a tiny part of the electromagnetic spectrum.

JL: How does the EMS factor into our daily lives as human beings?
DM: If we go to the longer wavelengths, beyond infrared, we enter the realm of microwaves – and clearly they’re an important ingredient in everybody’s dinner! There are these practical uses.
But when we’re able to detect [the wavelengths], coming from outer space, they also tell us about the nature of the objects that have emitted them. Not so much microwaves, but slightly longer wavelengths, centimeter wavelengths, which tell us about the nature of the astronomical object that we’re looking at. Beyond these, radio waves are the kind of wavelengths that we use for broadcasting communication. They are received from outer space, too, and tell us about the nature of the stars and galaxies and the physical conditions inside them. Depending on which wavelengths we look at, we learn different aspects of the nature of the natural world beyond the surface of the earth. Shorter wavelengths of light, ultraviolet, are quite an important diagnostic for many astronomical objects. And shorter still, X-rays are a very important way of detecting highly energetic astronomical objects, but this has to be done from satellites in earth orbit; it can’t be done from the ground because, rather surprisingly, X-rays don’t penetrate the atmosphere very well.

JL: How do we extend that narrow band of vision to include the invisible sea of radiation beyond visible light?
DM: For radio waves, we use radio telescopes. These are quite familiar to us as these large dishes – hundreds of meters in diameter – usually steerable arrays that we can point anywhere in space to collect these rather feeble photons from radio waves, and form them into streams of data that we can analyze. At the shorter wavelengths, we use microscopes and X-ray and electronic diffraction equipment to understand the nature of matter. So it’s really a case of using special equipment that’s sensitive to these radiations to be able to detect them and translate them into ways in which our senses can understand them.

JL: What have been the most significant breakthroughs in imaging over the past few hundred years?
DM: The inventions of the telescope and microscope, which were around the same time, were extremely important because they extended the range of human vision, both to the stars and to the smallest things we can see. Their discovery led the basis of much of modern science because we suddenly became aware of a previously invisible world. The simple act of looking through a telescope at the stars and planets triggered a renaissance of thought that changed modern life, absolutely. Probably the next most important thing was the application of photography to scientific imaging, and that happened a hundred and fifty years ago or so; it was a slow process. Photography was discovered in 1839. But by 1880 it was being used in astronomy, and again it displaced the eye from the end of the telescope, because photography was much more sensitive than the human eye, and we could see much farther by using photographic plates. Photographic plates were also a detector of light for microscopes, which detected [light] and recorded it in a way that the eye never could. Photography was also instrumental in the discovery and exploitation of X-rays and was deeply involved in the discovery of radioactivity. Many profound aspects of physics were first explored by means of photography.
The most recent development that, again, is revolutionizing the way in which we look at the world is the charged couple device, the solid state CCD, which we find in digital cameras and more.

JL: What sort of impressive imaging devices are at work today at both the very small scale and the grandest of scales?
DM: In the realm of the small, there are detectors that are used on the synchrotrons, which are devices that accelerate tiny particles to enormous velocities and crash them into targets; the atomic particles of those targets are scattered around in a very distinctive way. The scattering patterns, observed by special detectors (once known as bubble chambers), tell us about the nature of the particles themselves. At the other end of the scale, the Hubble Space Telescope has been making beautiful pictures of distant galaxies with distinctive arcs around them. These arcs tell us that those foreground galaxies have gravitational fields and that they are bending light from more distant galaxies – which means that the galaxies themselves are acting as huge cosmic lenses, creating arc-like, distorted images of much more distant galaxies that we could not see otherwise. These arcs represent the edge of our adventure at the moment in discovering the dimension of things in the natural world.

JL: Is there anything beyond the EMS?
DM: Radiation permeates the solid stuff that we call the world around us and tells us about it in all sorts of ways. The electromagnetic spectrum is so enormously huge: it covers a range of 1026 in wavelength. I just can’t imagine anything beyond it.

JL: How can gravity aid in our quest to image the universe?
DM: It does play a role in imaging the universe, as I said before. However, its essential role is driving the universe. The stars, for instance, are held together by gravity, which compresses the core of stars so that they are dense and hot. This in turn drives the nuclear reaction within them, making the stars shine. But imaging gravity itself is an entirely different thing. Gravity waves are thought to be so enormously long and photons of gravity so weak that they cannot be imaged. But there are proposals to build telescopes to detect gravity waves, which will be generated when massive bodies such as black holes collide at enormous distances in the universe.

JL: What do you feel is the driver behind our ever-expanding ability to make visible the invisible?
DM: Curiosity. It’s human nature to try and understand the world around us. We used to see through our telescopes a range of mysterious fuzzy objects and stars and all sorts of things in space. Now we know that these are galaxies and clusters of stars. None of this knowledge is of any commercial use, but it enriches our intellectual lives. It gives us a scientific framework within which we can discuss all kinds of philosophical ideas about the nature of the universe in which we live.

David Malin is a retired photographic scientist-astronomer based in Australia.