Professor Ken Freeman
Professor Ken Freeman is Duffield Professor of Astronomy at the Australian National University (Research School of Astronomy & Astrophysics, Mount Stromlo Observatory) in Canberra. He studied mathematics at The University of Western Australia and theoretical astrophysics at the University of Cambridge, followed by a postdoctoral year at the University of Texas and a year as a fellow of Trinity College, Cambridge. He returned to Australia in 1967 as a Queen Elizabeth II Fellow at Mt Stromlo Observatory, and has been there ever since.
His research interests are in the formation and dynamics of galaxies and globular clusters, and particularly in the problem of dark matter in galaxies: he was one of the first to point out (in 1970) that spiral galaxies contain a large fraction of dark matter. For his current research, he uses optical and radio telescopes in Australia and the USA, and also observes with the Hubble Space Telescope and large optical telescopes in Spain, Chile, and Hawaii. He has written about 750 research articles, and a book on dark matter, and was named by ISI in 2001 as one of Australia’s most highly cited scientists.
Professor Freeman was the 2009-2010 UWA Institute of Advanced Studies Professor-at-large.
The interview below was conducted in 2010
What got you into Astronomy?
I got in astronomy entirely by accident. I was interested in maths, I was good at it, and I did my maths degree here at UWA, but the emphasis here was mostly in aerodynamics. UWA had a very good applied mathematics group here at the time I was going through, but the key guy got sick and died at the age of 39 which was very sad: he was really the mainstay of the group.
So, we did a lot of aerodynamics. At the end of my second year of undergraduate work I went to work for a summer at the weapons research establishment in Salisbury in South Australia, where they had a good aerodynamics group, a practical experimental group. I had a lot of fun there and it just happened that I saw on the notice board a notice about vacation scholarships at Mt Stromlo Observatory which even at that time they were doing, we still do them, and I thought “oh, that looks interesting”. So I wrote off to Bart Bok at Stromlo and said “please tell me more, I’d be interested” and he wrote back very quickly, an effusive two page letter about how great astronomy is, and I thought “OK, sounds cool.” So I went there the following summer and had quite a good time. I went back again at the end of my honours, and that got me on the road really, because I could have finished up in anything. It’s just luck that I got into astronomy.
You’ve spent the majority of your career at the Australian National University but of course you visited many institutions and places around the world. Where would you say is the best place that you’ve worked?
Well, it must be Mount Stromlo, because I keep coming back there and like all of us I’ve had lots of opportunities to go and work other places, even on a permanent basis, but I keep on coming back to Stromlo. It’s a good place to work. But as you say, I’ve worked in a lot of places and I can’t think of anywhere that I have really not been pretty happy, I think I could work almost anywhere.
There’s a lot of good places around, each place has it’s own style, but I guess I must like Stromlo best because I keep on going back there.
It’s a very good atmosphere, there’s almost no internal fighting, and that’s quite unusual. Mostly there are factions in almost any group, and that’s just part of life, but it’s just a bit more of a hassle. Somehow we avoided that.
Perhaps part of the reason, it’s quite a big observatory, it’s probably over 100 people, , there’s like 25 faculty and typically 25 to 30 students and then a bunch of postdocs on top of that. But we’ve deliberately stayed non-departmental: often people want to set up their own little departmental empires, but we’ve really resisted ever doing that. So there’s a single budget and it really has stopped a lot of the internal tensions that you see in some other places which have departmentalised.
What’s the most fun thing that you think you’ve done, or the thing that you’re most proud of that you’ve achieved as part of your career?
I’ve had a lot of graduate students, I’ve had 54 PhD students and I’m pretty proud of them, most of them have done pretty well. Short of the research things that we’ll talk about in a moment, it’s probably what I’ve done with students.
Everyone is different, and you’ve got to kind of tune your style to each one because what works for one doesn’t work for another. I’ve also had eight or ten postdocs working with me, and they’ve mostly survived. They’re fun too, again they’re very different, some people come out of a PhD really not as independent researchers and they need another few years to get them really rolling, and others come cracking out of PhD school all set to go and you have to try and evaluate which situation each one’s in and give them as much support as they need but no more, and let them run as much as you can. That’s fun.
What are you working on at the moment?
I usually have quite a number of things on the run at once. I’m working quite a lot on extragalactic planetary nebulae. Planetary nebulae are stars that are just in the process of dying, and in this process they become very luminous, actually very luminous in one particular emission line, and that makes them quite easy to find and we can actually find these single stars out to enormous distances, out to a hundred megaparsecs, which is a huge distance, far, far, far outside our galaxy and they’re wonderful traces of very diffuse collections of stars. For example, in clusters of galaxies and in the space between galaxies you have actually quite a lot of stars, but the density of stars is very low; they’re just stars that we think have been ripped off the galaxies, they’re flying around in space unattached to a galaxy.
But you can’t see these stars from their surface brightness, they’re much too diffuse, but you can see the individual stars as they go through this planetary nebula phase. This phase only lasts about 10,000 years, but there’s always a few stars passing through this phase at any one time, and the nice thing about them is that you can pick them up because of this emission line, at huge distances, and you can also measure their velocities from the spectra, so you can actually find them and see how they are moving. We’ve been working on planetary nebulae for a long time, using them as probes of various kinds of faint star populations, intracluster stars, outer parts of elliptical galaxies.
Another thing I’m working on a lot at the moment is the bulge of our own Galaxy. our Galaxy has a central bulge of stars, and nobody quite knows what it represents. Some people think it’s something that formed quite early in the life of the Galaxy, when galaxies were merging and falling into our own galaxy building it up. Other people think “no, that’s not the right explanation”, it comes from the disk of our Galaxy, which goes unstable and puffs itself up in the middle and each one of these different ways of producing has got a particular signature that we can measure, and so we’re just in the process of measuring those. We’ve now got spectra of about 30,000 stars in the bulge of our own galaxy and we are analysing them for how they’re moving and what their chemical properties are like and try and work out just how this bulge actually formed. I’m doing this work with one of our students and some colleagues, it’s a nice project.
And then the really big thing that’s coming up in the next couple of years is a new instrument on the Anglo Australian Telescope, it’s called HERMES and I’m the project astronomer for it with a colleague. We will get high resolution spectra of about 1.2 million stars with this instrument. The goal is to recognise groups of stars that form together, using their chemical properties. You need the high resolution spectra to measure a lot of details about the chemical properties and that’s our goal. That project should start late in 2012. Once that starts, we’ll probably go for about five years on this project.
When you’re measuring 1.2 million stars you have to have automation at a level that people have never done for this kind of observation. For chemical work, people have always measured one star at a time, one element at a time, but we can’t do that so we’re building automatic pipelines with as little human intervention as you possibly can have.
I’m involved in another big project at the moment, which is to acquire spectra of about half a million stars, though not at such high resolution. That project’s now getting close to the end. It involves about 50 people around the world, and we have actually looked at every single one of 500,000 stellar spectra between us. Just to make sure that nothing crazy is happening.
Really, the looking was done by three or four people. Half a million stars sounds an awful lot, but one gets pretty good at looking, and particularly at recognising things that slip through the computer net one way or another. But when you look at these things with an experienced eye, you can spot these problems very quickly.
The whole field of Galactic astrophysics is going through an enormous resurgence at the moment, partly due to ideas that my colleague and I have been pushing in the last five or six years. There’s a lot of new interest in Galactic astronomy and a huge amount of money and effort going into it, not just in Australia but all over the world. It’s a real boom time.
We have opportunities in our galaxy to do observations which we cannot possibly do in other galaxies and certainly that we have no hope of ever doing in galaxies at the edge of the Universe. If you want to understand how galaxies form, you have a choice. You can either go and look at the galaxies as they form, out at huge redshifts – they are very faint and you need huge telescopes and you can’t measure much detail because they’re too faint. Or you can say “all right, our galaxy went through a formation process itself at high redshift”. The oldest stars in our galaxy formed at redshift of six, seven, eight – find those stars and study them. It’s a approach that we really got going, and it’s called near field cosmology as opposed to far field cosmology. For nearby stars you can measure a vast amount of chemical details, and exactly how everything is moving. So these approaches are complementary, and there’s a lot of effort going into this new approach.
You’ve been published in Nature and many other prestigious journals, what is your favourite published work? What is your favourite paper you’ve published?
I published a paper in 1970 that has had a lot of citations. It was really the discovery paper for dark matter in galaxies, and I’m pretty pleased with that. That discovery sort of happened a bit by accident.
The main point of the paper was to work out what the shape of the rotation curve of a typical spiral galaxy would be. For some reason nobody had ever done that, it’s something you can do analytically, you don’t even need a computer. So I worked this out analytically and then compared those rotation curves with some of the galactic rotation curves that were just starting to become available.
It was very early days for radio astronomy, particularly for radio synthesis astronomy. It was already pretty clear that some of the nearer galaxies that one can study were not rotating in the way that you would predict from this rather simple rotation curve and that was straight away a pointer that there has to be a lot of dark material in outer parts of the galaxy. That got the whole thing going.
That took nearly a decade before the dust settled. Some people thought there was dark matter, some people though there wasn’t a problem, but by about 1978 it was pretty clear that there was a big problem. It’s like most of these so-called paradigm shifts, they take a while. Some people love the new concepts, some people resist them. So, I was very pleased with that.
There’ve been a few others. One of my colleagues and I found the first clear evidence that globular cluster stars are not chemically identical. People thought the stars in globular clusters were all chemically identical and we found in one cluster where that wasn’t the case. That again started a large industry which is still going strong, now about 30 years later.
You’ve done significant research into galaxies and dark matter, what do you think we’ll find out in the future once the next generation of telescopes are completed?
I think with dark matter it won’t be the optical or radio telescopes that sort this one out for us. We’ve already got a pretty good idea how dark matter is distributed, strong and weak lensing studies are a tremendous help for some classes of galaxies we weren’t able to study before, and I think the basic concepts are in already. What we don’t know is what this dark stuff is, and that’s going to be a challenge.
I don’t know quite from where that break is going to come. It might come from the physics laboratories. A lot of people are doing direct detection experiments, trying to find different kinds of potential dark matter candidates. They assume that dark matter is in the form of axions, neutralinos or whatever and then they do experiments looking for these things.
These are very tough experiments, because these particles don’t interact much with anything. They pass straight through the Earth and out the other side without even noticing it. But, there is a small possibility that any one can be detected. People have been working on this now for decades, with no success yet, but that’ll come. It’s in some ways parallel to gravitational waves. People have been looking for them for a long time. The techniques are getting better and better, and sooner or later they will either find them or they will be able to say “well, they are not there.” It’ll be the same with dark matter.
The other potential break for dark matter (I’m talking about dark matter here, not dark energy) will be annihilation experiments. The way this works is that if the dark matter is in the form of quite massive weakly interacting particles (100 giga-electron volt masses or more) they can interact and annihilate. When they annihilate, they can produce gamma radiation. This gamma radiation will be pretty faint. But there are some large gamma ray telescopes that are already online, and more to come, some in space, some on the ground. One of the exciting places to look will be in the class of galaxies called dwarf spheroidal galaxies, which have a very high density of dark matter.
For reasons to do with the expansion of the Universe, the smallest galaxies are the ones that form out of the Universe first, and they come out at the density of the Universe at that time. So, some of these small galaxies that formed very early, they are actually very dense in dark matter and we can measure those high densities using techniques we already have available.
So you can work out how much annihilation radiation you might get from these things, and you can get more radiation from a small dense thing, that a big fluffy one. Not only are they dense but we know from theory that dark matter haloes are not nice and smooth, they’re full of lumps and these lumps increase the probability of detection of gamma rays in some cases by very large factors like 10, 50.
There’s a pretty good chance we will see this annihilation radiation if the dark matter particles are neutralinos. That won’t come from optical or radio telescopes, it will come principally from the gamma ray telescopes.
Dark energy is another story. I don’t know so much about dark energy. There the big telescopes are potentially helpful. The new optical and radio telescopes will contribute to lensing experiments and acoustic oscillation experiments. A lot of that is happening already. I don’t know where that’s going to go. So far the dark energy looks like a cosmological constant, w=-1, with no surprises yet. But we’ll see.
You’re Professor-at-large for UWA’s Istitute of Advanced Studies. What is the best part of that role?
The Institute does masterclasses. When I first heard about these I thought “How is that ever going to work.” But they actually work very well, they’re a lot of fun. I’ve done a couple of these, and I’ll do one more this year. I’m going to go to somebody else’s masterclass next week. They are quite interesting, you have some very relaxed and informal discussions.
They run for a whole day. I’ve been quite impressed with that format. The lead speaker talks for perhaps half an hour or an hour on their particular thing, and then there are questions and discussion, and other people talk about what they’re doing and then there’s questions about that. It’s a nice leisurely day of research discussion, deliberately kept down to an informal group of ten or fifteen people, a mixture of students, postdocs and faculty. I’ve really enjoyed them.
If you had unlimited funds for research, what would you do with them?
I think I’d follow Kavli’s example: he endows institutes all over the world. I’ve just been at one in Beijing, that’s been going for a couple of years. They have an endowment to keep the place going in the long term. They hire a bunch of people to do research, and this does seem to work very well.
Equipment’s very important, but so are people in research institutes. In a way, ICRAR is this kind of institute. You have to be careful about who you hire but the goal is to get a bunch of good people together. It needs a nucleus of people who are permanent and hold the place together and hold the corporate memory, and the other people come and go on maybe five year timescales. Five years is a good time, three years is a bit short, and you get a mixture of young, mid career, older people.
They don’t need to be big institutes, if you can get say 20 researchers plus the support people that you need for a group like that, it’s really very powerful. I think if I had a lot of money to splash around, that’s what I’d do with it.