In April 2010, an unusual party was held under the clear skies of the Namibian desert. It was an international science conference to celebrate the 70th birthday of Professor Ken Freeman, the Duffield Professor of Astronomy at the Australian National University’s Mt Stromlo Observatory, a man regarded internationally as Australia’s most renowned astronomer.
After two years of summer employment at Mt Stromlo, Ken was hooked. He decided to apply for a PhD at Cambridge on the advice of an astronomer he had met at the observatory. What attracted him—and still does—was the scope for problem-solving that astronomy throws up. “It’s you against the Universe.”
Among many other achievements, Ken is perhaps best known for putting “dark matter” on the galactic map. In 1970, he published a paper showing that what we see of galaxies—as stars, gas and dust—is only a small fraction of their mass. The rest is invisible, dark matter. It’s a finding which changed the course of astronomy. But that was only the beginning of his career.
More recently, in 2002, he became a founder of what today is one of the hottest fields of investigation in astronomy, galactic archaeology—determining the age and movement of stars in our own galaxy through analysing their chemical composition. The aim is to work out how galaxies were constructed. And the field has become a major driver in the commissioning of new ground and space-based telescopes.
Now, after nearly 50 years of shaping and changing the human view of galaxies and the Universe, Professor Ken Freeman has been awarded the 2012 Prime Minister’s Prize for Science.
Ken Freeman’s full citation
It all started in 1959 with a flyer on a noticeboard at the-then Weapons Research Establishment in Salisbury, just north of Adelaide. Young Ken Freeman, a student in physics at the University of Western Australia, saw it while working there in the holidays at the end of his second year. The advertisement encouraged him to apply for a vacation scholarship at the Mt Stromlo Observatory near Canberra. When he did so, he was overwhelmed by the enthusiastic two-page, hand written response he received from the-then director, Professor Bart Bok. “This was a man who charmed (then-Prime Minister) Bob Menzies,” Ken says. “He was a real showman.”
In the late 60s, after a post-doctoral fellowship in Texas, Ken was back at Mount Stromlo, studying galaxies. He started thinking about how spiral galaxies, such as our own, rotate. The motion is almost circular, and it’s a tenet of basic physics, dating back to Newton, that in order to have circular motion you need an inward force towards the centre of the circle to keep things from flying off in a straight line. In a galaxy, that force would be provided by the gravitational attraction of the matter in the galaxy—the stars, gases and dust.
But when Ken did the numbers, they didn’t even begin to add up. To prevent it from splitting apart, a rotating spiral galaxy would need far more mass—at least 10 times more, Ken calculated later—than had ever been seen. In 1970, Ken published a paper to that effect. The recognition of the missing mass, dubbed “dark matter”, changed the way astronomers perceived galaxies and the Universe. The paper started a decade of dispute about whether dark matter really existed, and a hunt for ways of detecting and measuring it. Dark matter is now generally accepted throughout astronomy.
In the 40 years since that time, Ken Freeman has continued to work on problems to do with the structure and movement of galaxies, and his pile of achievements has continued to grow. The most precise evidence about dark matter still comes from studying the rotation of galaxies. That data usually originates from tracking the motion of atomic hydrogen in galaxies using radio telescopes. Ken and his colleagues developed the analyses still used to break down these observations into components for stars, dust, gas and dark matter.
While it has long been known that the luminous, visible matter in galaxies is normally deployed in the shape of a flat disc, Ken has been interested in trying to work out the shape of dark matter in galaxies. Another question on which he is working that is still not settled, is the ratio of dark to luminous matter in the parts of our galaxy closest to Earth—near the Sun, for instance.
Some of his achievements have given him particular pleasure. As part of the work in recognising dark matter, Ken surveyed information on the properties of many galaxies, to determine how varied galaxies were. But he noticed an astonishing regularity of one property, the brightness of the surface of disc galaxies was always the same, no matter what their size. This law provides fundamental information about how the discs of galaxies were assembled in the early Universe. It is now known as the Freeman Law. “I’m pretty pleased with that,” Ken says.
Another achievement of which he is particularly proud came out of discussions in the late 80s with Joss Bland-Hawthorn—then a young post-doctoral fellow, now a professor at the University of Sydney—at a conference at Princeton University. They like to call it near-field cosmology, although the more popular term is galactic archaeology.
Most stars in galaxies form in groups or clusters of between about ten thousand and a million stars. But these clusters do not typically persist over time. As the stars begin to shine they blow off gas and lose mass. After about 10 million years, the clusters have lost so much mass that there is not enough gravitational attraction to hold them together, so individual stars begin to wander off. By the end of three or four galactic rotations of about 200 million years each, they are spread far and wide throughout the galaxy. But because they all formed at the same time in the same place they all have the same ratio of elements in their makeup. It’s like a fingerprint.
Professors Bland-Hawthorn and Freeman realised that such a chemical tag could be used to determine the age and movement of stars that formed in the same cluster, and could provide strong evidence for how galaxies are constructed. Ultimately, tracking the stars within our own galaxy, the Milky Way, could give us a lot of knowledge about the structure of galaxies in general. But that enterprise called for instruments that could make it possible to record and analyse the spectrum of light of up to a million stars.
Since publishing their ideas in 2002, the field of galactic archaeology has taken off all over the world. For instance, the $1 billion European Space Agency telescope, GAIA, to be launched in 2013, has been equipped with instruments to pursue galactic archaeology. And the Australian Astronomical Observatory is just completing the construction of an instrument, HERMES, which can gather the spectra of 350 stars in our galaxy simultaneously and send them for automatic analysis for about 30 elements. The hope is that it can tag about a million stars in the five years after testing is completed. It is scheduled to begin operations in 2014. The project will involve about 40 astronomers, mostly Australians.
It is with such collaborations, and particularly in interactions with students, that Ken has left an enduring mark. Already he has supervised and mentored more than 50 PhD students, including five of the ten Australians selected by NASA as Hubble Fellows, regarded as one of the world’s most prestigious post-doctoral positions. “It’s a lot of fun, working with students. When they come in, their basic knowledge is zero, and they learn on the job. After three and a half to four years, they know as much as you do—and they’re quite ready to tell you so.”
With HERMES about to start testing, doing the rounds of six grandchildren in Canberra and others elsewhere, travelling to conferences, a bit of bird-watching and furniture-making, and making observations with optical and radio telescopes, Ken Freeman shows no sign of slowing down. Almost like the Universe, he just keeps expanding his horizons.
1965 PhD (Applied Mathematics and Theoretical Physics), University of Cambridge
1962 Bachelor of Science with First Class Honours (Mathematics), University of Western Australia
2013 Matthew Flinders Medal, Australian Academy of Science (AAS)
2012-2018 Member, Scientific Advisory Board, Max Planck Institute for Extraterrestrial Physics, Garching
2010 Member, Hubble Telescope Multi-Cycle Treasury Programs Time Allocation Committee
2009-2012 International Astronomical Union Special Nominating Committee
2008-present Project Astronomer for HERMES spectrometer, Anglo-Australian Telescope (AAT)
2008 Yale Astronomy Department Review Chair
2008 Johann Wempe Award, Astrophysical Institute, Potsdam
2004-2009 Member, Gemini Wide Field Multi-Object Spectrograph Science Working Group
2004 Antoinette de Vaucouleurs Lecture and Medal, The University of Texas
2003 Blaauw Professor, The University of Groningen
2003 Centenary Medal, Australian Government.
2002 Associate of the Royal Astronomical Society
2001 Tinsley Professor, The University of Texas
2001 Ranked number five of Australia’s 35 most cited scientists by ISI
1999 Dannie Heineman Prize, American Institute of Physics and American Astronomical Society
1998 Fellow of the Royal Society of London (FRS)
1997 Visiting Fellow, Merton College, University of Oxford
1995-1997 Scientific Advisory Committee, Indian Inter-University Centre for Astronomy and Astrophysics
1995-2002 Receiving Editor, “New Astronomy”
1994 Oort Professor, University of Leiden
1993-1996 Large Telescope Working Group of the National Committee for Astronomy, AAS
1993 Distinguished Achievement Award, University of California Institutes
1990 Marc Aaronson Memorial Prize Lecture, The University of Arizona
1989-1993 Australia Telescope Steering Committee
1988–2003 Distinguished Visiting Scientist, Space Telescope Science Institute
1988-1992 UK Schmidt Telescope Advisory Committee
1984 & 1988 Visiting Member, Institute of Advanced Study, Princeton
1981 Fellow of the Australian Academy of Science (FAA)
1976 Senior Scientist, Kapteyn Laboratory, University of Groningen
1975-present Organising Committees, International Astronomical Union (Commissions 28, 30, 33 & 37). Variously acting as President and Vice-President
1972 Pawsey Medal, Australian Academy of Science
1967-present Queen Elizabeth Fellow (1967), Fellow (1970), Senior Fellow (1974), Professorial Fellow (1981), Professor (1987), Duffield Professor (2000), Mount Stromlo and Siding Spring Observatories, The Australian National University
1966 McDonald Post-doctoral Fellow in Astronomy, The University of Texas
1965-1969 Research Fellow of Trinity College, Cambridge University
Header image: Ken Freeman (credit: Prime Minister’s Science Prizes/Bearcage)