Hubble constant wins Professor prestigious prize
Media Release, Thursday 4 June 2009
Measuring the size and age of the universe has won University of Melbourne Professor Jeremy Mould and his international colleagues the prestigious 2009 Gruber Prize for Cosmology, announced by the Peter and Patricia Gruber Foundation overnight in the United States.
Professor Jeremy Mould of the University of Melbourne’s School of Physics shares the prize worth $US500,000 with Wendy Freedman, Director of the Observatories of the Carnegie Institution of Washington in Pasadena, California, and Robert Kennicutt, Director of the Institute of Astronomy at the University of Cambridge in England.
The award recognizes the astronomers’ leadership in the definitive measurement of the Hubble constant, which explains the expansion rate of the universe since its beginning, thus connecting the universe's size with its age.
The findings of the Hubble Space Telescope Key Project in 1999 have since been confirmed and recognized as one of the most important measurements in astronomy.
The expansion rate of the universe has been hotly debated since Edwin Hubble’s original discovery in 1929 that galaxies were rushing away from each other at a rate proportional to their distance, i.e. the farther away, the faster the recession.
“We were able to greatly improve the accuracy of the measurement, “says Professor Mould. “We are receiving this prize now because a lot of additional work has confirmed our findings, allowing the prize givers to be very confident of our results.”
During 10 years of research the Mould, Freedman and Kennicutt team used the Hubble Telescope to observe 18 galaxies out to 65 million light-years. They discovered almost 800 Cepheid variable stars, a special class of pulsating star used for accurate distance measurement. Although Cepheids are rare, they provide a very reliable "standard candle" for estimating intergalactic distances. The team used the stars to calibrate many different methods for measuring distances.
They ultimately measured the Hubble constant at 72 km per second per megaparsec (a megaparsec is 3.26 million light years, and a light year is about 5.9 trillion miles) with an uncertainty of 10 percent. This means that a galaxy appears to be moving 160 thousand miles per hour faster for every 3.26 million light-years away from Earth.
On this information they were able to estimate the age of the universe to be 13 billion years old. The universe's age is calculated using the expansion rate from precise distance measurements, and the calculated age is refined based on whether the universe appears to be accelerating or decelerating, given the amount of matter observed in space.
The resolution of the decades-long debate about the value of the Hubble constant is enabling scientists to answer fundamental questions about the universe.
“What the Hubble constant also does is to tell us the density of the universe. This controls the future evolution of the universe, which is accelerating,” says Professor Mould.
Measuring the Hubble constant was one of the three major goals for NASA's Hubble Space Telescope before it was launched in 1990.
Professor Mould’s current work continues in further clarifying the reliability of the Cepheid variable stars as a measurement of light and distance of galaxies.
Freedman, Kennicutt, and Mould will receive the Prize on August 4, 2009, at the opening ceremony of the International Astronomical Union's General Assembly in Rio de Janeiro, Brazil.
Jeremy Mould is a professorial fellow at the University of Melbourne, working in the astrophysics group of the School of Physics.
Previous appointments include Director of the National Optical Astronomy Observatory (NOAO) in the US, Professor of Astronomy at the Australian National University, Director of the ANU's Research School of Astronomy & Astrophysics, and Professor of Astronomy at the California Institute of Technology's Palomar Observatory.
Professor Mould has been strongly connected with the Hubble Space Telescope program. He was co-Principal Investigator for the Hubble Space Telescope Key Project on the Extragalactic Distance Scale. The goal of that project, completed in 1999, was to measure the Hubble Constant, and thus the age and size of the Universe.
He is author of more than 400 research papers in professional journals.