25 April 2002
Australian team "sets the Universe's clock"
NASA will announce tomorrow the results of a unique international effort aimed at settling the controversy regarding the age of the Universe.
These new results show that the Universe must be over 12 billion years old and is unlikely to be any older than 14 billion years.
Teams of astronomers at five universities around the globe, including Swinburne University of Technology in Melbourne, have spent the past year sifting through data generated by the famous Hubble Space Telescope.
The study focused on ancient burnt-out stars - called white dwarfs - lurking within Messier 4, a star cluster orbiting our Milky Way Galaxy in the constellation Scorpius.
By pushing Hubble's capabilities, the team has cleanly identified the oldest individual stars in the oldest of the Galaxy's clusters. Independent of many of the contentious assumptions that have plagued previous age-dating techniques.
Professor Brad Gibson of Swinburne's Centre for Astrophysics & Supercomputing heads the Australian effort, "We have been looking at the oldest and faintest white dwarfs (burnt out stars) in our Milky Way. A bit like a pathologist measuring body temperature to determine time of death, we can use the temperature of a burnt-out star to work out the star's age."
These dim white dwarf stars are 12 to 13 billion years old and are so feeble, they are less than one-billionth the apparent brightness of the faintest stars that can be seen by the naked eye.
Dating how long ago the 'Big Bang' occurred has been something of a holy grail for astronomers. Professor Gibson's earlier Hubble research estimated the age of the Universe - indirectly - at 13 to 14 billion years, based on the rate of expansion of space. But astronomers have since sought independent age-dating techniques to cross-check these conclusions.
Conceptually, the new age-dating observation is elegantly simple. White dwarfs cool down at a predictable rate - the older the dwarf, the cooler it is, making it a perfect "clock" that has been ticking for almost as long as the Universe has existed.
____________________________________________________________________________________Contacts:
Mark Heaney or Heather Crosling, Media Liaison Tel (03) 9214 5123 Mobile 0416 174 962
Email: hcrosling@swin.edu.au
Professor Brad Gibson (03) 9214 8036 mobile 0438 358 709 or Email: bgibson@astro.swin.edu.au
Backgrounder -
· Professor Brad Gibson heads the Cosmology & Galaxy Formation Group at Swinburne Unversity, the fastest growing astronomical research group in the country. Two of his team (Dr Daisuke Kawata and PhD student Mr Chris Brook) have been working with him to understand the theoretical implications of the data from Hubble. In particular, they are undertaking highly sophisticated computational simulations of galaxy formation, using the Supercomputing facilities at Swinburne and the Victorian Partnership for Advanced Computing. Specifically, they are now looking at the data to understand the role that mysterious 'dark matter' plays in the formation of our Galaxy. It has been calculated that dark matter makes up 90% of the Universe's mass but very little is known about it. Dark matter can not be seen because unlike stars, it does not give off light.
· Prof Brad Gibson uses observational and theoretical methods to study how galaxies are formed and the expansion of the Universe.
· Using white dwarfs has been recognised as more reliable than age-dating the oldest stars still burning by nuclear fusion, which relies on complex models and calculations about how a star burns its nuclear fuel. White dwarfs are easier to age-date because they are simply cooling, but the trick has always been finding the dimmest and hence longest-running "clocks."
· As white dwarfs cool they grow fainter, and this required that Hubble train a steady gaze on the ancient globular star cluster M4 for eight days over a 67-day period. This allowed for even fainter dwarfs to become visible, until at last the coolest - and oldest - dwarfs were seen. This 8-day time allocation was the largest ever awarded to anyone working outside of the Hubble Space Telescope host institute.
· The globular cluster M4 was selected because it is the nearest to Earth, so the feeblest white dwarfs are still bright enough to be picked out by Hubble.
· Globular star clusters are among the oldest objects in our Galaxy. They can easily be observed through amateur telescopes.
· Globular clusters contain mostly low-mass stars that are tightly packed together. If you were on a hypothetical planet in the middle of a globular cluster, like Messier 4, you would be in a perpetual twilight cast by the light of thousands of nearby stars.
· More than 150 globular star clusters are known to be associated with the Milky Way Galaxy. Each cluster contains hundreds of thousands stars.
· In 1928, Edwin Hubble's measurements of galaxies made him realise that the Universe was uniformly expanding, which meant the Universe had a finite age that could be estimated by mathematically "running the expansion backward." Edwin Hubble first estimated the Universe was only 2 billion years old.
· Uncertainties over the true expansion rate led to a spirited debate in the late 1970s, with estimates ranging from 8 billion to 18 billion years.
· In 1998 Professor Gibson and his Hubble Space Telescope Key Project colleagues broke this impasse by announcing a reliable age for the Universe, calculated from a precise measurement of the expansion rate. The picture soon got more complicated when astronomers using Hubble and ground-based observatories discovered the Universe was not expanding at a constant rate, but accelerating due to an unknown repulsive force termed "dark energy."
Media note : Spectacular colour pictures and video clips of the globular cluster M4 are available at the Hubble website - http://news:46cluster@cauldron.stsci.edu/prweb/inprogress/2002/10/ - Look for 'Dating white dwarfs in M4'.
