After depleting its hydrogen fuel, a star dies in a violent explosion, ejecting masses of dust, gas and heavy metals into its galaxy. This material is the bane of astronomers trying to work out the rate of expansion of the universe by observing later generations of supernovae, or exploding stars.
Particles in the interstellar medium interfere with light from supernovae, skewing measurements of the objects which are critical to calculating the rate of expansion of the cosmos, says Bradley Tucker, a PhD candidate at the Australian National University’s Mount Stromlo Observatory in Canberra. He is studying the chemical composition of galaxies ranging from 1 billion to 8.5 billion light years away. His results will enable scientists to factor the effect of the interstellar medium into their calculations.
He is a member of a team, led by Brian Schmidt, renowned for Nobel-prizewinning research published in 1998 that challenges the assumption that the rate of expansion of the universe was slowing down. The research suggested that the recession of the galaxies is in fact accelerating. It had big implications for views on the fate of the cosmos – would the universe expand forever or collapse in a big crunch as gravitational attractive forces overcame the force of the Big Bang 13.7 billion years ago?
The ANU team, which Tucker joined in 2005, wants to improve the measurements, centred on the comparison of the spectra of light from nearby and remote supernovae. “The chemical composition of the galaxy affects our measurements of the supernovae,” says Tucker. “If we can account for it, we will be able to get the errors down in the measurements.” He expects to be able to generalise the results from the galaxies he is observing to all galaxies of the same age. He will use ANU’s new SkyMapper 1.3-metre-diameter optical telescope at Siding Spring, near Coonabarabran in northern NSW. He is also using data from the Hubble Space Telescope, the Keck Observatory in Hawaii and facilities as far afield as Chile and the south-west of the US.
Tucker has a BSc in physics from the University of Notre Dame, Indiana. He also holds a BA in philosophy and theology from that institution, and is interested in the philosophical dimensions of cosmology. “We come to a point in science in which we can calculate as much as we can almost to the beginning of the universe but then it gets very abstract,” he says. “The Big Bang is mind boggling.” He was attracted to ANU by its formidable international reputation in astronomy and astrophysics.