The finding is an exciting confirmation that black holes can 'flicker', moving from maximum power to switching off over, in cosmic terms, short periods of time.
"For 20 years astronomers have suspected that such a significant outburst occurred, but now we know when this sleeping dragon, four million times the mass of the sun, awoke and breathed fire with 100 million times the power it has today," said Professor Joss Bland-Hawthorn, lead author of an article on the research to be published in The Astrophysical Journal, from the University's School of Physics.
Ahead of publication, Professor Bland-Hawthorn will unveil the research at the international Galaxy Zoo science conference on 24 September in Sydney.
"It's been long suspected that our Galactic Centre might have sporadically flared up in the past. These observations are a highly suggestive 'smoking gun'," said Martin Rees, Astronomer Royal, who was one of the first scientists to suggest that massive black holes power quasars.