PREVIEW

A global consortium of astronomers has crafted the most sensitive radio image to date of a globular cluster, an ancient congregation of densely-packed stars. The focus of this unparalleled image is 47 Tucanae, the second brightest globular cluster visible in the night sky. The achievement is credited to a team spearheaded by the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR) in Western Australia.
Published in The Astrophysical Journal, the research not only presents this extraordinary image but also unveils a previously unidentified radio signal emanating from the cluster's core.
Dr Arash Bahramian, an astronomer from ICRAR’s Curtin University node, said that globular clusters represent ancient remnants from the early universe.
“Globular clusters are very old, giant balls of stars that we see around the Milky Way,” he said. “They’re incredibly dense, with tens of thousands to millions of stars packed together in a sphere.
“Our image is of 47 Tucanae, one of the most massive globular clusters in the galaxy. It has over a million stars and a very bright, very dense core.”
The featured image of 47 Tucanae, among the galaxy's most massive globular clusters, showcases over a million stars and a remarkably radiant, densely-packed core.
The exceptionally sensitive image resulted from over 450 hours of observations using CSIRO’s Australia Telescope Compact Array (ATCA) on Gomeroi Country, marking it as the most profound and sensitive radio image ever compiled by an Australian radio telescope.
Dr Alessandro Paduano, lead author from ICRAR’s Curtin University node, expressed the excitement surrounding the discovery of a faint radio signal at the cluster's centre, previously unnoticed due to its subtlety.
The signal's origin presents two possibilities, according to Dr Paduano.
“The first is that 47 Tucanae could contain a black hole with a mass somewhere between the supermassive black holes found in the centres of galaxies and the stellar black holes created by collapsed stars.” he said.
“While intermediate-mass black holes are thought to exist in globular clusters, there hasn’t been a clear detection of one yet.
“If this signal turns out to be a black hole, it would be a highly-significant discovery and the first ever radio detection of one inside a cluster.”
The second possible source of the signal is a pulsar—a rotating neutron star that emits radio waves.
“A pulsar this close to a cluster centre is also a scientifically interesting discovery, as it could be used to search for a central black hole that is yet to be detected.” Dr Paduano said.
Dr Tim Galvin, a research scientist with CSIRO and co-author, added: “This project has stretched our software to its limits, in terms of both data management and processing, and it has been really exciting to see the wealth of science that these techniques have enabled.”
“Alessandro’s research represents a culmination of years of research and technological advancements, and ATCA’s ultra-deep image of 47 Tucanae represents just the beginning of the discoveries that are yet to come.”