Ancient universe relic: most sensitive radio image of star relic captured by astronomers

The most sensitive radio image ever of an ancient star cluster has been taken by astronomers and captures the second brightest globular cluster in the night sky – known as 47 Tucanae.

A previously undiscovered radio signal from the centre of the cluster was also detected by the scientists. Astronomer Dr Arash Bahramian, from the International Centre for Radio Astronomy Research (ICRAR), Australia, said star clusters are an ancient relic of the early universe.

He explained: “Globular clusters are very old, giant balls of stars that we see around the Milky Way. 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 image was created from more than 450 hours of observations on CSIRO’s Australia Telescope Compact Array (ATCA). It is the deepest, most sensitive radio image ever compiled by any Australian radio telescope.

Radio waves from celestial objects like planets and stars travel through space just like light, and radio telescopes can intercept them, and they can often be converted into pictures, creating radio images. The cluster can be seen with the naked eye and was first catalogued in the 1700s, but seeing it in detail allowed astronomers to discover a previously undetected incredibly faint radio signal at the centre.

Lead author Dr Alessandro Paduano, from ICRAR’s Curtin University node, said the detection of the signal was an exciting discovery and could be attributed to one of two possibilities.

He said: “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. 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. According to the findings, published in The Astrophysical Journal, the technique used for the ultra-sensitive image could help future radio telescopes detect some of the faintest objects in the universe.