Astronomers have made an intriguing discovery: a radio signal emanating from the core of 47 Tucanae, a globular cluster located about 13,000 light-years away from Earth. This discovery could potentially indicate the presence of an intermediate-mass black hole, a still-mysterious category in the universe.
Radio observation of the star cluster 47 Tucanae.
At the top, the center of the cluster, marked by a red dashed circle, with a specific area indicated by a white dashed square.
At the bottom, the position of an identified radio source (in cyan) with that of a known X-ray source (in green) and the estimated center of the cluster, taking into account the random motion of objects, illustrated by blue circles.
Credit: Paduano et al.
First spotted by French astronomer Nicolas-Louis de Lacaille in the 18th century, 47 Tucanae is an extremely dense and ancient star cluster. Astronomers used the Australia Telescope Compact Array (ATCA) to capture the most sensitive image ever taken of such a cluster. The very weak radio signal was detected after 450 hours of observation.
The discovery, published on January 16 in
The Astrophysical Journal, points to two main hypotheses. The first is that it could be an intermediate-mass black hole, a type of black hole less massive than supermassive black holes but heavier than stellar-mass ones. While theorized, such black holes have not yet been clearly identified.
The second possibility is that the signal is from a pulsar, a rapidly spinning neutron star emitting beams of radiation across space. A pulsar positioned so close to the center of a cluster would also be a scientifically significant discovery, as it could help in the search for a yet undetected central black hole.
This discovery provides a glimpse into the scientific possibilities offered by the future Square Kilometre Array (SKA) radiotelescopes, currently under construction in Australia and South Africa, with their commissioning scheduled for 2027. Alessandro Paduano, the research team leader and scientist at ICRAR, and his colleague Tim Galvin have emphasized the importance of this discovery made with current technology, anticipating future advancements.
This finding at 47 Tucanae not only broadens our understanding of globular clusters but also raises exciting questions about the nature and presence of intermediate-mass black holes, as well as the role of pulsars in these star-dense environments.