A mysterious radio signal has been detected coming from the heart of an ancient star cluster in the Milky Way, 14,500 light years away from the Sun: it could have been emitted by a pulsar, a rapidly rotating neutron star, or by a medium-sized black hole , a rare type of black hole never observed before and which would therefore represent an important discovery.
The signal is described in the study published in the journal The Astrophysical Journal and led by the Italian Alessandro Paduano, of the Australian International Center for Radio Astronomy Research, at the Australian Curtin University.
The researchers spotted the mysterious signal while examining the globular cluster called 47 Tucanae with the Australia Telescope Compact Array, a radio telescope operated by the Australian Government Agency for Scientific Research.
Globular clusters are ancient groupings of stars scattered across the Milky Way.
47 Tucanae, in particular, contains more than a million stars in a sphere with a diameter of only 120 light years, and is the second brightest cluster in the sky.
Thanks to 450 hours of observation, the authors of the study obtained the most detailed radio image of the cluster, also discovering the unusual signal coming from its interior.
“Although intermediate-mass black holes, the missing link between those generated by supernova explosions and the gigantic objects observed at the centers of galaxies, are thought to exist in globular clusters, none have yet been clearly identified,” he says Paduano.
“If this signal turns out to be a black hole – adds the Italian researcher – it would be a very significant discovery and the first radio detection of a black hole within a cluster”.
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