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The globular cluster 47 Tucanae

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NASA / ESA / UPI Photo / IMAGO

Astronomers have found evidence of an intermediate-mass black hole in the globular cluster 47 Tucanae. In the most accurate radio image of the cluster of stars to date, they identified a faint source of radio rays in the center, they write in the journal "The Astrophyscial Journal".

47 Tucanae is the second brightest globular cluster in the Milky Way, about 15,000 light-years from Earth. More than a million stars are clumped together in a comparatively small space. In good conditions, the cluster can be seen with the naked eye from the southern hemisphere.

450 hours of observation

The international team of experts at the Australian radio telescope ATCA, a network of six large antennas, targeted the globular cluster from a location northwest of Sydney. 450 hours of observation were necessary to produce the high-resolution image, according to a statement from the International Centre for Radio Astronomy Research.

The source of radio waves could be a medium-mass black hole. In black holes, an extremely large amount of mass is compressed into a small space. Intermediate black holes are significantly lighter than their massive siblings at the center of galaxies such as the Milky Way; they may be formed by the collision of individual stars.

Pulsar as a further explanation

"It has long been suspected that medium-mass black holes occur in star clusters," said Alessandro Paduano, an astronomer at Curtin University in Australia who was involved in the study, according to the release. "So far, however, there are no clear indications of their existence."

In addition to a black hole, another explanation for the weak radio signal is conceivable: a pulsar. Pulsars are rotating stars made of neutrons. A pulsar would also be an interesting discovery, Paduano continues. "It could be helpful in the future search for a black hole."

Globular clusters belong to relics from the early universe and therefore provide insights into its formation. With a radio telescope called Ska, which is currently under construction, the researchers hope to be able to study the clusters of stars in more detail in the future.

When Ska goes into operation at its two sites in Australia and South Africa, it is expected to become the most sensitive radio telescope in the world. The current measurement gives a foretaste of what "will be possible with the next generation of radio telescopes," said astronomer Arash Bahramian, who was also involved in the study.

MSK