Research Press Release

Astronomy: Rare event caused by black hole pulling apart star observed

Nature Astronomy

December 1, 2022

Observations of a rare tidal disruption event (TDE) — bursts of energy released when a star is torn apart by a supermassive black hole — are reported in papers published in Nature and Nature Astronomy this week. The findings may improve our understanding of the properties of black holes at cosmological distances.

TDEs can provide an opportunity to study how supermassive black holes grow by accumulating (or accreting) matter. When a star is pulled rapidly towards a black hole, it can be disrupted and its material can fall onto the black hole’s accretion disk. In some cases, accreted material generates powerful jets of matter, and in very rare cases TDEs can lead to the production of a relativistic jet, travelling close to the speed of light, but these events are rare and poorly understood. The new observations reported in Nature and Nature Astronomy shed more light on these rare events.

Igor Andreoni, Michael Coughlin and colleagues and Dheeraj R. Pasham and colleagues report the detection of AT2022cmc: a transient astronomical event releasing large amounts of energy. The observations, made in the optical range and at other wavelengths using multiple telescopes, are consistent with emission from a luminous jet from the violent disruption of a star passing too close to a massive black hole. These observations, particularly those in the X-ray regime, indicate the extreme energies involved, and rapid brightness changes and the long-lived nature of the entire event are hallmarks of a rare relativistic jetted TDE, one of only four reported to date. Whereas most detected TDEs originate in the nearby Universe, this event came from a galaxy some 12.4 billion light years away and was only visible from Earth because of its exceptional brightness.

By modelling the event, Pasham and colleagues favour a scenario where a star similar in size and mass to the Sun was disrupted by a relatively low-mass black hole. They note that the inferred magnetic field is unusually low contrary to the conventional theory that such highly relativistic jets require high magnetic fields. Andreoni and colleagues conclude that their findings confirm that around 1% of TDEs have relativistic jets, corroborating previous predictions of the rareness of such occurrences.


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