The hole picture

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Because of the very definition of black holes — no light escapes them and falling objects get infinitely faint when approaching — it is impossible to ever prove that they exist. However, electromagnetic and gravitational-wave observatories have now ‘seen’ black holes. Datasets from these observations, released in late 2018 and 2019, give important hints about the environment, origin and growth of black holes.

Key advances

  • GRAVITY combines four telescopes to form the equivalent of a telescope of 130 m diameter. It has observed luminous material extremely close to the black hole at the centre of our galaxy.

  • The Event Horizon Telescope combines radio telescopes in different continents, equivalent to a detector as big as our planet. This has been used to observe the surroundings of the black hole at the centre of the Messier 87 galaxy, revealing a dark core surrounded by a luminous halo.

  • The latest full LIGO–Virgo data release contains 11 events, 10 of which involve black holes.

  • All observations are consistent with general relativity and predictions for black holes, but the coming years will bring more insights.

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Fig. 1: ‘Seeing’ a black hole.


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The author is grateful to Ana Sousa for the image and is indebted to E. Berti, P. Cunha, K. Destounis, F. Eisenhauer, M. C. Ferreira, J. Grover, C. Herdeiro, D. Hilditch, J. P. S. Lemos and F. Vincent for important feedback.

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Correspondence to Vitor Cardoso.

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The author declares no competing interests.

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Gravitational Wave Events application: https://apps.apple.com/us/app/gravitational-wave-events/id1441897107

ESA ACT BH visualization tool: https://www.esa.int/gsp/ACT/phy/Projects/Blackholes/WebGL.html

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