Have we actually seen a black hole out there? By "seen" I mean "recorded a em-spectrum image of gravitational lensing caused by object believed to be black hole".

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    $\begingroup$ Possible duplicate of How are black holes found? $\endgroup$ – SE - stop firing the good guys Feb 13 '16 at 18:25
  • $\begingroup$ My question is not "how we can find black holes?", but rather "have we already?". It's related, but distinct. $\endgroup$ – Koder Feb 13 '16 at 18:33
  • $\begingroup$ @RobJeffries Please elaborate. Should you mean "no, we did not record a image of gravitational lensing of object believed to be a black hole", this should be an answer, not an comment. If however you meant "no, this is not an distinct question" elaboration is still welcome. $\endgroup$ – Koder Feb 13 '16 at 19:02

The answer was no prior to 10 April 2019. There were no resolved images at any wavelength of black holes or black hole candidates that demonstrated their lensing effect.

There were of course lensing images due to massive objects that probably have black holes at their centres (e.g. Courbin et al. 2010 and see below), but that is not the same thing.

A quasar acting as a gravitational lens

A quasar acting as a gravitational lens - Courbin et al. (2010)

All this has changed with the release of a reconstructed millimetre-wave image of the supermassive black hole at the centre of M87.

The image below, obtained by the "Event Horizon Telescope" (a global interferometer) is formed by intense light from accreting matter being lensed by a 6.5 billion solar mass black hole. The dark circle is known as the "photon shadow" and is about two times the size of the black hole event horizon. The bright ring is caused by the lensing of light from around and behind the black hole. It is thought to be asymmetric and off-centre because of the black hole rotation.

Event Horizon Telescope Image of M87 black hole

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    $\begingroup$ As of today, this answer is no longer correct -- or, rather, it doesn't tell the whole story. $\endgroup$ – S. Imp Apr 10 '19 at 17:01
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    $\begingroup$ nice edit! SO EXCITING! $\endgroup$ – S. Imp Apr 10 '19 at 18:06

While the original post inquires specifically about gravitational lensing, I'd like to suggest that this is not the only criteria for "seeing" a black hole. Clearly, since no light can escape from a black hole, the actual hole itself cannot be seen. However, there are a variety of epiphenomena that can be observed, and gravitational influence on other celestial bodies (e.g., stars) can certainly be observed.

The European Southern Observatory (ESO) released a video of the center of the Milky Way galaxy made from 20 years of observations of this area by the NACO instrument on ESO's Very Large Telescope in Chile. This seems to me like extremely compelling evidence that an enormous black hole exists at the center of the Milky Way.

As for gravitational lensing, Space.com reported just such an image attributed to Courbin, Djorgovski, & Meylan. This image may satisfy the exact criteria requested by the OP.

EDIT/UPDATE: This morning (April 10, 2019), the Event Horizons Telescope held press releases on four continents announcing that they have indeed imaged M87*, a black hole of an estimated 6.5 billion solar masses in the Messier 87 galaxy, some 55 million light years away. Strictly speaking, we still cannot see the black hole itself but rather its epiphenomena such as the accretion disk and the turbulence caused by the presence of the black hole. This image, created by very long baseline radio interferometry, is not a photograph in the traditional sense, but rather a false-color image composite generated by converting enormous volumes of radio wave observations with a supercomputer into an image visible to the human eye.enter image description here

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    $\begingroup$ The Coubin image dates to 2010 and is the same as that Rob included. If you read carefully, you will see the gravitational lensing is actually done by the quasar's host galaxy. "By studying the way a quasar magnifies light as a gravitational lens, he said, 'we now can measure the masses of these quasar host galaxies' " $\endgroup$ – James K Jul 31 '18 at 7:42
  • $\begingroup$ While I agree that there are other ways to determine locations of black holes, I was specifically interested in visual images. Light can not escape event horizon, but accretion disk should be visible. As far as I know, best visual representation of black hole we have comes form movie "Interstellar", where a black hole was simulated by specifically written rendering software. $\endgroup$ – Koder Jul 31 '18 at 10:33

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