The answer is Sagittarius A* (Sgr A*) (pronounced Sagittarius A-star).
Sgr A* is 4.3 million times more massive than our Sun.
Sgr A* is located about 25000 light years away from Earth.
Black holes themselves are not visible by definition but the vicinity of black holes are very active. These areas can be imaged.
“In fact the light that we see from Sgr A* does not come from within the black hole but instead comes from gas which is falling into the black hole. As gas falls into Sgr A* it creates a thick puffy disk known as an accretion disk. Accretion disks are very energetic environments with strong magnetic fields which drive turbulence and heat up the gas as it spirals into the black hole. This hot excited gas emits photons at a variety of wavelengths which are then lensed by the gravitational field of the black hole. The details of accretion mechanisms are still a very active area of research, and we hope that the images the EHT will take of the extreme environment of Sgr A* will help us understand them.” – EHT
The EHT (Event Horizon Telescope) scientists are still processing data to produce the first direct image of the event horizon of Sgr A*.
During their historic announcement of the first ever direct image of a black hole (event horizon) they showed the image belonging to the super-massive black at the center of M87 galaxy (a giant elliptical galaxy in the constellation Virgo). For this heroic effort the 2020 Breakthrough Prize in Fundamental Physics was awarded to the Event Horizon Telescope collaboration. The $3 million prize was shared equally among 347 scientists co-authoring any of the six papers published by the EHT on April 10, 2019 (papers can be found here).
The super-massive black hole in the center of M87 is 6 billion times more massive than our Sun and it is 50 million light years away from Earth.
I recommend the following articles for further reading:
Ethan Siegel, “10 Deep Lessons From Our First Image of a Black Hole’s Event Horizon”
Dennis Overbye, “Darkness Visible, Finally: Astronomers Capture First Ever Image of a Black Hole”
Matt Strassler, “A Ring of Controversy Around a Black Hole Photo”
processed image of the event horizon of the supermassive black hole at the center of M87 galaxy (source: EHT)
The image above is a false-color image showing the intensity of radio waves originating from the vicinity of the event horizon.