Scientists expected to release landmark image of black hole

FILE PHOTO: The world's largest milimetric telescope (50 metres in diameter) is seen in the Sierra Negra Volcano, at an altitude of 4,600 m (15,000 ft.), which lies between the states of Puebla and Veracruz in Mexico, June 20, 2011. REUTERS/Henry Romero

WASHINGTON (Reuters) - An international scientific team is expected on Wednesday to unveil a landmark achievement in astrophysics - the first photo of a black hole - in a feat that will put to the test a pillar of science: Albert Einstein's theory of general relativity.

Black holes are phenomenally dense celestial entities with gravitational fields so powerful no matter or light can escape, making them extraordinarily difficult to observe despite their great mass.