Template:POTD/2019-12-21

Picture of the day

A black hole is a region of spacetime exhibiting gravitational acceleration so strong that nothing – no particles or even electromagnetic radiation such as light – can escape from it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of the region from which no escape is possible is called the event horizon. Although the event horizon has an enormous effect on the fate and circumstances of an object crossing it, no locally detectable features appear to be observed.

This picture is a photograph of the shadow of the supermassive black hole at the centre of the Messier 87 (M87) elliptical galaxy in the constellation Virgo, as captured on 11 April 2017 by the Event Horizon Telescope, a planet-scale array of eight ground-based radio telescopes, a collaborative effort by scientists from over 20 countries; the photograph itself was released on 10 April 2019. As a black hole is a completely dark object from which no light escapes, its shadow is the next best alternative to an image of the black hole itself. The event horizon, from which the telescope takes its name, is around 2.5 times smaller than the shadow it casts and measures just under 40 billion kilometres (25 billion miles) across.Photograph credit: Event Horizon Telescope