What is a Black Hole?

A black hole is a region of space where the force of gravity is so extreme, everything – including light – cannot escape its pull. There are millions of ‘stellar’ black holes in the universe, formed by the collapse of giant stars. ‘Supermassive’ black holes, are far bigger, and are found at the centre of almost every galaxy.  We do not yet know how they form, however Albert Einstein predicted the existence of black holes in his theory of General Relativity over one hundred years ago. Einstein stated that objects with a massive gravitational force, such as a black hole, would cause a distortion in space-time and bend the path of light. The observations of the EHT team have confirmed this prediction.

The centre of a black hole is called the ‘singularity’ – a dimensionless point of infinite density and enormous gravitational force. (Scientists are not entirely sure that singularities actually exist, but they do present a problem with the maths used to describe black holes). The edge of a black hole is called the event horizon. It is the boundary beyond which nothing can escape, not even light. Around the black hole swirls the ‘accretion disk’ – super heated gas and dust that emits radio waves, heat and huge x-ray flares. The EHT team were able to detect and measure the radio waves emitted by M87. A supercomputer was then employed to take all the measurements and turn them into the now famous image.