What is the best evidence we have for black holes?

For 20 years astronomers have studied the detailed motions of 100 individual stars at the centre of our galaxy around a mysteriously empty region known as Sagittarius A*. these orbits imply that there is a huge source of mass of over 4 million Suns cramped into a region not much bigger than our Solar System… [Here we] see no extra light, certainly nothing close to a million Suns' worth. they represent a pivotal turning point in our understanding of nature: they are regions of space where time itself comes to an end. they form as an inescapable consequence of einstein’s general theory of relativity, and their discovery and confirmation represent a huge success for physics. [the] most important aspect of black holes is that they go beyond even relativity – they predict a region of infinite density and pressure, the singularity, where the laws of physics will cease to exist. today physicists interpret this as a sign that the theory of relativity is incomplete.

Black holes are difficult to detect because of their very nature

Dr Asa Bluck is an astronomer at the University of Victoria, Canada