What are 'mini' black holes?

'The simplest black holes are objects with a singularity in the centre and that are surrounded by an ' event horizon ',' explains Cigdem Issever of Oxford University's Department of Physics. 'Once something comes closer to the black hole than the radius of the event horizon, it is not able to leave: even light can't escape and so the name 'black hole' was given to these objects by John Archibald Wheeler back in 1967.' A hole in the Sun - Producing black holes turns out to be about mass (energy): squeeze mass into a sphere with a radius equal to what's known as the ' Schwarzschild radius ' - a threshold beyond which gravity causes an object of a certain density to collapse in on itself - and a black hole will form. 'In fact the size of the Schwarzschild radius is directly proportional to the amount of mass that is squeezed in, as well as being directly proportional to the strength of gravity,' Cigdem tells me. 'For example, in order to form a black hole out of our Earth, you would need to squeeze its mass into a sphere about the size of a marble (radius 8.9 mm). By comparison the Schwarzschild radius of the sun is about 3 km.' 'If we replaced our Sun with a black hole of the same mass, surprisingly, not much would change in our solar system. The planets' orbits would stay the same because the gravitational field that the black hole would produce would be exactly the same as that of the Sun. Although, admittedly, the solar system would be a bit dark and cold!' 'I became interested in them as a particle physicist back in 2003 because extra dimension models predicted that they may be produced in high-energetic cosmic rays and, if so, even in particle accelerators.