“An object flung upwards from the surface of the Earth must have a speed in excess of 11 kilometres per second to escape into deep space. This is known as Earth’s escape velocity. The gravitational pull at the Sun’s surface is much stronger, and the escape velocity is correspondingly higher at 620 kilometres per second. At the surface of a neutron star, the escape velocity can approach an appreciable fraction of the speed of light.‡ Laplace calculated that a body with a density comparable to the Earth but with a diameter 250 times larger than the Sun would have a gravitational pull so great that the escape velocity would exceed the speed of light, and therefore ‘the largest bodies in the Universe may thus be invisible by reason of their magnitude’.3”