Black holes are drains in space that have gravitational pull so strong that nothing, not even light, can escape. Huge ones are believed to lurk at the centres of many galaxies including the Milky Way, which contains the sun. The one-way journey from the heart of a galaxy into the oblivion of a black hole probably takes about 200,000 years, astronomers said. By tracking the death spiral of cosmic gas at the centre of a galaxy called NGC1097, scientists figured that material moving at 177,000 km an hour would still take eons to cross into a black hole.