This image shows the white dwarf star at the centre of the planetary nebula NGC 6751. White dwarf stars are typically the size of the Earth but with the mass of the Sun and so dense that one teaspoonful would weigh 100 tonnes. They form when a Sun-like star has exhausted its supply of hydrogen fuel, ejects its outer layers and collapses in on itself. The hottest gas in this image is from the Hubble Space Telescope is coloured blue, the coolest red.