A Tour of NGC 6388

Narrator (April Hobart, CXC): The destruction of a planet may sound like the stuff of science fiction, but a team of astronomers has found evidence that this may have happened in an ancient cluster of stars at the edge of the Milky Way galaxy. Using several telescopes, including NASA's Chandra X-ray Observatory, researchers have found evidence that a white dwarf star - the dense core of a star like the Sun that has run out of nuclear fuel - may have ripped apart a planet as it came too close.

How could a white dwarf star, which is only about the size of the Earth, be responsible for such an extreme act? The answer is gravity. When a star reaches its white dwarf stage, nearly all of the material from the star is packed inside a radius one hundredth that of the original star. This means that, for close encounters, the gravitational pull of the star and the tides associated with it are greatly enhanced. For example, the gravity at the surface of a white dwarf is over ten thousand times higher than the gravity at the surface of the Sun.

Chandra's excellent X-ray vision enabled the astronomers to determine that the X-rays from NGC 6388 were not coming from a black hole at the center of the cluster, but instead from a location slightly off to one side. This ruled out a central black hole as the source of the X-rays, so the hunt for clues about the nature of the X-rays in NGC 6388 continued. Monitoring NGC 6388 with the Swift telescope, astronomers watched as the source become dimmer over 200 days. The rate at which the X-ray brightness dropped matched theoretical models for the disruption of a planet by the gravitational tidal forces of a white dwarf. Astronomers will continue to study NGC 6388 in order to learn everything they can about this interesting object on the outskirts of our Milky Way galaxy.