Free Astronomy Magazine January-February 2016

SPACE CHRONICLES principle to medical tomographic scans of the human body — which allowed them to map out in detail the structure of the glowing gaseous remains of the dead star’s meal or- biting J1228+1040 for the first time. While large stars — those more mas- sive than around ten times the mass of the Sun — suffer a spectacularly violent climax as a supernova explo- sion at the ends of their lives, smaller stars are spared such dramatic fates. When stars like the Sun come to the ends of their lives they exhaust their fuel, expand as red giants and later expel their outer layers into space. The hot and very dense core of the former star — a white dwarf — is all that remains. But would the planets, asteroids and other bodies in such a system survive this trial by fire? What would be left? The new observations help to answer these questions. It is rare for white dwarfs to be sur- rounded by orbiting discs of gas- eous material — only seven have ever been found. The team concluded that an aster- oid had strayed dangerously close to the dead star and been ripped apart by the immense tidal forces it experienced to form the disc of ma- terial that is now visible. The orbiting disc was formed in simi- lar ways to the photogenic rings seen around planets closer to home, such as Saturn. However, while J1228+1040 is more than seven times smaller in diameter than the ringed planet, it has a mass over 2500 times greater. The team learned that the distance between the white dwarf and its disc is also quite different — Saturn and its rings could comfortably sit in the gap between them. Although the disc around this white dwarf is much bigger than Saturn’s ring sys- tem in the Solar System, it is tiny com- pared to the debris discs that form planets around young stars. T his plot is an unusual type of image, showing the velocities of the gas in the disc around the white dwarf SDSS J1228+1040, rather than its po- sition. It was mapped out from Very Large Telescope observations over a period of twelve years and by applying a method called Doppler tomogra- phy. The dashed circles correspond to material in circular orbits at two dif- ferent distances from the star. This appears “inside out” because material moves faster in close-in orbits. [University of Warwick/C. Manser/ESO]