Free Astronomy Magazine January-February 2016

21 JANUARY-FEBRUARY 2016 the light coming from the white dwarf and its surrounding material over an unprecedented period of twelve years be- tween 2003 and 2015. Observations over periods of years were needed to probe the system from multiple viewpoints. The team identified the unmistakable trident-like spec- tral signature from ionised calcium, call- ed the c a l c i um (Ca II) trip- let. The differ- ence between the observed and known wavelengths of these three lines can determine the velocity of the gas with consider- able precision. “The image we get from the pro- cessed data shows us that these systems are truly disc-like, and re- veals many structures that we can- not detect in a single snapshot,” ex- plained lead author Christopher Man- ser. The team used a technique call- ed Doppler tomography — similar in T his artist’s impression shows how an asteroid torn apart by the strong gravity of a white dwarf has formed a ring of dust particles and debris orbiting the Earth-sized burnt out stellar core SDSS J1228 +1040. Gas produced by collisions within the disc is detected in obser- vations obtained over twelve years with ESO’s Very Large Telescope, and reveal a narrow glowing arc. [Mark Garlick (www.markgarlick.com ) and University of Warwick/ESO] SPACE CHRONICLES