Free Astronomy Magazine July-August 2015

SPACE CHRONICLES a bright and eerie goblin-green hue. They offer new insights into the tur- bulent pasts of these galaxies. The ethereal wisps in these images were illuminated, perhaps briefly, by a blast of radiation from a quasar — a very luminous and compact region that surrounds a supermassive black hole at the centre of a galaxy. Galac- tic material falls inwards towards the central black hole, growing hot- ter and hotter, forming a bright and brilliant quasar with powerful jets of particles and energy beaming above and below the disc of infal- ling matter. In each of these eight images a qua- sar beam has caused once-invisible filaments in deep space to glow through a process called photoioni- sation. Oxygen, helium, nitrogen, sulphur and neon in the filaments Hubble finds ghosts of quasars past by NASA T he NASA/ESA Hubble Space Telescope has imaged a set of enigmatic quasar ghosts — ethereal green objects which mark the graves of these objects that flickered to life and then faded. The eight unusual looped structures orbit their host galaxies and glow in T his image shows the winding green filaments observed by the NASA/ESA Hubble Space Telescope within eight different galaxies. The ethereal wisps in these images were illuminated, perhaps briefly, by a blast of radiation from a quasar — a very luminous and compact region that surrounds a supermassive black hole at the centre of a galaxy. In each of these eight images a quasar beam has caused once-invisible filaments in deep space to glow through a process called photoionisation. Oxygen, helium, nitrogen, sulphur and neon in the filaments absorb light from the quasar and slowly re-emit it over many thousands of years. Their unmistakable emerald hue is caused by ionised oxygen, which glows green. [NASA, ESA, Galaxy Zoo Team and W. Keel (University of Alabama, USA)]