Free Astronomy Magazine September-October 2015

are bursting with dramatic knots of star formation and intensely bright central regions. Within this single group, astrono- mers have found two LINERs, one Seyfert 2 galaxy and three starburst galaxies. These three types of galaxy are all quite different, and can each help us to explore something diffe- rent about the cosmos. Starbursts are dynamic galaxies that produce new stars at much greater rates than their peers. LI- NERs (Low-Ionisation Nuclear Emission-line Regions) contain heat- ed gas at their cores, which spew out radia- tion. In this image NGC 839 is a LINER-type and luminous infrared galaxy and its compan- ion NGC 838 is a LINER- type galaxy with lots of starburst activity and no central black hole. The remaining galax- ies, NGC 835 and NGC 833, are both Seyfert 2 galaxies which have in- credibly luminous cores when observed at other wave- lengths than in the visible light, and are home to active supermassive black holes. The X-ray emission ema- nating from the black hole within NGC 833 (far right) is so high that it suggests the galaxy has been strip- ped of gas and dust by past interac- tions with other galaxies. It is not alone in having a violent history — the morphology of NGC 839 (far left) is likely due to a galactic merger in the recent past, and long tails of glowing gas can be seen stretching away from the galaxies on the right of the image. This new image uses observations from Hubble's Wide Field Planetary Camera 2, combined with data from the ESO Multi-Mode Instrument in- stalled on the European Southern Observatory’s New Technology Tele- scope in Chile. A version of this image was entered into the Hubble's Hid- den Treasures image processing com- petition by contestants Jean-Chris- tophe Lambry and Marc Canale. n T his video zooms in from a view of the night sky, through the constellation of Cetus (The Sea Monster), to end on new NASA/ESA Hubble Space Telescope observations of galaxy group HCG 16. The final image uses observations from Hubble’s Wide Field Planetary Camera 2, com- bined with data from the ESO Multi-Mode In- strument installed on the European Southern Observatory’s New Technology Telescope in Chile. [NASA, ESA, Digitized Sky Survey 2. ESO]