* Dark galaxies are small, gas-rich galaxies in the early Universe that are very inefficient at forming stars, predicted by theories of galaxy formation, and are thought to be the building blocks of today’s bright, star-filled galaxies. Astronomers think that they may have fed large galaxies with much of the gas that later formed into the stars that exist today. Because they are essentially devoid of stars, these dark galaxies don’t emit much light, making them very hard to detect.

* “Our approach to the problem of detecting a dark galaxy was simply to shine a bright light on it.” explains Simon Lilly of ETH Zurich, Switzerland. “We searched for the fluorescent glow of the gas in dark galaxies when they are illuminated by the ultraviolet light from a nearby and very bright quasar. The light from the quasar makes the dark galaxies light up in a process similar to how white clothes are illuminated by ultraviolet lamps in a night club.” (Quasars are very bright, distant galaxies that are believed to be powered by supermassive black holes at their centres.)

* The team took advantage of the large collecting area and sensitivity of the Very Large Telescope (VLT), and a series of very long exposures, to detect the extremely faint fluorescent glow of the dark galaxies. They used the FORS2 instrument to map a region of the sky around the bright quasar HE 0109-3518, looking for the ultraviolet light that is emitted by hydrogen gas when it is subjected to intense radiation. Because of the expansion of the Universe, this light is actually observed as a shade of violet by the time it reaches the VLT.

http://www.dailygalaxy.com/my_weblog/2012/07/dark-galaxies-of-the-universe-observed-for-the-first-time.html

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“Bullet-Shooting Black Hole”: “Black holes are known for sucking in matter, but researchers find they can shoot it out as well.  Observations of a black hole called H1743-322, which harbors five to 10 times the mass of the sun and is located about 28,000 light-years from Earth, revealed it apparently pulled matter off a companion star, then spat some of it back out as gigantic “bullets” of gas moving at nearly a quarter the speed of light.  The black hole’s “belch” is actually a bipolar jet of plasma (ionized gas) that discharges particles from the centre of an accretion disc (a structure that moves material toward its centre - in this case, the black hole).  This galactic belch ejects particles, scattering them amongst stars and planets, and may also affect magnetic fields in the galaxy.” Credit: Greg Sivakoff/University of Alberta.