Free Astronomy Magazine July-August 2016

SPACE CHRONICLES Very Long Baseline Array indicate that the gas clouds observed by ALMA are only about 300 light- years from the central black hole, essentially teetering on the edge of being devoured, in astronomical terms. While ALMA was only able to detect three clouds of cold gas near the black hole, the astronomers spec- ulate that there may be thousands like them in the vicinity, setting up the black hole for a continuing downpour that could fuel its activity for a long time. The astron- omers now plan to use ALMA to search for these "rainstorms" in other galaxies in or- der to determine whether such cosmic weather is as common as current theory sug- gests it might be. T he background image (blue) is from the NASA/ESA Hubble Space Telescope. The foreground (red) is ALMA data showing the distribution of carbon monoxide gas in and around the galaxy. The pull-out box shows the ALMA data of the "shadow" (black) produced by absorption of the milli- metre-wavelength light emitted by electrons whiz- zing around powerful mag- netic fields generated by the galaxy's supermassive black hole. The shadow indicates that cold clouds of molecu- lar gas are raining in on the black hole. [B. Saxton (NRAO/AUI/NSF)/G. Trem- blay et al./NASA/ESA Hub- ble/ALMA (ESO/NAOJ/NRAO)] Suns and is tens of light-years across. Normally, objects on that scale would be diffi- cult to distin- guish at these cosmic distances, even with AL- MA’s amazing resolution. They were revealed, however, by the billion-light-year- long “shadows” they cast toward Earth. The shad- ows are formed when the in-fal- ling opaque gas clouds block out a portion of the bright background millimetre-wave- length light emitted by electrons spiraIling around magnetic fields very near the central supermassive black hole. Additional data from the National Science Foundation’s T he cosmic weather report, as illustrated in this artist’s concept video, calls for condensing clouds of cold mole- cular gas around the Abell 2597 Brightest Cluster Galaxy. The clouds condense out of the hot, ionised gas that suffuses the space between the galaxies in this cluster. New ALMA data show that these clouds are raining in on the galaxy, plunging toward the supermassive black hole at its centre. [NRAO/AUI/ NSF; Dana Berry/SkyWorks; ALMA (ESO/NAOJ/NRAO)] of the Sun.” Tremblay and his team used ALMA to peer into an un- usually bright cluster of about 50 galaxies, collectively known as Abell 2597. At its core is a massive ellipti- cal galaxy, descriptively named the Abell 2597 Brightest Cluster Galaxy. Suffusing the space between these galaxies is a diffuse atmosphere of hot ionised gas, which was previous- ly observed with NASA’s Chandra X- ray Observatory. "This very, very hot gas can quickly cool, condense, and precipitate in much the same way that warm, humid air in Earth's atmosphere can spawn rain clouds and precipita- tion," Tremblay said. "The newly condensed clouds then rain in on the galaxy, fueling star formation and feeding its supermassive black hole." Near the centre of this gal- axy the researchers discovered just this scenario: three massive clumps of cold gas are careening toward the supermassive black hole in the galaxy’s core at about a million ki- lometres per hour. Each cloud con- tains as much material as a million n