Free Astronomy Magazine July-August 2016

SPACE CHRONICLES raining in on the supermassive black hole at the centre of a huge galaxy one billion light-years from Earth. The results appeared in the journal Nature on 9 June 2016. The new AL- MA observation is the first direct evi- dence that cold dense clouds can coalesce out of hot intergalactic gas and plunge into the heart of a gal- axy to feed its central supermassive black hole. It also reshapes astron- omers’ views on how supermassive black holes feed, in a process known as accretion. Previously, astronomers believed that, in the largest galaxies, super- massive black holes fed on a slow and steady diet of hot ionised gas from the galaxy’s halo. The new ALMA observations show that, when the in- tergalactic weather conditions are right, black holes can also gorge on a clumpy, chaotic downpour of giant clouds of very cold molecular gas. “Although it has been a major theoretical prediction in recent years, this is one of the first unambiguous pieces of observation- al evidence for a cha- otic, cold rain feeding a supermassive black hole,” said Grant Tremblay, an astrono- mer with Yale Univer- sity in New Haven, Connecticut, USA, for- mer ESO Fellow, and lead author on the new paper. “It’s ex- citing to think we might actually be ob- serving this galaxy- spanning rainstorm feeding a black hole whose mass is about 300 million times that Black hole fed by cold intergalactic deluge A n international team of as- tronomers using the Ata- cama Large Millimeter/sub- millimeter Array (ALMA) has witnes- sed a cosmic weather event that has never been seen before — a cluster of towering intergalactic gas clouds by ALMA Observatory D eep in the heart of the Abell 2597 Brightest Cluster Galaxy, astronomers see a small cluster of giant gas clouds raining in on the central black hole. They were revealed by the billion light-year-long shadows they cast toward Earth. These ALMA data present the first observa- tional evidence for predicted chaotic cold accretion onto a supermassive black hole. [NRAO/AUI/NSF; Dana Berry/SkyWorks; ALMA (ESO/NAOJ/NRAO)]