Free Astronomy Magazine May-June 2019

54 MAY-JUNE 2019 SPACE CHRONICLES by ALMA Observatory Astronomers study mysterious new type of cosmic blast W hen astronomers discov- ered a cosmic explosion in a galaxy nearly 200 million light-years from Earth last June 16, they soon realized it was something different. While still debating the details, scientists now believe they may have gotten their first glimpse of the birth of a powerful phenome- non seen throughout the Universe. The explosion was discovered by the ATLAS all-sky survey system in Hawaii, and immediately got the attention of astronomers. First, it was unusually bright for a supernova explosion — a common source of such outbursts. In addition, it brightened, then faded, much faster than expected. Half a year later, “despite being one of the most intensely studied cosmic events in history, watched by as- tronomers all over the world, we still don’t knowwhat it is,” said Anna Ho, of Caltech, who led a team using the Atacama Large Millimeter/submilli- meter Array (ALMA), in Chile, among other telescopes. The object, dubbed AT2018cow, “heralds a new class of energetic cosmic blasts,” Ho added. The explosion’s unusual characteris- tics “were enough to get everybody excited,” said Raffaella Margutti, of Northwestern University, who led a A rtist’s con- ception of a cos- mic blast with a “central engine,” such as that suggested for AT2018cow. Black hole at center is pulling in material that forms a rapidly-rotating disk that radiates prolific amounts of energy and propels superfast jets of material from its poles. Jet encounters material surrounding the blast. [Bill Saxton, NRAO/AUI/NSF]