Massive galaxies from the early universe found hiding in plain sight

Opened in 2012, the Atacama Large Millimeter/Submillimeter Array (ALMA), shown in figure 1, measures the portion of the spectrum straddling the boundary between radio and IR—a range which is easily absorbed by water in Earth’s atmosphere. The array’s location is ideal. Not only is Chile’s Atacama Desert the driest place on Earth (excluding the poles) but it also has a wide plateau whose 5000 m elevation reduces absorption by water vapor and whose flatness allows the array’s 66 large antennas to be easily moved around and reconfigured. ALMA researchers have published numerous results in the intervening seven years (see, for example, Physics Today, December 2016, page 22). The array is also part of the network of facilities that make up the Event Horizon Telescope, which recently captured the first image of a black hole (see “What it took to capture a black hole,” Physics Today...