Multimessenger astronomy probes deep-space events with an arsenal of lenses

On September 22, 2017, four billion years into its journey through space, a ghostly particle hit the ice under Earth’s South Pole. This rare event was picked up by IceCube, the largest neutrino detector on the planet, triggering a worldwide alert. In response, telescopes on the ground and in orbit turned toward the region of the sky that had produced the particle to collect other particles and waves coming from the same source. These diverse tools allowed physicists to work out where this cosmic messenger came from—and the answer took everyone by surprise (1).In July 2018, using measurements from Fermi, VERITAS in southern Arizona (pictured), and other telescopes, researchers revealed for the first time the origins of a high-energy neutrino, tracing it to a supermassive black hole at the center of a distant galaxy. Image credit: NSF/VERITAS.It was a shining example of multimessenger astronomy (MMA)—the use of different types of cosmic “messengers” to study deep-space phenomena. Those messengers include electromagnetic waves (i.e., light, radio, and others), particles (e.g., neutrinos and cosmic rays), and the ripples in spacetime called gravitational waves. MMA builds on multiwavelength studies, which began in the mid-20th century and combine observations of different swaths of the electromagnetic spectrum. The idea driving MMA is to merge the strengths of individual tools, offering a synergistic approach.MMA also brings together researchers who approach astronomy in different ways, says astrophysicist Teddy Cheung at the Naval Research Laboratory in Washington, DC, who has searched for the sources of neutrinos, such as those in the 2017 event, using gamma ray data collected by the Fermi orbiting telescope. “Every type of researcher, including theorists, experimentalists, and observers is really excited about talking to each other,” he says. MMA is now helping astronomers test theories about deep space events, make serendipitous …