What Astronomers are Gleaning from a Big Blast Called “Cow”

Caltech News tagged with “astronomy + exoplanets + JPL + planetary_science”

On June 16, 2018, a brilliant stellar explosion unlike any seen before went off in the skies, quickly capturing the attention of astronomers around the globe. First spotted by the ATLAS survey in Hawaii, the event was dubbed AT2018cow through a randomized naming system, and soon earned the nickname “Cow.” Just three days after exploding, Cow had become 10 times brighter than a typical supernova—a powerful explosion that heralds the death of a massive star.”We still don’t know what this is, although it is one of the most intensely studied cosmic events in history,” says Anna Ho (MS ’17), a graduate student at Caltech and lead author of a new study about the event. Cow was likely a supernova, she says, although some scientists have proposed that it instead may have been caused by a black hole ripping apart a type of star called a white dwarf. In the hours, days, and weeks after the event, telescopes on the ground and in space set their sights on Cow, witnessing a dramatic increase in brightness across the electromagnetic spectrum, from high-energy X-rays to low-energy radio waves. Ho and her colleagues observed millimeter-wave light, which is slightly higher in energy than radio waves. “We’ve never seen a supernova this bright in millimeter waves,” she says. “We were shocked.” Ho presented these results on January 10 at the 233rd meeting of the American Astronomical Society in Seattle. She and her team began observing Cow five days after it exploded using the Submillimeter Array in Hawaii, and soon after using the National Science Foundation-funded Atacama Large Millimeter Array (ALMA) in Chile. They observed the event, which has since declined in brightness in millimeter waves, on and off for a total of 80 days.Ho says that the millimeter-wave data reveal that a shock wave is traveling outward from the explosion at one-tenth the speed of light. ” …

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