Billie Eilish, the 18-year-old phenomenon who swept the Grammys on Sunday, is not a traditional pop star: She whispers nearly as much as she sings, and blurs genres like pop, rock and electronic music. She sports black-green hair, dresses in baggy clothes and collaborates with her older brother.

Music critics say the popularity of her brooding songs and streaming-fueled success signal a shift in pop music away from the radio-friendly stars of the past decade like Taylor Swift and Beyoncé.

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