[In The Music of the Spheres, Guy Murchie] describes the surprising lack of density in certain stars, even when those stars, nonetheless, seem structurally coherent to an outside observer.
He explains, for instance, that the surface of the sun "is really a thousand times more vacuous than a candle-flame on Earth, and even the concentrated moiling gases hidden a thousand miles below it are a hundred times thinner than earthly air." In fact, other stars—such as E Aurigae I, so huge it could "contain most of our solar system, including the 5.5-billion-mile circumference of Saturn's orbit"—are often "described as 'red-hot vacuums,'" Murchie writes, "because their material, though hot, averages thousands of times thinner than earthly air and is normally invisible, so that you might fly through them for days in your insulated space ship without even realizing you were inside a star."