The transitory nature of a spiral structure at that epoch could explain why Law and his colleagues found just one spiral in their galactic survey. In fact, BX 442 may have evolved into a different shape in the billions of years since it emitted the light now reaching Earth. "It's impossible to say what happened to that spiral galaxy," Conselice says. "It's not like the galaxy types are set in stone."
BX 442 could also have generated its own spiral structure without a nudge from its neighbor, Elmegreen notes. Clumps of stars and gas within a galaxy can cause spirals to form, and BX 442 appears to contain at least one large clump along one of its spiral arms. "They perturb everything around them, and each clump sort of makes its own tidal tail," Elmegreen says. "That's a rather easy way to get three spiral arms, and this galaxy has three arms."
It may be that numerous different mechanisms can shape a spiral galaxy. Many more examples should be accessible for study once next-generation observatories, such as NASA's James Webb Space Telescope, come online. Until then, astronomers will have to rely on unique specimens such as BX 442 to help clear up which are the dominant forces creating spiral structure at different times in the universe's history. "We don't really have a good explanation for how the spiral arms exist," Conselice says. "There's a lot of questions that we just haven't answered."