Atoms find quantum solace in the deep chill of space: But at ultracold temperatures, the particles are more sluggish, allowing the electron to, in effect, have one foot on its own calcium atom and another on the ytterbium ion. As quantum objects, the particles behave like waves, and they remain close to each other long enough for their wavelengths to overlap. This is essentially equivalent to being a single molecule in an excited, or less stable, energy state. If the quasi-joined particles then emit a photon, they can relax into a lower energy state, becoming a bona fide molecule in a process known as radiative association. "These radiative processes are much more likely at low temperature," Hudson says. "It's because of them that we see this enormous reaction rate."
That's exciting to astrochemists like Jean Turner, also of UCLA. "Radiative association is a key starting point of interstellar chemistry," she says.