Sean Waite, the agent in charge for the DEA in Albuquerque, said he could not comment on the Rivers case because it is ongoing. He disputed allegations that Rivers was targeted because of his race. Waite said that in general DEA agents look for "indicators" such as whether the person bought an expensive one-way ticket with cash, if the person is traveling from or to a city known as a hot spot for drug activity, if the person's story has inconsistencies or if the large sums of money found could have been transported by more conventional means.

"We don't have to prove that the person is guilty," Waite said. "It's that the money is presumed to be guilty."

In and of themselves, X-rays from the galactic center aren't unusual. But the X-rays NuSTAR detects don't seem to be associated with structures already known to exist. For example, a supernova remnant named Sgr A East emits low-energy X-rays but not high-energy X-rays. The high-energy blotch doesn't correlate with structures seen in radio images either, such as the dust and gas clouds of Sgr A West that are falling toward the supermassive black hole.

Instead, Perez and her colleagues propose that thousands of stellar corpses could be responsible for the high-energy X-rays: massive (and still-growing) white dwarfs, spun-up pulsars, or black holes or neutrons stars feeding on low-mass companion stars.