X-rays that don't come from any known source

Space is filled with types of light we can’t see — from infrared signals released by hot stars and galaxies, to the cosmic microwave background. Some of this invisible light that fills space takes the form of X-rays, the source of which has been hotly contended over the past few decades. A new study confirms some ideas about where these X-rays come from, shedding light on our solar neighborhood’s early history. But it also reveals a new mystery — an entire group of X-rays that don’t come from any known source.

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