10, 2010, the European Space Agency's INTEGRAL satellite detected a transient X-ray source
in the direction of Terzan 5, a globular star cluster about 25,000 light-years away toward the constellation Sagittarius.
They comprise low-resolution X-ray spectral instruments, a binocular Ritchey-Chretien telescope, and a detector with a huge 10[degrees]-by-90[degrees] field of view that will scan the sky for transient X-ray sources
Draine and Woods say transient X-ray sources
could provide the radiation necessary to heat and ionize gas, thereby exciting hydrogen atoms, which would then emit the ultraviolet light.