A mysterious gamma-ray glow that suffuses our galaxy has been tracked down to a set of distinct sources – many of them black holes.



The new work settles a 30-year-old debate about…


where “soft”, or relatively low energy, gamma rays come from and lays to rest convoluted theories devised to account for the radiation.



“There was a profound mystery in gamma-ray astronomy about what was seen from our own galaxy … now the mystery is solved,” says Neil Gehrels, at NASA’s Goddard Space Flight Center.



Gamma rays are absorbed by the Earth’s atmosphere, so the first measurements were not made until high-altitude balloon flights in the late 1960s. These showed the Milky Way was awash with gamma-rays, but their origin could not be pinned down accurately.



In the early 1990s, a French space telescope named SIGMA found about 10 discrete…



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