In the dense stellar arm of our Galaxy, telescopes have spotted a point that emits gamma rays — the most energetic radiation in the Universe. For a long time, no one could say what this object was. It didn't blink, didn't move, and no star or gas cloud was visible nearby. Such 'silent' sources are a real headache: there are hundreds of them in catalogs, but only a few have known natures.

Now, the mysterious point named HESS J1832-085 has a possible explanation. Scientists took 17 years of data from the Fermi space observatory and found a faint but confident gamma-ray signal at the same location, at slightly lower energies. In old X-ray images, they also found a dim source, like a smoldering ember next to a bright fire. Together, it all fits a picture familiar to astronomers: this is how a gamma-ray binary shines.

A gamma-ray binary is a pair of stars, one of which is dead. What remains is a pulsar — an ultra-dense sphere the size of a city, spinning dozens of times per second and emitting streams of particles like a garden sprinkler. These particles slam into the companion star or its wind, and the impact produces gamma-ray emission. It brightens and fades as the pulsar's orbit takes it in and out of the dense stellar wind.

So far, no periodicity has been caught for HESS J1832-085: the orbit might be highly elongated, or we might be viewing it from an unfavorable angle. But all other signs are in place. If future observations confirm the hypothesis, the list of rare gamma-ray binaries will gain another member, and that will help us understand how the most powerful particle accelerators in the Galaxy work.