Astronomers have discovered a strange radio source within the Milky Way galaxy that has remained active for more than two decades, in a rare case that combines a continuous change in radiation intensity with the absence of any clear X-ray counterpart.
The source is named "VT J1906+0849", and following up on old observational records along with radio, optical, infrared and X-ray telescopes has allowed for the reconstruction of its story over more than 20 years.
The significance of the discovery lies in the fact that it may reveal an unknown type or rare stage in the life of compact objects, such as black holes or neutron stars.
The story truly began when the source appeared in the Very Large Sky Survey (VLASS) radio telescope on October 27, 2017, with a brightness of about 70 millijanski. But researchers, led by Jesse Miller of the California Institute of Technology, went back through older archives and found a detection of the source dating back to 2005.
The data showed that it increased in brightness until it exceeded 200 milliseconds in 2014, then its brightness decreased before it began to glow again in late 2025. Thus, scientists were not faced with a short-lived explosion, but rather a source that changes slowly over decades.
Bright on the radio, absent in the X-ray
Observations reveal that the region emitting radiation is extremely small, and, remarkably, has shown little expansion despite years of activity. Measurements taken by the Very Large Telescope (VLT) network in 2010, 2022, and 2025 showed that the emitting region remained compact, while its spectrum and brightness changed significantly.
Scientists estimate that the source is located at least 15 kiloparsecs, or about 50,000 light-years, and possibly much farther.
Then came another surprise: the Swift space observatory detected no X-ray equivalent of the source. This finding is significant because the estimated high temperature of the radio region, ranging from 100 million to 10 billion Kelvin, suggests that the radiation is not ordinary thermal radiation, but rather likely produced by high-energy particles moving within a strong magnetic field and emitting radiation known as synchrotron radiation.
This made the question more complicated: What object could produce such a powerful radio for so many years, while appearing almost invisible in X-rays?
A black hole or a neutron star behind a thick veil?
The team considered several possibilities, including supernovae, binary star systems, novae, and various types of neutron stars, but the source's characteristics didn't readily fit any of them. Therefore, the researchers lean toward a scenario in which a compact object, perhaps a black hole or a neutron star, constantly feeds on surrounding matter, emitting jets of particles and magnetic fields that produce radio emissions.
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