The Milky Way's Radio Ghost Refuses to Expand
A radio source appeared after decades of silence, brightened, faded and returned. Its suspected outflow races at about 2,000 kilometres per second while the source itself barely grows.
Twenty-One Years From Nothing to Loud
When astronomers compared two major radio surveys, one point in the Milky Way had changed completely. It was absent from the NRAO VLA Sky Survey, then appeared 21 years later in the Very Large Array Sky Survey as a 70-millijansky source.
The object, VT J1906+0849, was not a brief flash. Archival observations in a new 50-page preprint show that it was first detected in 2005, climbed above 200 millijanskys around 2014, faded, and then brightened again late in 2025.
This transient has spent two decades refusing to behave like one.
The Missing X-Rays
Its position close to the Galactic plane and its infrared counterpart both favour a home inside the Milky Way. At a likely distance of at least 15,000 parsecs, the radio luminosity points toward sustained feeding of a compact object — a neutron star or black hole drawing matter from a companion.
That explanation immediately hits a problem. Swift detected no X-ray counterpart bright enough to match ordinary Galactic X-ray binaries. The source's long radio evolution and changing spectrum also differ from the familiar flare-and-fade pattern.
- Radio spectra are consistent with synchrotron self-absorption.
- Very long baseline measurements show little or no expansion over more than five years.
- Infrared spectra contain a broad, variable line interpreted as hydrogen moving in an asymmetric outflow near 2,000 kilometres per second.
The radio-emitting region changes internally without visibly inflating as an ordinary blast wave should.
A Jet Inside a Wind
The team proposes one possible model: a young relative of the strange microquasar SS 433. In that picture, a dense wind from the feeding disk traps or confines a continuously powered synchrotron jet. The collision keeps the radio source compact and may help hide the X-rays.
That remains an interpretation, not a classification. The study is a preprint and VT J1906+0849 has not yet been placed securely inside any known family of stellar remnants or binaries. Continued radio, infrared and X-ray monitoring can test whether the outflow geometry and rebrightening repeat.
Some cosmic explosions announce themselves by expanding. This one may be loud because something will not let it escape.