Mysterious Decades-Long Radio Signal Discovered in the Milky Way
- A distant Galactic synchrotron transient known as VT J1906+0849 has been spotted by astronomers; it has stayed bright in radio waves for roughly twenty years while displaying a...
- The mysterious source first appeared in data collected in 2017 during the Very Large Array Sky Survey (VLASS), registering around 70 millijanskies as the brightest radio transient discovered...
- Follow-up observations in 2019 and 2024 showed the source growing progressively fainter.
A distant Galactic synchrotron transient known as VT J1906+0849 has been spotted by astronomers; it has stayed bright in radio waves for roughly twenty years while displaying a shifting spectral turnover frequency alongside minimal apparent expansion. The object, located at least 49,000 light-years from Earth beyond the Milky Way’s outer Norma-Cygnus spiral arm, operates on a timescale of decades rather than the milliseconds to months typically observed in changing cosmic sources.
Radio Brightness Measurements across Three Decades
The mysterious source first appeared in data collected in 2017 during the Very Large Array Sky Survey (VLASS), registering around 70 millijanskies as the brightest radio transient discovered by the survey at that distance. Archival checks revealed that nothing was visible at the site in 1996 data from the NRAO VLA Sky Survey. By 2005, the object had begun to change, brightening steadily between 2006 and 2013 to reach a peak of approximately 200 millijanskies in 2014.
Follow-up observations in 2019 and 2024 showed the source growing progressively fainter. However, in late 2025, Very Large Array data captured VT J1906+0849 brightening once again.
Shifting Frequencies
Researchers analyzing the radio spectrum noted that the emission peak shifted erratically over time, moving from approximately 1.9 gigahertz in 2019 down to 0.8 gigahertz in 2024, before climbing back to 2.2 gigahertz in 2026. This behavior defies standard models of expanding synchrotron material, which usually exhibit a predictable frequency drop as a cloud spreads out and cools. Despite these shifts, observations showed little evidence of physical expansion.
Infrared observations revealed evidence of gas moving at approximately 2,000 kilometers per second, consistent with a powerful outflow. Additional studies will be required to ascertain whether VT J1906+0849 actually functions as a younger counterpart to SS 433, or if it represents an even more peculiar phenomenon.
Future Observations and Publication Details
The study, led by Jessie Miller of the California Institute of Technology, has been published in The Astrophysical Journal. Further observations will determine whether VT J1906+0849 represents a younger relative of SS 433 or an entirely different phenomenon.
