This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Astronomers have identified a peculiar radio transient in the Milky Way that has remained active for more than two decades, defying the behavior expected of known classes of galactic radio sources. The paper posted to the arXiv preprint server on Aug. 21 discusses the rare event that may have caused this bizarre radio emission.
Transient radio emission—radio waves from astronomical sources that brighten, fade or change over time—arises from a number of violent cosmic events. These include rapidly spinning neutron stars, shocks produced when powerful stellar winds interact with their surroundings, and mass accretion by white dwarfs from their companion stars in binary systems, among others. Extragalactic radio transients, particularly fast radio bursts, have been discovered in large numbers in recent years.
Within the Milky Way, however, the population of radio transients remains much less explored. While searching for such sources at low galactic latitudes, astronomers discovered VT J1906+0849, the brightest known transient in the Very Large Array Sky Survey (VLASS). Its first detection with VLASS was recorded on Oct. 27, 2017.
The team, led by Jessie M. Miller of the California Institute of Technology, carried out a multiwavelength investigation of VT J1906+0849 to determine what this unusual radio transient actually is. They combined archival observations with new follow-up observations across radio, infrared, optical and X-ray wavelengths.
Researchers estimated that it had brightened by at least a factor of six over roughly 21 years. Archival data revealed an earlier detection in 2005 by the MAGPIS survey, when it was about 35 millijansky (mJy) at 4.86 gigahertz, while its brightness appears to have peaked at more than 200 mJy around 2014. It subsequently faded before undergoing a new rebrightening in late 2025.
Very Long Baseline Array observations from 2010, 2022 and new observations in 2025 showed that the emitting region is extremely compact. The team estimated the source's distance to be in the range of 15 kpc (49,000 light-years) to 32 kpc (104,000 light-years). A Swift X-ray observation detected no X-ray counterpart.
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