Scientists Solve Mystery of Why Black Holes Burp Radio Jets

Astronomers tracking supermassive black holes have discovered that delayed radio emissions, often described as cosmic “burps,” occur when these massive entities feed either too rapidly or too slowly, according to research presented at the 248th meeting of the American Astronomical Society.

Supermassive black holes are notoriously messy when devouring nearby stars, a catastrophic process known as a Tidal Disruption Event, or TDE, where intense gravitational fields shred an unlucky star into a spaghetti-like stream of gas debris. While visible light from these events eventually dims, research led by the University of Arizona’s Kate Alexander shows that roughly 40% of all TDEs let out massive radio flares months or even years after the initial cosmic feast appears finished.

Unraveling Tidal Disruption Event Radio Flares

For years, targeted radio follow-up of stellar disruptions typically ceased if no emission was detected within the first year, leaving long-term behavior largely unstudied, according to Alexander. Over the past six years, astronomers utilized the Karl G. Jansky Very Large Array telescope in New Mexico to conduct large-scale, systematic radio observations of several dozen nearby TDEs. A 2024 paper co-authored by Alexander and University of Oregon radio astronomer Yvette Cendes first established that roughly 40% of TDEs produce delayed radio detections.

To uncover why these dormant systems reactivate, Alexander’s team analyzed 91 TDE candidates discovered between 1990 and 2019, narrowing their focus to a gold-standard sample of 31 events with comprehensive multiwavelength tracking. By blending VLA radio data with archival optical and ultraviolet observations alongside fresh X-ray measurements, the researchers mapped the precise volume of gas consumed by the black holes over time. Matching those feeding timelines against the exact emergence of radio flares revealed the underlying mechanics of the outflows.

Dietary Phases and Cosmic Indigestion

The data demonstrated that delayed radio flares ignite at two opposite extremes. According to the findings presented in California, these outbursts occur either while a black hole is rapidly overgorging on gas or after its feeding rate has slowed to a crawl.

Sometimes, after it seems like they are done eating, they may get indigestion and they may let out a large radio ‘burp,’

Kate Alexander, University of Arizona

In both scenarios, a fraction of the incoming gas is flung outward rather than being fully consumed. This expelled material slams into the gas surrounding the black hole, triggering particle-accelerating shock waves that produce detectable radio emissions. Alexander noted that this cosmic feeding mechanic operates identically across all scales, functioning the exact same way regardless of whether the black hole is a relative lightweight or a behemoth millions of times more massive than the sun.