Astronomers Catch Black Holes “Burping” in Radio with the NSF VLA

Credit: NSF/AUI/NSF NRAO/B.Foott

Astronomers using the U.S. National Science Foundation Very Large Array (NSF VLA) have found that when a supermassive black hole tears apart an unlucky star, the fireworks are not over when the first flash fades. Years after the initial outburst, many of these black holes "burp" out streams of material that slam into surrounding gas and glow in radio waves, giving the NSF VLA a front-row seat to how black holes grow and blast energy back into their galaxies.

When a star wanders too close to a supermassive black hole, the black hole's gravity shreds it in a tidal disruption event, or TDE, producing a bright flash of optical, ultraviolet, and X-ray light from the center of an otherwise quiet galaxy. Once that flare fades, the black hole sinks back into obscurity.

At radio wavelengths, however, the story is just getting started. Follow-up observations with the NSF VLA have revealed that long after the visible light has dimmed, a surprising number of these stellar destruction events produce a delayed radio flare that can brighten months to years later. It is as if the black hole, having devoured most of the star, lets out a powerful "burp" that the NSF VLA can pick up from billions of light-years away. "We used to think the show was over once the optical light faded," said lead author Kate Alexander of the University of Arizona. "In fact, our first large program dedicated to systematically studying TDEs with the NSF VLA focused on the first year after discovery, and we were surprised to find that many TDEs don't show radio light during this time frame at all. Fortunately we kept looking, and now the NSF VLA is showing us that the black hole can come back years later with a dramatic encore performance in radio light."

In the new study, the team used the NSF VLA as the workhorse for late-time radio observations of 31 tidal disruption events. Professor Yvette Cendes of the University of Oregon played a key role in analyzing much of the radio data; a companion study (Cendes et al. 2024) models the radio light in depth and provides an important foundation for the results reported here. In the new study, when combined with optical, ultraviolet, and X-ray data from other facilities, the NSF VLA measurements allowed the team to track when and how strongly each system lit up in radio, and to connect those "burps" to what the black hole was doing at the time.

Tidal disruption events offer a rare chance to watch a supermassive black hole's feeding rate change in real time. At first, the black hole swallows stellar debris very quickly; over time, as the supply of gas dwindles, the feeding slows down. By catching these systems repeatedly with the NSF VLA, astronomers can see how the radio emission responds as the black hole's meal progresses. In this work, the team combined detailed modeling of the optical and ultraviolet light curves with measurements of the radio and X-ray brightness. That let them estimate how fast each black hole was accreting gas when the NSF VLA detected a delayed radio flare. They found that late-time radio emission does not arise from a single "just right" feeding state, but from two distinct scenarios. In some galaxies, the NSF VLA detects radio emission turning on hundreds of days after a tidal disruption event (TDE), while the black hole is still rapidly accreting. In others, the flare appears only after the system has quieted and accretion has slowed significantly. In both cases, part of the infalling gas is expelled outward rather than fully consumed.

The NSF VLA data indicate that this delayed radio emission is produced when outflowing material from near the black hole collides with surrounding gas, generating shock waves that accelerate particles and produce radio waves. These "burps" serve as direct evidence of jets or winds launched close to the event horizon. This behavior mirrors that seen in other black hole systems, where both very high and very low accretion rates can drive radio-bright outflows. By linking the timing and strength of these signals to the black hole's feeding state, the observations provide strong evidence that TDEs follow the same underlying physics. The results also suggest that black holes can continue accreting disrupted stellar material longer than expected, with some radio flares occurring during prolonged high accretion and others emerging after the rate has dropped to a trickle.

The work also offers a practical roadmap for making the most of the NSF VLA in future tidal disruption events. The team finds that TDEs which later produce delayed radio emission are less likely to show helium emission lines in their early optical spectra. Those events, which appear different in visible light from the start, may be the best candidates for long-term monitoring with the NSF VLA to catch future "burps." By assembling the largest sample of tidal disruption events yet studied at radio wavelengths and using the NSF VLA to follow them over years, this work shows that these events are not one-off anomalies. They are ongoing stories in which supermassive black holes feed, launch outflows, and reshape their surroundings. The VLA's sensitive radio vision makes it possible to listen in on those delayed, cosmic belches, and to use them to understand how black holes and galaxies grow together.

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This news is featured in a press conference at the American Astronomical Society's 248th meeting on Monday, June 15th at 2:15pm PDT. Find a recording from this presentation on the AAS Press Office YouTube channel.

This news article was originally published on the NRAO website on June 15, 2026.