Astronomers have solved a long-standing cosmic mystery by discovering that supermassive black holes unleash delayed radio “burps” during two distinct phases of their stellar feeding cycle. Published in Nature Astronomy and The Astrophysical Journal, the new research reveals how feeding rates dictate when massive jets are launched into space.
Tracking the Long-Term Echoes of Tidal Disruption Events
Supermassive black holes are notoriously messy when devouring a star, but they can linger over their meals, letting out massive radio burps months or even years after their cosmic feast appears finished. When an unlucky star wanders too close to a supermassive black hole, intense gravitational fields shred it into a spaghetti-like stream of gas debris in a process known as spaghettification. As Dr Adelle Goodwin, an astrophysicist at Curtin University in Western Australia, noted, You have to get really, really close to a black hole to get to the event horizon,
adding that Stars get destroyed further out than that.
Goodwin, also a Forrest Research Foundation fellow, explained that only about half of the star that gets too close to the black hole ends up being swallowed, while the rest is launched back into space in powerful jets and outflows that can influence an entire galaxy’s evolution.
Historically, targeted radio follow-up of these tidal disruption events ceased if no emission was detected within the first year or so, leaving their long-term behavior unstudied. Over the past six years, astronomers have been using the Karl G. Jansky Very Large Array telescope in New Mexico to conduct the first large-scale, systematic radio observations of several dozen nearby events.
Two Distinct Phases of Cosmic Indigestion
Working independently using radio telescopes to study 20 tidal disruption events, Dr. Adelle Goodwin of Curtin University and co-author Dr. Andrew Mummery of the Institute for Advanced Study found that supermassive black holes fire off powerful jets in two distinct phases in their feeding cycle, noting that Radio is the only frequency where we can watch the jets and outflows as they’re moving outwards.
The first occurs when the black hole is feeding at very high rates. The second occurs hundreds to thousands of days after the star is first torn apart, when the feeding rate drops to about 2 percent of the maximum rate at which a black hole can swallow material.
“Sometimes, after it seems like they are done eating, they may get indigestion and they may let out a large radio ‘burp,’ These late-time radio burps can appear when the black hole eats too fast or eats too slowly, so you should always eat the right speed if you want to avoid indigestion.”
Kate Alexander, astronomer at the University of Arizona
That same threshold is already known to trigger burps from stellar-mass black holes, much smaller bodies about 10 to 50 times the mass of the sun. The research showed that black holes appeared to release jets at the same point in their feeding cycle regardless of size, according to findings published in Nature Astronomy.
Chemical Signatures Predict Future Flares
The data revealed that these delayed flares ignite at opposite extremes, either while the black hole is rapidly overgorging on gas or after its feeding rate has slowed to a crawl.
Unifying Physics Across Vast Mass Scales
This feeding mechanic operates identically across all scales, working the exact same way whether the black hole is a relative lightweight or a behemoth ranging from hundreds of thousands to billions of times the mass of our sun.
Understanding these precise mechanisms will enable scientists to narrow observation windows and free up precious telescope time moving forward.