Updated

Updated · Space.com · Aug 21

Astronomers Confirm 12 Remnant Radio Galaxies With 12-Million-Year Average Fade Age

Updated

Updated · Space.com · Aug 21

Astronomers Confirm 12 Remnant Radio Galaxies With 12-Million-Year Average Fade Age

Q: Could the fading ghosts of these giant radio galaxies actually be sleeping giants waiting to re-ignite?

Yes—some likely are, but this study does not show that the 12 confirmed remnants are already re-igniting. What the new observations show is that these galaxies are in a shutdown phase: their central black holes are no longer feeding jets strongly enough to keep the giant radio lobes bright, and the lobes are aging and fading. The spectral data from MeerKAT, LOFAR and the VLA indicate remnant ages of about 8 million to 42 million years, with a typical age near 12 million years, so many appear to be relatively young “dying” systems. That said, radio galaxies are known to be episodic. Other research and simulations cited alongside this work show the transition from active to remnant is gradual, not an instant stop. In some environments, especially lower-density groups, lobes can stay overpressured and continue coasting for around 10 million years after the jets switch off. Separate evidence from “double-double” radio galaxies also shows that black holes can restart jet production after a quiet interval. So the “ghosts” could indeed be sleeping giants in some cases. If fresh fuel later reaches the supermassive black hole, new jets could switch back on, sometimes inside the old fading lobes. But for these specific XMM–LSS objects, the current data mainly support a fading remnant interpretation, not proof of imminent revival. Future deep SKA-era radio surveys should be able to catch more systems in the act of restarting.

3 articles · Updated · Space.com · Aug 21

12 of 14 suspected objects in the XMM-LSS field were confirmed as remnant radio galaxies, giving astronomers a newly identified population of fading systems whose central black hole-driven jets have shut down.
MeerKAT, the Jansky Very Large Array and LOFAR let the team track how the lobes' radio emission weakens as particles age, showing the stalled engines can no longer replenish the plasma outflows.
8 million to 42 million years of fading were measured across the remnants, with a 12 million-year average that is younger than previously measured remnants and suggests a short-lived population had been missed.
The 12 remnants also span multiple evolutionary stages—from jets that only recently switched off to long-powered-down systems—offering a clearer picture of how radio galaxies die and how supermassive black holes govern that cycle.