Black Holes Are Messy Eaters. Now We Have the Radio Receipts.

Some black holes keep broadcasting years after they've finished tearing a star apart, long after astronomers assumed the show was over.

Black holes were traditionally thought to go silent after a brief flare of activity. Now some are being observed emitting new bursts of energy years after devouring a star. A team led by Kate Alexander of the University of Arizona tracked 31 of these star-shredding events using the Very Large Array in New Mexico, and found that a striking share of them light up again in radio waves months, or even years, past the initial blast.

These events are called tidal disruption events, or TDEs. They occur when a star ventures too close to a black hole and is torn apart by its immense gravitational forces. Typically, about half the star's matter is ejected outward while the remainder forms a glowing accretion disk that spirals inward, briefly illuminating the cosmos across various wavelengths.

What the new research reveals is that the show isn't over when the light fades. Part of the material falling toward the black hole gets thrown back outward instead, launched as jets or winds from just outside the event horizon, and when that ejected matter collides with gas already surrounding the black hole, the impact triggers shock waves that glow in radio. The delay between the meal and the burp isn't random, either. Researchers found these late-time radio flares can appear whether a black hole eats too fast or too slowly. Pace matters, apparently, even at the edge of oblivion.

The assumption that TDEs release their energy primarily in the first few months is wrong. Astronomers have been closing the book on these events well before the last chapter.

Read the full story at Universe Today, June 25, 2025

Hot Take: We tend to picture black holes as unstoppable cosmic vacuum cleaners. Turns out some are more like giant babies with colic: they eat a star, spend years complaining about it, and finally let out a radio burp that astronomers can hear.