“What’s incredibly unusual about [these events] is that the objects came back to life, like a zombie.”
When a hapless star ventures too close to one of the supermassive black holes that lurk at the center of galaxies, it’s torn to shreds and stretched like spaghetti. In this so-called tidal disruption event , the black hole dines on the stellar remnants, which wrap around the black hole’s belly in an accretion disk. During the feast, the black hole can glow brighter than a supernova for months, before returning to a quiet state of hibernation.
Most of the few dozen known TDEs have been detected from the optical light or x-rays emitted in the initial feast. But, “Radio is now playing a very important role” in understanding TDEs, says astronomer Igor Andreoni of the Joint Space-Science Institute. Black holes generate radio waves by expelling plasma—pumping it out in polar jets or belching out material that crashes into surrounding gas. But these outflows normally take place during a TDE, shortly after the black hole rips apart its meal.
that launched more than 2 years after the black hole’s initial snack. “It’s a pretty exceptional case,” Cendes says., Sfaradi claims in the 10 July issue of. These tandem emissions are sometimes seen in so-called x-ray binaries—in which star-size black holes suck gas away from a paired star—hinting that the mechanisms may be related, Horesh says.
Tchekhovskoy agrees—and he’s got models that demonstrate the behavior. He and his colleagues ran computer simulations of accretion disk evolution and found they canin which jets can form efficiently. The key moment comes when the accretion disk is still dense enough to fuel jets, but not so dense as to reabsorb the generated radio waves. Perhaps that’s why we’re seeing these delayed bursts, he says—“We’re just waiting for the gas to have the right density.
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