black hole

Zombie black hole reanimates and eats a star

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Aug 5, 2016, 9:42 AM EDT (Updated)

If you think a supermassive black hole asleep longer than Cthulhu suddenly devouring a star that woke it up is the stuff of science fiction, it’s real—as in, NASA real.

What sounds like a Lovecraftian myth happened 3.9 billion years ago in a galaxy so many light-years away that the evidence has just reached Earth. NASA’s Swift Satellite was recently able to detect X-rays from the dismembered star that touched down on our planet. Swift sent alerts to astronomers like a hyper-urgent text message heard round the world. The space-pocalypse, officially named Swift J1644+57, meant that a previously dormant black hole had gone Mount Etna on an unsuspecting star that caused it to violently flare up. In other words, these X-rays, or star innards, emitted in the event are proof that black holes which go into hibernation mode can and will wake if an immense amount of energy lurks close enough to the event horizon (aka the point of no return).

Supermassive black holes are the grim reapers of the galaxy. These astral corpses increase their dark powers by consuming passing stars and merging with other black holes. Unfortunately, there wasn’t enough energy in the universe to supply the gravitational feeding frenzy billions of years ago. Some 90% of black holes remain inactive as a result. Quiescent black holes, which is what scientists call these slumbering space beasts, never actually “died.” An autopsy of Swift J1644+57 reveals a monstrous outburst that is more scientifically referred to as a tidal disruption. Tidal force is a side effect of gravity that is triggered by the inconsistent gravitational pull exerted by one celestial body on another—meaning one side will always attract more mass. The crushing pull of gravity is also what shreds a star that creeps too close to the wrong side of a supermassive black hole.

X-ray images from Swift

Swift's X-ray image of the outburst is evidence of black holes behaving badly.


When X-rays flash from black hole-ravaged stars, they echo through the vastness of space, which is why NASA postdoctoral researcher Erin Kara is fronting a team of astronomers who are using these echoes, or reverberations, to better understand how a reanimated black hole enters back into consciousness. “While we don’t yet understand what causes X-ray flares near the black hole, we know that when one occurs we can detect its echo a couple of minutes later, once the light has reached and illuminated parts of the flow,” she says. These reflections shed light on the study of active black holes, but have never before been used to examine one that has just yawned awake from a sleep of over a billion years.

Stellar remains drawn towards a black hole are put through the medieval torture of being heated to millions of degrees before intense gravity pulls them past the point of no return. Until then, they orbit the black hole in a mass of enraged ions whose energy blazes in what known as an accretion disc. Kara’s team has found that the accretion disc of J1644+57 is not only thicker than most but seething with chaos. These findings can possibly illuminate more secrets hiding in the dark unknown of the space-time continuum. As Kara and her NASA colleagues state in Relativistic Reverberation in the Accretion Flow of a Tidal Disruption Event, “Tidal disruption events, where a star orbiting an otherwise dormant black hole gets tidally shredded and accreted onto the black hole, can provide a short, unbiased glimpse at the space-time around the other ninety per cent of black holes.”  

This means we earthlings still have an infinite number of black holes left to find—and opening the cold case files of more billion-year-old cases of stars that died from provoking black holes could give us a glimpse into explosive secrets of the primeval universe. 

(Via Sci Tech Daily)