Mysterious gamma ray burst 12 billion light-years away sparks questions

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Mar 29, 2017

Somewhere in the far reaches of space, a star gasped its dying breath and a black hole was born—then there was an enormous cataclysmic boom of gamma radiation to herald its arrival.

Superpowered gamma ray burst GRB170202 is an explosive find. GRBs are notoriously difficult to trace because gravitational wave observatories don’t yet have the technology to zero in on their exact locations. Even GRB170202’s blaze of glory was issuing from a galaxy far, far, far away, so far that the galaxy itself was swallowed up by blackness and not visible to telescopes. It only got scientists’ attention after its cosmic gamma rays collided with NASA’s Earth-oribiting Swift satellite and prompted an automatic alert that told the University of Washington’s Zadko Telescope to record the phenomenon. What Zadko imaged was astounding. An outburst with the brightness of a million stars emerged from what previously appeared to be a dark void—if only for under a minute.

Gamma ray bursts are optical transients, meaning that they materialize and then vanish from the sky (and visibility) extremely fast, never to be seen again. The Very Large Telescope in Chile was able to measure distance between our planet and the origin of the outburst using the spectrum of light from its optical afterglow. Just to give you an idea of how long ago 12 billion years, which is how long it took for the light to travel to Earth, actually is, the universe has quadrupled in size since then.

This light curve from the Zadko telescope shows the superfast evolution—and fading—of GRB170202.

GRB170202 was more than just a cosmic flash. Bursts like this indicate new black holes coming into being, and you know the birth of a black hole is underway when an intense flash of gamma radiation is followed by an optical transient. This funeral of fireworks results from the demise of a star so massive that it pretty much cannibalized itself by burning up its fuel within only tens to hundreds of thousands of years (if that doesn’t exactly sound like an early death, our sun has been shining for billions of years). The star’s gravitational collapse into a black hole happens in seconds.

Despite the infinite number of black holes out there, these events are rare because most stars in their death throes are unable to produce such an onslaught of gamma rays. GRBs can only happen when the star in question is tens of solar masses, rotates rapidly, and has a ridiculously strong magnetic field. They are also extremely valuable to researchers determining the universe’s black hole birth rate. While most of the resulting black holes either ravage unsuspecting stars and planets alone or merge with other black holes, those that are the astral corpses of neutron stars have the potential to really illuminate science. GRBs that flash in the wake of neutron star collisions and are coincidentally detected with gravitational waves could give invaluable insight into the physics of black hole formation.

While there is still only so much that telescopes can see, phenomena like GRB170202 keep illuminating the astrophysical mysteries black holes may be hiding.

(via Phys.org)