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Cosmic explosion reveals flaws in theories about universe


Published Nov 22, 2013

An international research team that includes members from Sweden's KTH Royal Institute of Technology and Stockholm University has observed one of the most powerful cosmic explosions yet measured. The results are difficult to explain with any existing model, showing that we have a long way to go before understanding the most extreme events in our universe.

These maps show how the sky looks at gamma-ray energies above 100 million electron volts (MeV). Left: The sky during a three-hour interval prior to the detection, showing the normal appearance of the sky. Right: A three-hour interval starting 2.5 hours before the burst and ending 30 minutes into the event, illustrating its brightness relative to the rest of the gamma-ray sky. The gamma-ray burst GRB 130427A was located in the constellation Leo near its border with Ursa Major, whose brightest sta

The findings are published in two articles in this week's edition of the journal Science.

"Gamma-ray bursts are the most luminous explosions in the universe, and we think they occur when massive stars collapse. Yet since they are so distant, we normally think of them as extremely faint. This event shows us that the universe is full of surprises," says Magnus Axelsson, astronomer at Stockholm University and one of the researchers behind the study.

Shortly after 9:47 a.m. (CET) on April 27 this year, all available telescopes turned to the same patch of sky. The brightest gamma-ray burst to date had just been detected. The flash of radiation was so strong that one of the detectors on board the Fermi telescope was unable to keep up. Perhaps even more astonishing was how long the burst lasted. The high-energy radiation from a normal gamma-ray burst is usually over in a matter of minutes. This time the photons kept on coming for many hours. This is very difficult to explain using the standard models.

Magnus Axelsson, astronomer at Stockholm University.
Felix Ryde, docent in astroparticle physics at KTH

Axelsson compares observing gamma-ray bursts to looking at a distant lighthouse on a cloudy night at sea. "We count every photon, or particle of light, gathering as much information as we possibly can. The question we want to answer is where the radiation comes from, like trying to see the glowing wire in the lighthouse beacon. But with this event, it's as if the clouds part and the full moon comes out - suddenly we are flooded in light and previously hidden details stand out clear. What I find most exciting is that the model most of us believed in is unable to explain what we see!"

Felix Ryde, head of the participating group at KTH, agrees. "This gamma-ray burst breaks all the records; the most luminous, the highest measured energy and the longest lasting gamma-ray emission. But our studies show that it's not special in any way, it just happened to be very close. This means that if our models don't work here, they are probably also incorrect for other gamma-ray bursts. So we need to keep working to revise our theories. The key to understanding the physics behind the radiation is to look at the details, and that's why this event is so important."

The work presented today has been performed within the international collaboration behind the Fermi satellite, which was launched in 2008. The Swedish participants come from KTH and Stockholm University.

For more information contact Felix Ryde, KTH, +46 70-495 75 15,  or Magnus Axelsson, Stockholm University, +46 72-204 19 71, .