Last updated November 29, 2019 at 9:05 am
“A typical burst releases as much energy in a few seconds as the Sun will in its entire 10-billion-year lifetime.”
Why This Matters: Astronomers are on the verge of understanding the most epic explosions in the universe.
A violent explosion in a distant galaxy has broken the record for the brightest source of high-energy light in the universe.
The light was emitted by a gamma ray burst, a brief but powerful cosmic explosion in a galaxy seven billion light-years away. It clocked in at a trillion times more energetic than visible light.
Astronomer Gemma Anderson from the Curtin University node of the International Centre for Radio Astronomy Research was one of a worldwide group of astronomers who worked on the discovery. The results have been published in the journal Nature.
Gamma ray bursts are among the most powerful explosions in the universe, she says. “They are likely produced by a massive star being blown apart in a supernova, with the resulting explosion leaving behind a black hole.”
As the star’s core collapses to become a black hole, jets of particles blast outwards at nearly the speed of light. They produce an initial burst of gamma rays – the most energetic form of light – that typically lasts about a minute.
“A typical burst releases as much energy in a few seconds as the Sun will in its entire 10-billion-year lifetime,” says Anderson. However, astronomers are still unsure how they create such an energetic burst.
Telescopes snap into action to capture burst
Astronomers first saw the GRB phenomenon in the late 1960s when spy satellites started detecting emissions from outer space. The blasts appear, without warning, at random locations in the sky about once a day.
Within seconds the satellites fired off an alert to astronomers around the world with the coordinates of the signal, dubbed GRB 190114C.
One facility to respond was the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) observatory, located in the Canary Islands, Spain. Both of its 17-meter, 64-ton telescopes automatically turned to the site of the fading burst. In less than a minute, they had begun capturing the most energetic gamma rays ever seen from these events.
“The telescopes were able to observe the burst within 50 seconds of it appearing in the sky,” says Razmik Mirzoyan, who works on MAGIC.
In those first seconds after MAGIC locked onto the signal, the telescopes detected particles of light – or photons – from the afterglow that clocked in at between 0.2 and 1 teraelectron volts (TeV).
“It’s a trillion times more energetic than visible light,” says Anderson. It is the first time such high-energy radiation has been detected from a gamma ray burst.
“It makes GRB 190114C the brightest known source of TeV photons in the universe.”
“The bursts themselves usually only last a few seconds,” she adds. “But they have an afterglow that can be observed by telescopes like MAGIC for several minutes, and by radio telescopes for months or even years.”
Gamma rays probably not from explosion itself
Alerted by Mirzoyan to what MAGIC was seeing, telescopes around the world also swung into action. This worldwide network worked together to pinpoint where the burst had originated and its physical attributes.
That included observations of radio waves by Anderson and collaborators in Australia using the Australia Telescope Compact Array (ATCA).
Anderson says the high-energy light was likely caused by the blast wave of material from the gamma ray burst hitting the surrounding environment.
“The photons probably weren’t generated in the explosion itself,” she says.
Instead, the rays may come from the magnetic field at the leading edge of the jet. High-energy electrons caught up in the fields may crash into lower-energy gamma rays and boost them to much higher energies.
Second GRB discovery also captures high energy gamma rays
Incredibly, the measurements by MAGIC weren’t the only recent recordings of a gamma ray burst.
A second paper also published in Nature describes a different burst, which Fermi and Swift both discovered on July 20, 2018.
Ten hours after their alerts, the High Energy Stereoscopic System (H.E.S.S.) in Namibia pointed its 28-meter gamma-ray telescope to the location of the burst, called GRB 180720B.
While the burst wasn’t as high energy as the one discovered by MAGIC, it still released Very High Energy gamma rays with energies up to 440 GeV.
Even more remarkable, the glow continued for two hours following the start of the observation.
“Our observation of a gamma-ray burst suggests the accelerated particles creating the gamma-rays still exist or are created a long time after cosmic explosions,” says the University of Adelaide‘s Gavin Rowell, who is part of the H.E.S.S. team.
Catching this emission so long after the GRB’s detection is both a surprise and an important new discovery.