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.”
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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.
The fading afterglow of GRB 190114C and its home galaxy were imaged by the Hubble Space Telescope on Feb. 11 and March 12, 2019. The difference between these images reveals a faint, short-lived glow (center of the green circle) located about 800 light-years from the galaxy’s core. Blue colors beyond the core signal the presence of hot, young stars, indicating that this is a spiral galaxy somewhat similar to our own. It is located about 4.5 billion light-years away in the constellation Fornax. (Click to enlarge) Credit: NASA, ESA, and V. Acciari et al. 2019
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.
However, on 14 January 2019, two satellites – the Neil Gehrels Swift Observatory and the Fermi Gamma-ray Space Telescope – each detected a sudden spike of gamma rays from the constellation Fornax.
Within seconds the satellites fired off an alert to astronomers around the world with the coordinates of the signal, dubbed GRB 190114C.
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Artist Impression: The MAGIC Telescopes detected the highest-energy gamma-rays from a Gamma-Ray-Burst following the alerts issued by Swift and Fermi. Credits: Superbossa.com and C. Righi.
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.
This illustration shows the set-up for the most common type of GRB. The core of a massive star (left) has collapsed and formed a black hole. This “engine” drives a jet of particles that moves through the collapsing star and out into space at nearly the speed of light. The prompt emission, which typically lasts a minute or less, may arise from the jet’s interaction with gas near the newborn black hole and from collisions between shells of fast-moving gas within the jet (internal shock waves). The afterglow emission occurs as the leading edge of the jet sweeps up its surroundings (creating an external shock wave) and emits radiation across the spectrum for some time — months to years, in the case of radio and visible light, and many hours at the highest gamma-ray energies yet observed. These far exceed 100 billion electron volts (GeV) for two recent GRBs. (Click to enlarge) Credit: NASA Goddard Space Flight Center
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.
