The brightest light in the Universe


Telescopes pick up the afterglow of a violent explosion.


The fading afterglow of GRB 190114C and its home galaxy were imaged by the Hubble Space Telescope in February and again in March. The difference between the images reveals a faint, short-lived glow (centre of the green circle) located about 800 light-years from the galaxy’s core.

NASA, ESA, and V. Acciari et al. 2019

A violent explosion in a galaxy seven billion light-years away has broken the record for the brightest source of high-energy light in the Universe.

The gamma ray burst (GRB), now known as GRB 190114C, was detected on 14 January this year by two space satellites: the Neil Gehrels Swift Observatory and the Fermi Gamma-ray Space Telescope.

Its significance has now been confirmed by more than 300 international scientists and reported in the journal Nature.

GRBs are the most violent explosions since the Big Bang and are thought to follow the collapse of massive stars or the merging of neutron stars or black holes in distant galaxies. They release an energy comparable to that emitted by the Sun during its entire life.

Within seconds of GRB 190114C’s detection, its coordinates were sent to astronomers around the world, including those at the two 64-tonne Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescopes in the Canary Islands.

They immediately detected particles of light – or photons – from the afterglow that clocked in at between 0.2 and one teraelectron volts (TeV): equivalent to the amount of energy released by proton collisions in the Large Hadron Collider, the most powerful particle accelerator on Earth.

“It’s a trillion times more energetic than visible light,” says co-author Gemma Anderson, from the Curtin University, Australia, node of the International Centre for Radio Astronomy Research. “It makes GRB 190114C the brightest known source of TeV photons in the Universe.”

Anderson says the high-energy light was likely caused by the blast wave of material from the GRB hitting the surrounding environment. “The photons probably weren’t generated in the explosion itself,” she adds.

GRBs appear in the sky without warning, about once a day. They usually only last a few seconds, but their afterglow can be observed by telescopes like MAGIC for several minutes, and by radio telescopes for months or even years.

The researchers say the new results, together with a very complete multi-wavelength overview, provide the first unequivocal evidence for a distinct emission process in the afterglow.

It is likely, they add, that the high-energy light is emitted by the “inverse Compton process”, where the highest-energy electrons in the jet crash into lower-energy gamma rays and boost them to much higher energies.

  1. https://swift.gsfc.nasa.gov/
  2. https://fermi.gsfc.nasa.gov/
  3. https://www.nature.com/articles/s41586-019-1754-6
  4. https://www.mpp.mpg.de/en/research/astroparticle-physics-and-cosmology/magic-and-cta-gamma-ray-telescopes/magic/
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