Scientists have detected a flash of light from across the Galaxy so powerful that it bounced off the Moon and lit up the Earth’s upper atmosphere.

This “giant flare” was the brightest explosion ever detected from beyond the Solar System. For over a tenth of a second the remarkable flare was actually
brighter than a full moon.

NASA and European satellites and ground-based telescopes around the world
detected the giant flare on 27 December 2004. Scientists from twenty
institutes joined the observations. Two science teams report about this
unprecedented event in a forthcoming issue of Nature.

The light detected from the giant flare was far brighter in gamma rays than
visible light or X-rays. It was probably created by an unprecedented eruption on the surface of an exotic neutron star which is classed both as an ultra-magnetic magnetar and as a soft gamma repeater (SGR).

The designation of the neutron star that erupted is SGR 1806-20, about 50,000 light years from Earth in the constellation Sagittarius.

A number of important questions arise from this discovery:

  • Are some gamma ray bursts (thought to be very distant black-hole-forming
    star explosions) actually from neutron star eruptions in nearby galaxies?
  • What mechanism could unleash so much energy from a magnetar?
  • Could an even larger influx of gamma rays have caused mass extinction on
    Earth in the past?

    British astronomers have focused on studying the radio emission from the
    event, which was produced as the explosion ploughed into the surrounding
    matter at about 100,000 km per second, heating particles to extraordinary
    energies.

    Dr. Rob Fender of Southampton University is a co-author on a Nature paper
    describing the radio observations.

    “This is a once-in-a-lifetime event. We have observed an object only 20
    kilometres across, on the other side of our Galaxy, releasing more energy in
    a tenth of a second than the Sun emits in 100,000 years,” said Fender.

    “The next biggest flare ever seen from any soft gamma repeater was peanuts
    compared to this incredible December 27 event,” said Dr. Bryan Gaensler of
    the Harvard-Smithsonian Center for Astrophysics, lead author on the Nature
    paper.

    “Had this happened within 10 light years of us, it would have severely damaged our atmosphere and possibly have triggered a mass extinction.

    Fortunately there are no magnetars anywhere near us.”

    “These neutron stars have magnetic fields hundreds of times more powerful
    than any other objects in the universe. We may be seeing a massive release
    of magnetic energy during a ‘starquake’ on the surface of the object,” added Dr.Maura McLaughlin of the University of Manchester, also a co-author
    on the Nature paper.

    Radio observations of the neutron star continue around the world, including
    the UK’s Multi-Element Radio-Linked Interferometer Network (MERLIN) and the
    Joint Institute for VLBI in Europe.