While the European Space Agency’s Integral satellite was observing the sky, it witnessed an intense burst of gamma rays that illuminated the nearby galaxy M82, 12 million light years away, for about a tenth of a second: the eruption came from a rare magnetar, a young neutron star that is extremely compact and has a very strong magnetic field, as the international research group led by the National Institute of Astrophysics published in the journal Nature. The Universities of Milan-Bicocca, the State University of Milan, of Insubria and the Iuss Higher University School of Pavia participated in the study. This is the first solid confirmation of a phenomenon of this type outside the Milky Way.
Just 13 seconds after the explosion was detected, an alert was sent to astronomers around the world. “We immediately realized that it was a special notice,” says Sandro Mereghetti of INAF in Milan, who led the study. ESA’s Xmm-Newton space telescope was therefore immediately mobilised, which a few hours later observed the same region of sky in search of a residual glow in the X-rays, which would have been present if the phenomenon had been caused by clash between two neutron stars: but the telescope found no traces, as did others on the ground, including the Italian National Telescopio Galileo, located on the Spanish island of La Palma.
“Without signals in X-rays and visible light, and without gravitational waves measured by detectors on Earth – adds Mereghetti – we are certain that the signal came from a magnetar”, a type of star that can occasionally emit these gigantic flashes of energy. In the past 50 years, only three such flares have been detected within the Milky Way, and this latest one is the first firmly confirmed to come from another galaxy.
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