– University of Copenhagen

The dawn of multimessenger astronomy

Today, the LIGO and Virgo collaborations have announced the detection of a new gravitational wave event, GW170817, which constitutes the first time that a binary neutron star merger has been detected with the LIGO observatory. This unique observation is even more compelling since the same collision was seen by the Fermi and INTEGRAL satellites as a result of a short gamma-ray burst (GRB) and, subsequently, across the electromagnetic spectrum, with radio, optical, and X-ray detections. These observations made it possible for the first time to pinpoint the source location of a gravitational wave event. The source was found to be in a galaxy 130 million light years away, known as NGC 4993.

The combined gravitational wave and gamma-ray observation of this event tells us that there was particle acceleration by the source, which provides insight into the merger process and also means that very high energy neutrinos might have been produced. The detection of neutrinos would reveal even more information about the merger, including the density and energy of the hadrons involved and the energy dissipation mechanisms.

In a joint effort by the ANTARES, IceCube, Pierre Auger, LIGO, and Virgo collaborations, scientists have searched for neutrino emission from this merger. The search looked for neutrinos in the GeV to EeV energy range and did not find any neutrino in directional coincidence with the host galaxy. The nondetection agrees well with our expectation from short GRB models of observations at a large off-axis angle, which is most likely the case for the GRB detected in conjunction with GW170817. These results are being submitted to The Astrophysical Journal.

Artist's illustration of two merging neutron stars. (NSF/LIGO/Sonoma State University/A. Simonnet)


The detection of a gravitational wave event is always exciting news for astrophysicists, but having one also confirmed for the first time by other instruments that detect photons is even more exciting. It marks the beginning of a new era of multimessenger astrophysics. For IceCube scientists, it is another step toward the time when cosmic events will be detected and studied with neutrinos, light, and gravitational waves together.

Mohamed Rameez, who is a member of the IceCube group at the Niels Bohr Institute, helps to maintain the Astrophysical Multimessenger Observatory Network (AMON). This alert system allows for a fast distribution of astrophysical candidate events between a diverse array of different types of observatories. Individual candidate events have already a high probability to be messengers of astrophysical sources. However, a statistically significant detection of sources would require an immediate "follow-up" observation by AMON partners, coincident with the event time and position. This alert system is crucial in the case of gamma-ray detectors and optical telescopes, which cannot see the entire sky simultaneously, and thus need to be reoriented to point in a specific direction.

IceCube has already proven the existence of an extragalactic flux of astrophysical neutrinos. With a growing network of gravitational-wave detectors, it is expected that many more binary neutron star mergers will be discovered in the near future, expanding the capability to study these sources through high-energy neutrinos with IceCube.

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The IceCube Neutrino Observatory, embedded down to 2.5 km deep under the South Pole, is the world's largest and most sensitive ‘telescope' for high energy neutrinos. With a cubic kilometer of instrumented ice it is the largest particle detector in the world.

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People at IceCube