The LIGO and Virgo collaborations have announced the first detection of a binary neutron star merger, also detected as a Gamma-Ray Burst by the Fermi satellite. This common detection confirms theoretical predictions and mark a new page in multimessenger astronomy. ULB scientists have searched for a neutrino counterpart that would increase even more our understanding of this newly observed astrophysical phenomenon.

Predicted a century ago by Albert Einstein as part of his general theory of relativity, gravitational waves were first observed in September 2015 by the LIGO collaboration during the merging of two black holes. Repeatedly detected since then, the waves kept delivering precious information about our Universe.
The scientific community has announced today the first detection of a binary neutron star merger (BNS). Lighter than the black holes now commonly observed by the interferometers, the neutron stars are surrounded of matter. The acceleration of this matter could potentially create electromagnetic and neutrino emissions from the astrophysical event.

These theoretical predictions were confirmed by the Fermi satellite, which has detected light coming from the BNS 2 seconds after the gravitational waves. The signal, a burst of high energetic photons, was consistent with the emission from a Gamma-Ray Burst (GRB). This first joint detection marks the starting point of multimessenger astronomy and promises an even brighter future for the field of astroparticle physics.

Worldwide scientists have been searching for a neutrino counterpart, predicted by state-of-the-art models on GRBs and BNS. Among them, Dr. Kevin Meagher, scientist at the Interuniversity Institute for High Energy (ULB-VUB) in Brussels and member of the IceCube Neutrino Observatory. Dr. Meagher has developed a process allowing to search for astrophysical neutrinos in a realtime mode, turning IceCube into a telescope able to observe any interesting part of the sky on command. "This is very exciting because for a long time we had suspected that neutron star merging was the cause of gamma-ray bursts but we didn't have direct evidence. Now, we have very compelling evidence" says Meagher.

Detecting a GRB, gravitational waves and neutrino events may have been too much to ask at once and no neutrinos were observed. Dr. Juan Antonio Aguilar Sánchez, principal investigator of the ULB group, adds "The observation of a BNS is a remarkable milestone in gravitational wave astronomy, and although IceCube did not detect any coincident neutrino this time we are ready for the next BNS event".
The team, at the front of multimessenger astronomy, will continue chasing these elusive neutrinos and pursue the international effort to elucidate the remaining secrets of our Universe.

About the LIGO detectors

The Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo interferometer have been designed to open the field of gravitational-wave astrophysics providing direct detection of gravitational waves. The multi-kilometer-scale detectors are located in Hanford, Washington, USA and in Livingston, Louisiana, USA for the LIGO experiment while the Virgo detector is operating in Pisa. The LIGO interferometers have operated in unison to detect the first gravitational waves on September 14, 2015. The principal investigators of the LIGO experiment are the laureates of the 2017 Nobel prize in physics. More info: https://www.ligo.caltech.edu, http://www.virgo-gw.eu

About the IceCube Neutrino Observatory

The IceCube Neutrino Observatory is a cubic kilometer detector buried in the ice of the South Pole, Antarctica. Since the breakthrough of the first observation of astrophysical neutrinos in 2013, IceCube scientists have focus their effort on pushing the limits of the possible. The international collaboration has set several noteworthy limits on, among others, the existence of sterile neutrinos as well as competitive measurements of neutrino oscillation parameters. IceCube has also joined the worldwide multimessenger effort studying the highest energetic events in our Universe. More info: https://icecube.wisc.edu

About the IIHE

The Interuniversity Institute for High Energies is a common service to ULB and VUB. Its main topic of research is the physics of elementary particles using the high-energy particle accelerators and experimental facilities at CERN (Switzerland) as well as on non-accelerator experiments such as SoLid at SCK•CEN (Belgium), JUNO in China and IceCube at South Pole. Created in 1972, this institute has played a key-role in the Higgs boson discovery in 2012 in addition to provide many valuable contributions to astroparticle and particle physics. More info: http://w3.iihe.ac.be

Contact:
Juan Antonio Aguilar Sánchez, juaguila@ulb.ac.be
Kevin Meagher, kmeagher@ulb.ac.be

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