“Late Time Afterglow Observations Reveal a Collimated Relativistic Jet in the Ejecta of the Binary Neutron Star Merger GW170817” . This is the title of the study that won the seventh edition of the Aspen Institute Italia Award for collaboration and scientific research between Italy and the United States.
On August 17, 2017, the Virgo (in Italy) and LIGO (in USA) detectors observed for the first time the gravitational wave signal produced by the merger of two neutron stars. The cataclysmic event, occurring in a galaxy 130 million light years away, was also observed in different frequency bands of the electromagnetic spectrum (including X- and gamma-rays and infrared, optical, and radio signals). This marked the beginning of the era of “multi-messenger” astrophysics, based on the combination of gravitational waves and electromagnetic signals: a novel field of investigation that holds great potential in the coming years.
Among the different fundamental discoveries accompanying such an extraordinary event, it was possible to confirm that the merger of two neutron stars can launch a collimated energy outflow or jet powerful enough to produce a so-called “short Gamma Ray Burst”, ending decades of uncertainty about the origins of such energy explosions, which are among the most luminous in the universe.
By comparing electromagnetic observations collected within the first few months (since the initial gravitational wave detection) with advanced computer simulations, the winning research project marked a key step forward: it demonstrates the compatibility of the data with the hypothesis of a canonical collimated jet of energy analogous to any other short Gamma Ray Burst. In this case, it was observed not along the propagation direction of the jet itself, but from a different viewing angle. Further data collected in the following months definitively confirmed that the hypothesis supported in this work is indeed the correct one.
In the coming years, the gravitational wave and electromagnetic observation of many more neutron star mergers will allow for major steps forward in our understanding of these events and their extreme physical conditions. In this new journey, this winning research project will remain a reference point, while representing, more in general, a milestone in the field of relativistic astrophysics.
The authors of the study are:
- Davide Lazzati ¹
- Rosalba Perna ²
- Brian J. Morsony ³
- Diego Lopez-Camara ⁴
- Matteo Cantiello ⁵ ⁶
- Riccardo Ciolfi ⁷ ⁸
- Bruno Giacomazzo ⁸ ⁹ ¹⁰
- Jared C. Workman ¹¹
¹ Department of Physics, Oregon State University, Corvallis, Oregon, USA
² Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York, USA
³ Department of Astronomy, University of Maryland, College Park, Maryland, USA
⁴ CONACYT-Instituto de Astronomía, Universidad Nacional Autónoma de México, Mexico City
⁵ Center for Computational Astrophysics, Flatiron Institute, New York, New York, USA
⁶ Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey, USA
⁷ INAF, Osservatorio Astronomico di Padova, Padua, Italy
⁸ INFN–TIFPA, Trento Institute for Fundamental Physics and Applications, Trento, Italy
⁹ Physics Department, University of Trento, Trento, Italy
¹⁰ Department of Physics “Giuseppe Occhialini”, University of Milano-Bicocca, Milan, Italy
¹¹ Department of Physical and Environmental Sciences, Colorado Mesa University, Grand Junction, Colorado, USA
The research was published in Physical Review Letters 120, 241103 in 2018: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.241103