Superluminal motion of a relativistic jet in the neutron-star merger GW170817
Introductory text in journal, 2018

The binary neutron-star merger GW1708171was accompanied by radiation across the electromagnetic spectrum2and localized2to the galaxy NGC 4993 at a distance3of about 41 megaparsecs from Earth. The radio and X-ray afterglows of GW170817 exhibited delayed onset4–7, a gradual increase8in the emission with time (proportional to t0.8) to a peak about 150 days after the merger event9, followed by a relatively rapid decline9,10. So far, various models have been proposed to explain the afterglow emission, including a choked-jet cocoon4,8,11–13and a successful-jet cocoon4,8,11–18(also called a structured jet). However, the observational data have remained inconclusive10,15,19,20as to whether GW170817 launched a successful relativistic jet. Here we report radio observations using very long-baseline interferometry. We find that the compact radio source associated with GW170817 exhibits superluminal apparent motion between 75 days and 230 days after the merger event. This measurement breaks the degeneracy between the choked- and successful-jet cocoon models and indicates that, although the early-time radio emission was powered by a wide-angle outflow8(a cocoon), the late-time emission was most probably dominated by an energetic and narrowly collimated jet (with an opening angle of less than five degrees) and observed from a viewing angle of about 20 degrees. The imaging of a collimated relativistic outflow emerging from GW170817 adds substantial weight to the evidence linking binary neutron-star mergers and short γ-ray bursts.


K. Mooley

National Radio Astronomy Observatory Socorro

California Institute of Technology (Caltech)

A. Deller

ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav)

Swinburne University of Technology

O. Gottlieb

Tel Aviv University

E. Nakar

Tel Aviv University

G. Hallinan

California Institute of Technology (Caltech)

S. Bourke

Chalmers, Space, Earth and Environment

D. A. Frail

National Radio Astronomy Observatory Socorro

A. Horesh

The Hebrew University Of Jerusalem

A. Corsi

Texas Tech University at Lubbock

K. Hotokezaka

Princeton University


0028-0836 (ISSN) 1476-4687 (eISSN)

Vol. 561 7723 355-359

Subject Categories

Subatomic Physics

Meteorology and Atmospheric Sciences

Astronomy, Astrophysics and Cosmology


Onsala Space Observatory



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