GW170817: A Binary Neutron Star Merger

This discovery marks first cosmic event observed in both gravitational waves and light.

For the first time, astronomers have observed the gravitational waves – ripples in the fabric of space-time – and the light from the merger of two neutron stars. The event observed on August 17th 2017, at 12:41:04 UTC, marks the advent of multi-messenger astronomy which combines gravitational-wave and electromagnetic observations. Together, the complementary methods will enhance our understanding of extreme astrophysical events, and provide an unprecedented opportunity to probe the outcome of the collision of two neutron stars. Researchers at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute/AEI) in Potsdam and Hannover and at the Leibniz Universität Hannover played a central role in the discovery.

The videos and the images show a numerical simulation representing the binary neutron star coalescence and merger which resulted in the gravitational-wave event GW170817 and gamma ray burst GRB170817A. The two non-spinning neutron stars shown in the animations have 1.528 and 1.222 solar masses and follow the ALF2 equation of state (EOS). The employed parameters (total mass, mass ratio, spin and EOSs) are consistent with the detection made on the 17th of August by the LIGO/Virgo detectors. While only the gravitational wave signal emitted during the inspiral of the two neutron stars has been detected, the detection of electromagnetic counterparts, in particular of the kilonova and gamma ray burst, suggest a complicated evolution of the merger remnant with a possible hypermassive or supramassive neutron star phase and black hole formation as shown in the animation.

The animations show the gravitational wave signal with colors ranging from yellow to red with increasing strength, the density of the neutron stars from light to dark blue with densities in a range of 200 thousand to 600 million tons per cubic centimeter. Additionally, we present the matter which gets ejected from the system in purple. This ejected material is the source for the kilonova detected after the neutron star merger. Since the density of this unbound, ejected material is smaller than inside the neutron star, we also show material with densities as low as 600 tons per cubic centimeter. Finally, the black hole that forms after the collapse of the hypermassive neutron star is shown in gray.

In the video below we also show the strain of the gravitational wave signal in the bottom part of the video indicating the time evolution by a changing color. In the video the part of the signal after the merger has not been detected by LIGO and is plotted dashed. The postmerger evolution itself is highly uncertain and the presented animation marks one possible outcome.

Numerical Relativity Simulation: T. Dietrich (Max Planck Institute for Gravitational Physics) and the BAM collaboration
Scientific Visualization: T. Dietrich, S. Ossokine, H. Pfeiffer, A. Buonanno (Max Planck Institute for Gravitational Physics)

GW170817: Numerical relativity simulation of a binary neutron star merger

Simulation of the first cosmic event observed in both gravitational waves and light

In a short clip, we show the gravitational waves color blue to red with increasing amplitude. The neutron stars are colored red and are shown in the center region of the movie.

GW170817: Numerical relativity simulation of a binary neutron star merger

Simulation of the first cosmic event observed in both gravitational waves and light
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