GW170817 (nonfiction)

The GW170817 signal as measured by the LIGO and Virgo gravitational wave detectors.

GW170817 was a gravitational wave (GW) signal observed by the LIGO and Virgo detectors on 17 August 2017. The GW was produced by the last minutes of two neutron stars spiralling closer to each other and finally merging, and is the first GW observation which has been confirmed by non-gravitational means. Unlike the five previous GW detections, which were of merging black holes not expected to produce a detectable electromagnetic signal, the aftermath of this merger was also seen by 70 observatories on seven continents and in space, across the electromagnetic spectrum, marking a significant breakthrough for multi-messenger astronomy. The discovery and subsequent observations of GW170817 were given the Breakthrough of the Year award for 2017 by the journal Science.

The gravitational wave signal, designated GW170817, had a duration of approximately 100 seconds, and shows the characteristics in intensity and frequency expected of the inspiral of two neutron stars. Analysis of the slight variation in arrival time of the GW at the three detector locations (two LIGO and one Virgo) yielded an approximate angular direction to the source. Independently, a short (~ 2 seconds duration) gamma-ray burst, designated GRB 170817A, was detected by the Fermi and INTEGRAL spacecrafts beginning 1.7 seconds after the GW merger signal. These detectors have very limited directional sensitivity, but indicated a large area of the sky which overlapped the gravitational wave position. It has long been theorized that short gamma-ray bursts are caused by neutron star mergers.

An intense observing campaign then took place to search for the expected emission at optical wavelengths. An astronomical transient designated AT 2017gfo (originally, SSS17a) was found 11 hours after the gravitational wave signal in the galaxy NGC 4993[15] during a search of the region indicated by the GW detection. It was observed by numerous telescopes, from radio to X-ray wavelengths, over the following days and weeks, and was shown to be a fast-moving, rapidly-cooling cloud of neutron-rich material, as expected of debris ejected from a neutron-star merger.

Fiction cross-reference

• Crimes against astronomical constants
• Gnomon algorithm
• Gnomon Chronicles

Nonfiction cross-reference

• Gravity (nonfiction)
• Gravity wave (nonfiction)

External links:

• GW170817 @ Wikipedia