Starship Asterisk*

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The LIGO Scientific Collaboration and the Virgo collaboration report the first joint detection of gravitational waves with both the LIGO and Virgo detectors. This is the fourth announced detection of a binary black hole system and the first significant gravitational-wave signal recorded by the Virgo detector, and highlights the scientific potential of a three-detector network of gravitational-wave detectors.

The three-detector observation was made on August 14, 2017 at 10:30:43 UTC. The two Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, and funded by the National Science Foundation (NSF), and the Virgo detector, located near Pisa, Italy, detected a transient gravitational-wave signal produced by the coalescence of two stellar mass black holes.

A paper about the event, known as GW170814, has been accepted for publication in the journal Physical Review Letters.

The detected gravitational waves—ripples in space and time—were emitted during the final moments of the merger of two black holes with masses about 31 and 25 times the mass of the sun and located about 1.8 billion light-years away. The newly produced spinning black hole has about 53 times the mass of our sun, which means that about 3 solar masses were converted into gravitational-wave energy during the coalescence. ...

• Physical Review Letters (accepted 25 Sep 2017) (preprint)

http://www.virgo-gw.eu/docs/GW170814/GW170814_press_release_en.pdf wrote:
<<Overall, the Universe volume which is likely to contain the source shrinks by
more than a factor 20 when moving from a two-detector network to a three-
detector network. The sky region for GW170814 has a size of only 60 square
degrees, more than 10 times better than for the two LIGO interferometers
alone; in addition, the accuracy with which the source distance is measured
benefits from the addition of Virgo.>>

FIG. 3: Localization of GW170814. The rapid localization using data from the two LIGO sites is shown in yellow, with the inclusion of data from Virgo shown in green. The full Bayesian localization is shown in purple. The contours represent the 90% credible regions. The left panel is an orthographic projection and the inset in the center is a gnomonic projection; both are in equatorial coordinates. The inset on the right shows the posterior probability distribution for the luminosity distance, marginalized over the whole sky.

Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky.
(Credit: Giuseppe Greco (Virgo Urbino group))