GW151226, the second event


The GW151226 event

On December 26, 2015 at 03:38:53 UTC, the LIGO and Virgo scientists have observed gravitational waves for the second time. The second event, labeled GW151226, was detected by the twin Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, USA.

As for the first event, GW150914, this one is consistent with the merger of two black holes. However, in this event the black hole masses are slightly smaller – 14 and 8 solar masses, producing a more massive black hole of 21 solar masses.

Gravity Waves StillImage

Image credit: LIGO/T. Pyle
This illustration shows the merger of two black holes and the gravitational waves that ripple outward as the black holes spiral toward each other. The black holes—which represent those detected by LIGO on Dec. 26, 2015—were 14 and 8 times the mass of the sun, until they merged, forming a single black hole 21 times the mass of the sun. In reality, the area near the black holes would appear highly warped, and the gravitational waves would be difficult to see directly.


This means that during the merger, which occurred approximately 1.4 billion years ago, mass roughly equivalent to the Sun was converted into gravitational waves. The signal comes from the last 27 orbits of the black holes before they merged.  The signal arrived in the Livingston detector about 1.1 milliseconds before reaching the Hanford detector: in this way the position of the source is roughly determined.

Here below we collect some useful resources about GW151226

Discovery Paper on Physical Review Letters:

Full “Observation Run 1” (September 2015 -> January 2016) binary black hole search:

Binary Black Hole Mergers in the first Advanced LIGO Observing Run (posted on arXiv)

VIRGO-related Press Releases

Webcast of the June 15, 2016 LIGO-Virgo press conference

Link to LIGO Press material

Press Review related to GW151226

Here is a selection of articles and stories appeared in Europe about the second announcement:











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