GW151226

The signal was detected by LIGO at 03:38:53 UTC when the Hanford detector triggered 1.1 milliseconds after the Livingston detector (since the axis between them was not parallel to the wave front ) ^[1] . The gravitational wave surge, which received the preliminary designation G211117, lasted almost a second and was recognized by an automatic tracking system for a minute. Subsequently, an offline analysis of the event was carried out, and after about a couple of days the participants of the collaboration knew that they really caught the second gravitational-wave surge. He was assigned a permanent designation GW151226 ^[2] (GW - short for English gravitational wave , "gravitational-wave", the number determines the date of registration of the event, [20] 15/12/26).

To isolate the signal from the noise of the LIGO and Virgo collaboration, the analysis was performed using two different methods. The assessment of reliability showed that false-positive signals of such intensity caused by random noise overlapping should occur less than once every 160 thousand years, and therefore the probability of detecting such a signal in a 45-day data series is less than 10 ⁻⁷ . According to the data of applied methods, the statistical reliability of the event exceeds 5 σ or 4.5σ (according to the first and second methods) ^[2] , which corresponds to the “opening threshold” generally accepted in physics.

Since the event took place on the night of December 26, the observatory employees called it a “Christmas present” ^{[3] [2]} .

On June 15, 2016, LIGO and Virgo observatories reported that they verified the signal. It was also announced that this is the world's second-identified gravitational wave signal after GW150914 ^{[1] [4]} .

The analysis revealed that the source of the signal is the fusion of two black holes with masses of 14.2 +8.3
−3.7 and 7.5 +2.3
−2.3 M _☉ , at a distance 440 +180
−190 megaparsek from the Earth. The result of the merger was a black hole weighing 20.8 +6.1
−1.7 M _☉ , and _{herewith a} mass equal to 1 +0.1
−0.2 M _☉ , turned into gravitational radiation ^{[1] [5]} . Thus, approximately 4.6% of the initial mass of two black holes passed into radiation.

Since a pair of detectors was used to estimate the distance, it was estimated only on the basis of the amplitude of the signal that arrived, without considering the orientation of the orbit plane relative to the direction behind the Earth. For this reason, the distance is not measured very accurately, with an error of almost 50%. The calculated distance of 440 megaparsecs corresponds to 1.4 billion light years, which corresponds to a red shift of 0.09 + 0.03
−0.04 ^{[2] [6]} .

To estimate the direction to the signal source, only the difference in the time of arrival of the signal to two detectors was used (without taking into account their relative response), and for this reason the direction is estimated very poorly - potential areas are “arcs for half the sky” ^{[2] [6]} . From geometric considerations it is obvious that in order to accurately determine the direction to the source, it is necessary to compare the time of registration of an event by three detectors. At the time of registration GW151226, the third detector (Virgo) was not working yet.

Regarding this event, the scientists of the LIGO and Virgo collaborations were able to reliably determine that at least one of the black holes before the merger had an angular momentum of rotation more than 20% of the maximum allowable, based on the general theory of relativity ^{[1] [7]} . The black hole formed after the merger rotated with an angular momentum of 0.74 + 0.06
−0.06 of the maximum possible angular momentum ^[1] . Black holes were smaller than those, the merging of which caused the first detected gravitational-wave surge GW150914 , and for this reason the event had less energy and was slower - about 1 second (the duration of GW150914 was 0.2 seconds). Thus, the detectors in this case could see more turns of black holes around each other at the final stage of the merger - 55 periods of oscillation (27 turns) per second with a frequency that grew from 35 to 450 Hz . For comparison, in the first event of the detection of gravitational waves there were 10 turns for 0.2 seconds ^{[1] [8] [2]} .

Event GW151226 speaks in favor of the fact that there are a greater number of double black holes in the Universe, with which mergers occur more often than previously assumed ^{[9] [10]} .

The measured gravitational wave surge is fully consistent with the predictions of the general theory of relativity for strong gravitational fields. Before the first two events detected with the help of LIGO, this theory was not subjected to direct experimental verification in strong fields (although it was tested with high accuracy in weak fields). The general theory of relativity underwent a more rigorous test during the second event ^{[5] [11]} . The longer duration of GW151226 made it possible to better limit some values ​​of the post-Newtonian formalism ^[2] .

Registration of the merger for the first time gave observational data on the rotation of black holes ^[2] .

The obtained GW151226 data provided information on two source black holes from the known six (three mergers), which provided data for estimating the distribution of black holes by mass for theories of the formation of black hole pairs of stellar masses. Also, the fact of the GW151226 event provided an opportunity to estimate the frequency of mergers (in the Universe) of black holes of comparable masses on the basis of observational data (previously there were only theoretical theoretical estimates) ^[2] .

For the first time, data on fusion of objects in a given stellar mass range were obtained. For example, they can be used to study binary X-ray stars ^[10] .

• Gravitational-wave astronomy
• Discovery of gravitational waves

• The elements are science news: LIGO caught new bursts of gravitational waves (Unidentified) . elementy.ru The date of circulation is January 24, 2017.
• LIGO Does It Again: A Second Robust Binary Black Hole Coalescence Observed Detection message on the LIGO website.
• LIGO Detected Gravitational Waves from Black Holes Message about the first detection of gravitational waves (English) .
• LIGO Open Science Center (eng.) . losc.ligo.org. The appeal date is February 1, 2017. - information and data about the event on the LIGO website.