From Manu Garcia: ” LIGO, Boxing Day”

Manu Garcia, a friend from IAC.

The universe around us.
Astronomy, everything you wanted to know about our local universe and never dared to ask.

Author: Manu Astrologus – Update: 21/5/17
Second detection of gravitational waves.

Artist illustration represents two binary black hole systems for molten GW150914 (left) and GW151226 (right). Pair of black holes are shown together in this illustration but actually detected at different times and in different parts of the sky. The images have been scaled to show the difference in the masses of black holes. In the event GW150914 , black holes were 29 and 36 times the mass of the sun, while GW151226 , the two black holes weighing between 14 and 8 solar masses. Image Credit: LIGO / A. Simonnet.

Caltech/MIT Advanced aLigo Hanford, WA, USA installation

Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

ESA/eLISA the future of gravitational wave research

The two gravitational wave detectors LIGO Hanford Washington and Livingston Louisiana have captured a second robust signal of two black holes in their final orbits then coalescence, fusion <>, in a single black hole. This event, called GW151226 , was seen on 26 December at 3:38:53 (coordinated universal time, also known as Greenwich Mean Time) near the end of the first LIGO observation period ( “O1”), and it was immediately nicknamed “the boxing day event”.

As the first detection LIGO , this event was identified few minutes after passage of the gravitational wave. Subsequently, careful studies of tools and environments around the observatories showed that observed in the two detectors signal was truly distant black holes, about 1,400 million light years away, coinciding with the same distance as the first detected signal. However, the Boxing Day event differed from the first observation of gravitational waves LIGO in some important ways.

The gravitational wave detectors came to the two almost simultaneously, indicating that the source is somewhere in heaven ring halfway between the two detectors. Knowing our pattern detector sensitivity, we can add that was a little more likely overhead or underfoot instead of west or east. With only two detectors, however, we can not reduce it much more than that. This differs from the first detected signal LIGO ( GW150914 , from 14 September 2015), which came from the southeast, hitting the detector Louisiana before Washington.
The two black holes merged in the event of Boxing Day were less massive (14 and 8 times the mass of our sun) than those observed in the first detection GW150914 (36 and 29 times the mass of our sun). While this made the weakest signal that GW150914 , when these lighter black holes were combined, changed its signal at higher frequencies that bring in the sensitive band LIGO before the fusion event observed in September. This allowed us to observe more orbits that the first detection-orbits about 27 in about one second (this compares with only two tenths of observation in the first detection). Combined, these two factors (smaller and observed masses orbits) were keys to allow LIGO detect a weaker signal. They also allowed us to make more accurate comparisons with General Relativity. Note: the signal again coincides with Einstein’s theory.
Last but not least, the event Boxing Day revealed that one of the first black holes was spinning like a top – and this is a first opportunity for LIGO can state this with confidence. A rotating black hole suggests that this object has a different story – p. Maybe “he sucked” the mass of a companion star before or after a star collapsing to form a black hole, achieving rotated in the process.

With these two detections confirmed, along with a third probable detection made in October 2015 (believed to also could be caused by a pair of coalescing black holes) we can now begin to estimate the rate of coalescence of black hole in the universe based not in theory, but in actual observations. Of course, with only a few signs, our estimate is large uncertainties, but maybe now is between 9 and 240 binary coalescence of black hole Gigaparsec cubic per year, or about one every 10 years in a volume a trillion times the volume galaxy of the Milky Way. Happily, in its first months of operation, they advanced LIGO detectors were sensitive enough to dig deep enough into space to see about an event every two months.

Our next observation interval – Watching Round # 2, or “O2” – will begin in the fall of 2016. With improved sensitivity, we expect to see more coalescence of black holes and possibly detect gravitational waves from other sources, such as mergers of binary star neutrons. We also expect the Virgo detector will join us later in the race O2. Virgo will be enormously useful for locating sources in the sky, collapsing the ring until a patch, but also helping us to understand the sources of gravitational waves.

LIGO releases its data to the public. This policy of open data allows others to analyze our data, ensuring that LIGO and Virgo collaborations do not lose anything in their analyzes, and hoping that others might be even more interesting events. Our data are shared in the Open LIGO Science Center. GW151226 has its own page there.

We invite you to stroll the LIGO Laboratory website where you will find charts to help you understand the observation of Boxing Day, links to the press release and suggestions for scientific papers if you want to deepen further. There you will also find links to the website of LIGO Scientific Collaboration, and our collaboration sister, Virgo, which are essential for these scientific results.


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