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March 17, 2016

LIGO opens new window on the universe (Image 4)

The approximate location of the source of gravitational waves detected on Sept.14, 2015, by the twin Laser Interferometer Gravitational-wave Observatory (LIGO) facilities is shown on this sky map of the Southern Hemisphere. The colored lines represent different probabilities for where the signal originated. The purple line defines the region where the signal is predicted to have come from, with a 90 percent confidence level; and the inner yellow line defines the target region at a 10 percent confidence level. The gravitational waves were produced by a pair of merging black holes located 1.3 billion light-years away. A small galaxy near our own, called the Large Magellanic Cloud, can be seen as a fuzzy blob underneath the marked area, while an even smaller galaxy, called the Small Magellanic Cloud, is below it.

Researchers were able to hone in on the location of the gravitational-wave source using data from the LIGO observatories in Livingston, Louisiana and Hanford, Washington. The gravitational waves arrived at Livingston 7 milliseconds before arriving at Hanford. This time delay revealed a particular slice of sky, or ring, from which the signal must have arisen. Further analysis of the varying signal strength at both detectors ruled out portions of the ring, leaving the remaining patch shown on this map. In the future, when additional gravitational-wave detectors are up and running, scientists will be able to pinpoint more precisely the locations and sources of signals.

More about this image
On Sept. 14, 2015, at 5:51 a.m. EDT (09:51 UTC), for the first time, scientists observed ripples in the fabric of spacetime, called gravitational waves, arriving at Earth from a cataclysmic event in the distant universe. This confirmed a major prediction of Albert Einstein's 1915 general theory of relativity and opens an unprecedented new window to the cosmos.

The gravitational waves were detected by both of the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, located in Livingston, Louisiana and Hanford, Washington. The LIGO observatories are funded by the National Science Foundation (NSF), and were conceived, built and are operated by the California Institute of Technology (Caltech) and the Massachusetts Institute of Technology (MIT).

Gravitational waves carry information about their dramatic origins and about the nature of gravity that cannot be obtained from elsewhere. Physicists have concluded that the detected gravitational waves were produced during the final fraction of a second of the merger of two black holes to produce a single, more massive spinning black hole. This collision of two black holes had been predicted but never observed.

Based on the observed signals, LIGO scientists estimate that the black holes for this event were about 29 and 36 times the mass of the sun, and the event took place 1.3 billion years ago. About three times the mass of the sun was converted into gravitational waves in a fraction of a second, with a peak power output about 50 times that of the whole visible universe. By looking at the time of arrival of the signals -- the detector in Livingston recorded the event 7 milliseconds before the detector in Hanford -- scientists can say that the source was located in the Southern Hemisphere.

The new LIGO discovery is the first observation of gravitational waves themselves, made by measuring the tiny disturbances the waves make to space and time as they pass through the Earth.

To learn more about this exciting discovery, see NSF press release 16-015, Gravitational waves detected 100 years after Einstein's prediction. To learn more about LIGO, see the NSF Special Report LIGO #Einstein was right. (Date image taken: Feb. 11, 2016; date originally posted to NSF Multimedia Gallery: March 17, 2016) [Image 4 of 15 related images. See Image 5.]

Credit: LIGO/Axel Mellinger

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