2016-02-11 Gravitational Waves Detected

LIGO opens new window on the universe with observation of gravitational waves from colliding black holes.

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PRESS CONFERENCE & REACTION

VIDEOS & ANIMATIONS

A computer simulation shows the collision of two black holes, a tremendously powerful event detected for the first time ever by the Laser Interferometer Gravitational-Wave Observatory, or LIGO. LIGO detected gravitational waves, or ripples in space and time generated as the black holes spiraled in toward each other, collided, and merged. This simulation shows how the merger would appear to our eyes if we could somehow travel in a spaceship for a closer look. It was created by solving equations from Albert Einstein's general theory of relativity using the LIGO data.

The two merging black holes are each roughly 30 times the mass of the sun, with one slightly larger than the other. The event took place 1.3 billion years ago.

The stars appear warped due to the incredibly strong gravity of the black holes. The black holes warp space and time, and this causes light from the stars to curve around the black holes in a process called gravitational lensing. The ring around the black holes, known as an Einstein ring, arises from the light of all the stars in a small region behind the holes, where gravitational lensing has smeared their images into a ring.

The gravitational waves themselves would not be seen by a human near the black holes and so do not show in this video, with one important exception. The gravitational waves that are traveling outward toward the small region behind the black holes disturb that region's stellar images in the Einstein ring, causing them to slosh around, even long after the collision. The gravitational waves traveling in other directions cause weaker, and shorter-lived sloshing, everywhere outside the ring.

This simulation was created by the multi-university Simulating eXtreme Spacetimes (SXS) project. For more information, visit http://www.black-holes.org.

Credit: Simulating eXtreme Spacetimes (SXS) Project

The Sound of Two Black Holes Colliding (0:12)

Gravitational waves sent out from a pair of colliding black holes have been converted to sound waves, as heard in this animation. On September 14, 2015, LIGO observed gravitational waves from the merger of two black holes, each about 30 times the mass of our sun. The incredibly powerful event, which released 50 times more energy than all the stars in the observable universe, lasted only fractions of a second.

In the first two runs of the animation, the sound-wave frequencies exactly match the frequencies of the gravitational waves. The second two runs of the animation play the sounds again at higher frequencies that better fit the human hearing range. The animation ends by playing the original frequencies again twice.

As the black holes spiral closer and closer in together, the frequency of the gravitational waves increases. Scientists call these sounds "chirps," because some events that generate gravitation waves would sound like a bird's chirp.

Credit: LIGO

Warped Space and Time Around Colliding Black Holes (1:13)

This computer simulation shows the warping of space and time around two colliding black holes observed by LIGO on September 14, 2015. LIGO detected gravitational waves generated by this black hole merger—humanity's first contact with gravitational waves and black-hole collisions. Gravitational waves are ripples in the shape of space and flow of time.

The colored surface is the space of our universe, as viewed from a hypothetical, flat, higher-dimensional universe, in which our own universe is embedded. Our universe looks like a warped two-dimensional sheet because one of its three space dimensions has been removed. Around each black hole, space bends downward in a funnel shape, a warping produced by the black hole's huge mass. Near the black holes, the colors depict the rate at which time flows. In the green regions outside the holes, time flows at its normal rate. In the yellow regions, it is slowed by 20 or 30 percent. In the red regions, time is hugely slowed. Far from the holes, the blue and purple bands depict outgoing gravitational waves, produced by the black holes' orbital movement and collision.

Our universe's space, as seen from the hypothetical higher-dimensional universe, is dragged into motion by the orbital movement of the black holes, and by their gravity and by their spins. This motion of space is depicted by silver arrows, and it causes the plane of the orbit to precess gradually, as seen in the video. The upper left numbers show time, as measured by a hypothetical person near the black holes (but not so near that time is warped). The bottom portion of the movie shows the waveform, or wave shape, of the emitted gravitational waves.

The gravitational waves carry away energy, causing the black holes to spiral inward and collide. The movie switches to slow motion as the collision nears, and is paused at the moment the black holes' surfaces (their "horizons") touch. At the pause, space is enormously distorted. After the pause, again seen in slow motion, the shapes of space and time oscillate briefly but wildly, and then settle down into the quiescent state of a merged black hole. Returning to fast motion, we see the gravitational waves from the collision, propagating out into the universe.

The collision and wild oscillations constitute a "storm" in the fabric of space and time—an enormously powerful but brief storm. During the storm, the power output in gravitational waves is far greater than the luminosity of all the stars in our observable universe put together. In other words, this collision of two black holes, each the size of a large city on Earth, is the most powerful explosion that astronomers have ever seen, aside from our universe's birth in the Big Bang.

This simulation was created by the Simulating eXtreme Spacetimes (SXS) Project (http://www.black-holes.org).

Credit: Simulating eXtreme Spacetimes (SXS) Project

GRAPHICS

Current operating facilities in the global network include the twin LIGO detectors—in Hanford, Washington, and Livingston, Louisiana—and GEO600 in Germany. The Virgo detector in Italy and the Kamioka Gravitational Wave Detector (KAGRA) in Japan are undergoing upgrades and are expected to begin operations in 2016 and 2018, respectively. A sixth observatory is being planned in India. Having more gravitational-wave observatories around the globe helps scientists pin down the locations and sources of gravitational waves coming from space.

Credit: LIGO

Two Black Holes Merge into One

The collision of two black holes—an event detected for the first time ever by the Laser Interferometer Gravitational-Wave Observatory, or LIGO—is seen in this still from a computer simulation. LIGO detected gravitational waves, or ripples in space and time, generated as the black holes merged. The simulation shows what the merger would look like if we could somehow get a closer look. Time has been slowed by a factor of 100. The stars appear warped due to the strong gravity of the black holes.

Credit: SXS

Gravitational Waves, As Einstein Predicted

These plots show the signals of gravitational waves detected by the twin LIGO observatories at Livingston, Louisiana, and Hanford, Washington. The signals came from two merging black holes, each about 30 times the mass of our sun, lying 1.3 billion light-years away.

The top two plots show data received at Livingston and Hanford, along with the predicted shapes for the waveform. These predicted waveforms show what two merging black holes should look like according to the equations of Albert Einstein's general theory of relativity, along with the instrument's ever-present noise. Time is plotted on the X-axis and strain on the Y-axis. Strain represents the fractional amount by which distances are distorted.

As the plots reveal, the LIGO data very closely match Einstein's predictions.

The final plot compares data from both detectors. The Hanford data have been inverted for comparison, due to the differences in orientation of the detectors at the two sites. The data were also shifted to correct for the travel time of the gravitational-wave signals between Livingston and Hanford (the signal first reached Livingston, and then, traveling at the speed of light, reached Hanford seven thousandths of a second later). As the plot demonstrates, both detectors witnessed the same event, confirming the detection.

Credit: LIGO

Where the Gravitational Waves Came From

The approximate location of the source of gravitational waves detected on September 14, 2015, by the twin 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; 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 home 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.

Backdrop Milky Way image is courtesy Axel Mellinger.
Image Credit: LIGO/Axel Mellinger

PHOTOS

Inspecting LIGO's optics for contaminants
Prior to sealing up the chamber and pumping the vacuum system down, a LIGO optics technician inspects one of LIGO's core optics (mirrors) by illuminating its surface with light at a glancing angle. It is critical to LIGO's operation that there is no contamination on any of its optical surfaces.

Credit: Matt Heintze/Caltech/MIT/LIGO Lab

Hanford achieves interferometer lock
On December 12, 2014, LIGO Hanford achieved its first interferometer "lock". "Locking" refers to the times during which infrared light resonates throughout the interferometer under computer control. The photo shows LIGO Hanford scientists and engineers at work in the control room on December 3, 2014.

Credit: Caltech/MIT/LIGO Lab

For a complete library of images, please visit the LIGO observatories image galleries online:

Caltech's Dave Reitze, executive director of the LIGO laboratory, says to a packed audience and online viewers around the world: "Ladies and gentleman, we have detected gravitational waves. We did it!"

Credit: Kathy Svitil/Caltech

(On the right) Kip Thorne, Caltech's Richard P. Feynman Professor of Theoretical Physics, Emeritus. "With this discovery, we're embarking on a marvelous quest: the quest to explore the warped side of the universe."

Credit: Kathy Svitil/Caltech