In February of 2016, scientists at the Laser Interferometer Gravitational-wave Observatory (LIGO) announced the first-ever detection of gravitational waves (GWs). Since then, multiple events have been detected, providing insight into a cosmic phenomena that was predicted over a century ago by Einstein’s Theory of General Relativity.

A little over a year ago, LIGO was taken offline so that upgrades could be made to its instruments, which would allow for detections to take place “weekly or even more often.” After completing the upgrades on April 1st, the observatory went back online and performed as expected, detecting two probable gravitational wave events in the space of two weeks.

LIGO announced the first of the two new GW events on April 8th, which was followed by a second announcement on April 12th. The signals were detected thanks to the three-facility collaboration between LIGO and the Virgo Observatory in Italy, and both are believed to have been the result of a pair of black holes merging.

Thanks to upgrades made to both LIGO and Virgo, this scientific collaboration has been able to increase the sensitivity of its instruments by about 40%. For their third observation run (dubbed O3), the astronomical community also benefited from a new public alert system, where the LIGO team sends out alerts the moment detections are made so that observatories around the world can point their telescopes at the source.

By observing the source in different wavelengths (optical, X-ray, ultraviolet, radio, etc.), scientists hope to learn more about what causes GW events and about the dynamics behind them. For these latest detections, a team of scientists from Penn State University – led by Chad Hanna, an associate professor of physics, astronomy and astrophysics – played a vital role.

As Cody Messick, a graduate student in physics at Penn State and member of the LIGO team, explained:

“Penn State is part of a small team of LIGO scientists that analyze the data in almost real-time. We are constantly comparing the data to hundreds of thousands of different possible gravitational waves and upload any significant candidates to a database as soon as possible. Although there are several different teams all performing similar analyses, the analysis ran by the Penn State team uploaded the candidates that were made public for both of these detections.”

Over the past nine months, Messick has been responsible for ensuring that newly-uploaded GW candidates contain information from all detectors running at the time of detection. This helps astronomers localize signals by narrowing down the predicted area of the sky that the signal is predicted to have come from.

LIGO public alerts also include a sky-map that shows the possible location of the source in the sky, the time of the event, and what kind of event it is believed to be. LIGO has also said that in the future, announcements of candidate events will be followed by more detailed information once they have had a chance to properly vet and study them.

As Ryan Magee, a graduate student in physics at Penn State and member of the LIGO team, put it:

“These are near real-time detections of gravitational waves produced from two probable black holes colliding. We detected the first signal within about 20 seconds of its arrival to earth. We can set up automatic alerts to get phone calls and texts when a significant candidate is identified. I thought I was getting a spam phone call at first!”

So far, astronomers have deduced that GW events can be the result of binary black hole mergers, a merger between a black hole and a neutron star, or a binary neutron star merger. Each of these events produce gravitational waves with very different signals, which allows astronomers to determine the cause.

In this case, the events are believed to be the result of binary black hole mergers, which will be tested with follow-up observations in the coming weeks and months. Surabhi Sachdev, a Eberly Postdoctoral Research Fellow in physics at Penn State and member of the LIGO team, explained the importance of these latest events:

“This is the first LIGO observation that was made public right away in an automated fashion. This is the new LIGO policy starting with this observing run. Events are instantly made public automatically. After human vetting, a confirmation or retraction is issued within hours.”

With the increased sensitivity of their detectors, the LIGO team hopes to not only make more detections, but detect a greater variety of signals. So far, events have been detected that were the result of mergers between two black holes or neutron stars. It is hoped that in the near future, the team might detect a signal produced by the merger of a black hole and a neutron star.

Whatever form the next events take, you can expect that we will be hearing about it! The public can keep track of public alerts at https://gracedb.ligo.org/latest/, or you can download the alert app at Gravitational Wave Events iPhone App. </s> Aerial view of the Virgo site showing the Mode-Cleaner building, the Central building, the three kilometer-long west arm and the beginning of the north arm. The other buildings include offices, workshops, computer rooms and the control room of the interferometer. Credit: The Virgo collaboration/CCO 1.0

In August, detectors on two continents recorded gravitational wave signals from a pair of black holes colliding. This discovery, announced today, is the first observation of gravitational waves by three different detectors, marking a new era of greater insights and improved localization of cosmic events now available through globally networked gravitational-wave observatories.

The collision was observed Aug. 14 at 10:30:43 a.m. Coordinated Universal Time (UTC) using the two National Science Foundation (NSF)-funded Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors located in Livingston, Louisiana, and Hanford, Washington, and the Virgo detector, funded by CNRS and INFN and located near Pisa, Italy.

The detection by the LIGO Scientific Collaboration (LSC) and the Virgo collaboration is the first confirmed gravitational wave signal recorded by the Virgo detector. A paper about the event, a collision designated GW170814, has been accepted for publication in the journal Physical Review Letters.

"Little more than a year and a half ago, NSF announced that its Laser Interferometer Gravitational Wave Observatory had made the first-ever detection of gravitational waves, which resulted from the collision of two black holes in a galaxy a billion light-years away," said NSF Director France Córdova. "Today, we are delighted to announce the first discovery made in partnership between the Virgo gravitational-wave observatory and the LIGO Scientific Collaboration, the first time a gravitational wave detection was observed by these observatories, located thousands of miles apart. This is an exciting milestone in the growing international scientific effort to unlock the extraordinary mysteries of our universe."

LIGO operates two detector sites -- one near Hanford in eastern Washington, and another near Livingston, Louisiana. The Livingston detector site is pictured here. Credit: LIGO Collaboration

The detected gravitational waves—ripples in space and time—were emitted during the final moments of the merger of two black holes, one with a mass about 31 times that of our sun, the other about 25 times the mass of the sun. The event, located about 1.8 billion light-years away resulted in a spinning black hole with about 53 times the mass of our sun—that means about three solar masses were converted into gravitational-wave energy during the coalescence.

"This is just the beginning of observations with the network enabled by Virgo and LIGO working together," says LSC spokesperson David Shoemaker of the Massachusetts Institute of Technology (MIT). "With the next observing run planned for fall 2018, we can expect such detections weekly or even more often."

LIGO has transitioned into a second-generation gravitational-wave detector, known as Advanced LIGO, that consists of two identical interferometers. Beginning operations in September 2015, Advanced LIGO has conducted two observing runs. The second observing run, "O2," began Nov. 30, 2016, and ended Aug. 25, 2017.

The Virgo detector, also now a second-generation detector, joined the O2 run Aug. 1, 2017 at 10 a.m. UTC. The real-time detection Aug. 14 was triggered with data from all three LIGO and Virgo instruments.

View of the LIGO detector in Hanford, Washington. LIGO research is carried out by the LIGO Scientific Collaboration, a group of more than 1,000 scientists from universities around the US and 14 other countries. Credit: LIGO Laboratory

"It is wonderful to see a first gravitational-wave signal in our brand new Advanced Virgo detector only two weeks after it officially started taking data," says Jo van den Brand of Nikhef and Vrije Universiteit Amsterdam, spokesperson of the Virgo collaboration. "That's a great reward after all the work done in the Advanced Virgo project to upgrade the instrument over the past six years."

When an event is detected by a three-detector network, the area in the sky likely to contain the source shrinks significantly, improving distance accuracy. The sky region for GW170814 has a size of only 60 square degrees, more than 10 times smaller than the size using data available from the two LIGO interferometers alone.

"Being able to identify a smaller search region is important, because many compact object mergers—for example those involving neutron stars—are expected to produce broadband electromagnetic emissions in addition to gravitational waves," says Georgia Tech's Laura Cadonati, deputy spokesperson for the LIGO Scientific Collaboration. "This precision pointing information enabled 25 partner facilities to perform follow-up observations based on the LIGO-Virgo detection, but no counterpart was identified—as expected for black holes."

"With this first joint detection by the Advanced LIGO and Virgo detectors, we have taken one step further into the gravitational-wave cosmos," says Caltech's David H. Reitze, executive director of the LIGO Laboratory. "Virgo brings a powerful new capability to detect and better locate gravitational-wave sources, one that will undoubtedly lead to exciting and unanticipated results in the future."

Explore further New gravitational wave data analysis now underway </s> One of LIGO’s gravitational wave detectors Christian Offenberg / Alamy Stock Photo

LIGO is back at it. Having just turned back on after months of upgrades on 1 April, the Laser Interferometer Gravitational-Wave Observatory has already spotted another pair of black holes colliding.

Gravitational waves are ripples in space-time that occur whenever massive objects move, like the wake behind a boat travelling across a lake. LIGO announced the first-ever observations of gravitational waves in 2016 and has now spotted a total of 12 gravitational signatures of pairs of enormous objects smashing together.

Now that the twin detectors in Livingston, Louisiana, and Hanford, Washington, have been upgraded, we expect to see about one set of gravitational waves per week. And just one week after the detectors were turned back on, that expectation is already becoming reality with the detection of gravitational waves from a pair of merging black holes almost 5 billion light years away. LIGO made the find in collaboration with the Virgo gravitational wave observatory in Italy.

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LIGO and Virgo haven’t released any information on the sizes of the two black holes. But based on the strength of the signal from so far away, they are probably relatively large like several of the earlier detections, perhaps around 30 times the mass of the sun, says astronomer Derek Fox at Pennsylvania State University. “Just being big and loud and right at the beginning of the run is exciting,” he says.

Now, these marvels of general relativity have become almost commonplace, so much so that you can sign up to be alerted to each new detection via an iPhone app. The point of the public alerts is to let astronomers around the world know where to point their telescopes for follow-up observations, says Fox.

That will come in handy during this new set of observations, which is expected to last a year or more. “This observing run is supposed to bring a real harvest of black holes and also probably a few neutron stars,” says Fox. “Some of us have been looking forward to this new era for a long time.” </s> On January 4, 2017, at 11:11:58 CET, scientists observed gravitational waves--ripples in the fabric of spacetime--for the third time.

The twin Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors--located in Livingston, Louisiana, and Hanford, Washington--detected the gravitational wave event, named GW170104. The LIGO Scientific Collaboration (LSC) and the Virgo Collaboration published a report describing the discovery and its implications on June 1, 2017 in the journal Physical Review Letters.

Gravitational waves carry information about their origins and about the nature of gravity that cannot otherwise be obtained. Physicists on the LIGO and Virgo teams concluded that, as with LIGO's first two historic detections, the final moments of a black hole merger produced the gravitational waves that LIGO observed on January 4, 2017.

LIGO's first detection, on September 14, 2015, resulted from a merger of two black holes about 36 and 29 times the mass of the sun. In contrast, the black holes that created the second event were relative flyweights, tipping the scales at 14 and eight times the mass of the sun.

The third and most recent detection lies in the middle, resulting from a merger between two black holes, more than 31 and 19 times the mass of the sun, respectively. The merger produced a single, more massive black hole that is slightly less than 49 times the mass of the sun, and transformed the remaining mass into gravitational energy.

"The observation and interpretation of yet another LIGO signal, GW170104, confirms the success of our theoretical program to model binary black holes," said Alessandra Buonanno, a UMD College Park Professor of Physics and LSC principal investigator who also has an appointment as Director at the Max Planck Institute for Gravitational Physics in Potsdam, Germany. Buonanno has led the effort to develop highly accurate models of gravitational waves that black holes would generate in the final process of orbiting and colliding with each other.

"For the third LIGO signal we could gather some evidence that at least one black hole might be rotating in a direction misaligned with the overall orbital motion--a spin configuration favored by some astrophysical formation scenarios of binary black holes" Buonanno added, noting that her team made substantial improvements to their methodology throughout 2016, in between LIGO's observing runs.

The newly detected merger occurred approximately 3 billion years ago, making it more than twice as old (and more than twice as distant) as the first two events, which occurred 1.3 and 1.4 billion years ago, respectively. Based on the arrival time of the signals--the Hanford detector measured the waves 3 milliseconds before the Livingston detector--researchers can roughly determine the position of the source in the sky.

The first detection of gravitational waves, announced on February 11, 2016, was a milestone in physics and astronomy. It confirmed a major prediction of Albert Einstein's 1915 general theory of relativity and marked the beginning of the new field of gravitational wave astronomy.

"The latest detection adds to the diversity of black hole merger events we've been able to observe directly," said Peter Shawhan, an associate professor of physics at UMD and an LSC principal investigator who serves as Data Analysis Committee Chair for the LSC. "We're conducting a census of black holes in binary systems in our universe and we expect to discover other types of signals too. Besides just counting them, we can learn from their properties how they were born and how they evolved."

The researchers also looked for an effect called dispersion, which is known to occur when light waves in a physical medium such as glass travel at different speeds depending on their wavelength. This is how a prism creates a rainbow, for example. Einstein's general theory of relativity forbids dispersion from happening in gravitational waves as they propagate from their source to Earth. LIGO did not find evidence for this effect in GW170104.

"Even for this new event, which is about two times farther away than our first two detections, we could not find any evidence that gravitational waves disperse as they travel in the fabric of space-time," Buonanno said.

"Einstein still seems to have been right about the true nature of gravity," Shawhan added.

The new detection occurred during LIGO's second observing run, which began November 30, 2016, and will continue through August 2017. The LIGO-Virgo team is continuing to search the latest LIGO data for signs of space-time ripples from the far reaches of the cosmos. They are also working on substantial technical upgrades for LIGO's third run, scheduled to begin in late 2018, with help from the nearly completed Virgo detector in Italy collecting data simultaneously.

The research paper, "GW170104: Observation of a 50-Solar-Mass Binary Black Hole Coalescence at Redshift 0.2," by the LIGO Scientific Collaboration and the Virgo Collaboration, was published online June 1, 2017 in the journal Physical Review Letters.

The LIGO Laboratory is funded by the National Science Foundation (NSF), and operated by Caltech and MIT, which conceived and built the Observatory. The NSF led in financial support for the Advanced LIGO project with funding organizations in Germany (MPG), the U.K. (STFC) and Australia (ARC) making significant commitments to the project. More than 1,000 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. LIGO partners with the Virgo Collaboration, which is supported by Centre National de la Recherche Scientifique (CNRS), Istituto Nazionale di Fisica Nucleare (INFN) and Nikhef, as well as Virgo's host institution, the European Gravitational Observatory, a consortium that includes 280 additional scientists throughout Europe. Additional partners are listed at: http://ligo. .

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The College of Computer, Mathematical, and Natural Sciences at the University of Maryland educates more than 7,000 future scientific leaders in its undergraduate and graduate programs each year. The college's 10 departments and more than a dozen interdisciplinary research centers foster scientific discovery with annual sponsored research funding exceeding $150 million. </s> Two massive black holes colliding into each other created ripples in space and time, known as gravitational waves, which have been detected at the furthest distance yet, international physicists said Thursday.

The galactic mash-up which produced the gravitational waves occurred some three billion light-years away, and marks the science world's third observation of this phenomenon.

The finding further bolsters Einstein's 1915 theory of general relativity, and comes two years after these enigmatic ripples were first detected, said the report in the journal Physical Review Letters.

"It is remarkable that humans can put together a story, and test it, for such strange and extreme events that took place billions of years ago and billions of light-years distant from us," said David Shoemaker, spokesman for the Laser Interferometer Gravitational-wave Observatory (LIGO) Scientific Collaboration.

The group includes more than 1,000 international scientists who perform LIGO research together with the European-based Virgo Collaboration.

In all three cases, each of the twin detectors of LIGO detected gravitational waves from the tremendously energetic mergers of black hole pairs.

"These are collisions that produce more power than is radiated as light by all the stars and galaxies in the universe at any given time," said a LIGO statement.

The latest black hole collision, resulting in a detectable "chirp" of a gravitational wave, happened when two black holes merged, forming a new one that is about 49 times the mass of the Sun.

Its size is smack in the middle of the first such black hole merger detected by LIGO, at 62 solar masses, and the second which had 21.

"We have further confirmation of the existence of stellar-mass black holes that are larger than 20 solar masses -- these are objects we didn't know existed before LIGO detected them," said Shoemaker, a senior research scientist at the Massachusetts Institute of Technology (MIT).

The first-ever direct observation of gravitational waves was made in September 2015, and detected an event some 1.3 billion light-years away.

The second came shortly after, in December 2015, and was a distance of 1.4 billion light-years.

The third detection, called GW170104, was made on January 4, 2017.

"With the third confirmed detection of gravitational waves from the collision of two black holes, LIGO is establishing itself as a powerful observatory for revealing the dark side of the universe," says David Reitze of Caltech, executive director of the LIGO Laboratory.

"While LIGO is uniquely suited to observing these types of events, we hope to see other types of astrophysical events soon, such as the violent collision of two neutron stars."

LIGO's observations are carried out by twin detectors -- one in Hanford, Washington, and the other in Livingston, Louisiana.

The observatories, which use laser interferometers to sense the presence of gravitational waves, are operated by Caltech and MIT with funding from the National Science Foundation (NSF).

"It looks like Einstein was right -- even for this new event, which is about two times farther away than our first detection," said Laura Cadonati, an associate professor at the Georgia Institute of Technology.

"We can see no deviation from the predictions of general relativity, and this greater distance helps us to make that statement with more confidence." </s> After more than a year-long hiatus, the Laser Interferometer Gravitational-Wave Observatory (LIGO) is back online and more sensitive than ever to the tiny ripples in spacetime generated when black holes and dead stars collide.

Following numerous upgrades to its lasers, mirrors, and quantum noise filters, LIGO—which consists of twin detectors in Washington and Louisiana—is now about 40 percent more sensitive to gravitational waves compared to its last run. This means that it can scan about twice the volume of space for smash-ups between two black holes or two neutron stars than before.

Working with its European counterpart, VIRGO, LIGO may even be able to detect gravitational waves from predicted, but as yet unseen, black hole-neutron star mergers.

Here, two longtime members of the LIGO group, Robert Byer and Brian Lantz, explain how the moon passing overhead or earthquakes on the far side of the Earth can disrupt LIGO. Byer, a professor at Stanford University, and Lantz, a senior research scientist, also recall how the first detection of a gravitational wave in 2015 was met with widespread skepticism and discuss plans for LIGO’s future. </s> On Jan. 4, an exquisitely sensitive instrument on Earth detected a disturbance that rippled through space and time. Scientists traced the ripple 3 billion light-years away, back to two ancient black holes on a collision course. This marked the third time in about a year that physicists, thanks to the Laser Interferometer Gravitational-wave Observatory, or LIGO, discovered gravitational waves from the violent death spirals of merging black holes.

The first gravitational wave discovery was announced in February 2016 and the second a few months later. The black holes identified in January were slightly smaller than those in the first detection, but they were much farther away, according to David Shoemaker, a research scientist at the Massachusetts Institute of Technology and spokesman for the LIGO Scientific Collaboration, an international group involving more than a thousand researchers. They reported the details of the new binary black hole system that generated the wave Thursday in the journal Physical Review Letters.

“Gravitational waves are distortions in the metric of space that we live in,” Michael Landry, a LIGO physicist at California Institute of Technology, said during a news conference Wednesday. He used a metaphor of a painting's canvas to describe distorted space. If you grip the top and bottom of the canvas and pull, the picture warps, expanding on one axis while contracting on the other.

Two L-shaped LIGO detectors, one in Washington state and the other in Louisiana, check for these distortions. They shoot synchronized laser beams down perpendicular vacuum tubes, each 2½ miles long. As a gravitational wave passes by, one arm of the L will shrink or expand, throwing the beams out of alignment. The Massachusetts Institute of Technology and California Institute of Technology spearhead the project, with support from the National Science Foundation and scientific agencies from a host of other countries.

“This is exactly what we hoped for from NSF's investment in LIGO: taking us deeper into time and space in ways we couldn't do before the detection of gravitational waves,” NSF director France Córdova said in a statement.

The signal in January failed to set off the usual automated alarm — the LIGO scientists had just restarted the detector, after a short winter break, and hadn't yet properly calibrated the trigger setting at the Washington site. A researcher in Germany, who happened to be poring over the LIGO data, first spotted the wave. (The wave would have been caught eventually, the LIGO team said; in a worst-case scenario there's an offline backup to review.)

The scientists named it GW170104. The wave hit Washington about 3 milliseconds before Louisiana. Given the data captured, the LIGO team calculated that the chance an event like this would be a false alarm would occur once every 70,000 years.

“The key thing to take away is we’re looking for novelty,” Shoemaker said during Wednesday's briefing. On these terms, the new black holes complied, at least a little bit.

Both of these black holes were much more massive than our sun. One was roughly 30 times solar mass, and the other 20 times the sun's mass, putting these black holes in the intermediate range between the first detection (two larger black holes) and second (two smaller black holes).

During this hole-on-hole merger, the equivalent of two solar masses were converted into gravitational waves. “These are the most powerful astronomical events witnessed by human beings,” Landry said.

The new detection also offered hints about the ways black holes spin with respect to their orbits. Georgia Tech astrophysicist Laura Cadonati on Wednesday likened the spinning black holes to a pair of tornadoes that dance around each other. Black holes can spin counterclockwise and clockwise, like tornadoes, but can also tilt at angles tornadoes could never achieve.

“We opened a new window into the universe,” Cadonati said. “Before our discoveries we didn't even know for sure that these black holes existed.”

It is possible that one of the black holes had a misaligned spin, which is to say that it was not spinning in the same direction as its overall spiral orbit. “We have an indication that at least one of the two spins is not aligned with the orbital angular momentum,” said B.S. Sathyaprakash, a cosmologist at Pennsylvania State University, during Wednesday's conference.

If the two black holes are not spinning in the same way, that hints at the way they met. Broadly speaking, there are two ways that binary black hole systems form: They began as an isolated pair of stars (think the dual Tatooine sunset in “Star Wars”) that collapsed, or the black holes collapsed independently in a dense star cluster. Cadonati said “this finding lightly favors the theory” of a cluster of stars.

And once again, Albert Einstein's General Theory of Relativity held up. Einstein's theory indicates that gravitational waves do not disperse through a physical medium, unlike light through a prism.

“Even for this new event, which is about two times farther away than our first two detections, we could not find any evidence that gravitational waves disperse as they travel in the fabric of space-time,” Alessandra Buonanno, a University of Maryland physics professor and LIGO collaborator, said in a statement.

The LIGO team continues to increase the detectors' sensitivity. In Louisiana, workers recently entered the vacuum envelope, clad in sterile bunny suits, to patch up areas where light could scatter in the tubes, cutting down on noise at low frequencies. In Washington, the observatory beefed up its laser to reduce high-frequency noise. With every improvement in clarity, LIGO can push its reach deeper into space.

The two teams will swap notes to improve their systems' range for the next run, scheduled to start in 2018. Italy's Virgo detector, too, is close to completion, which will join in LIGO's hunt for gravitational waves. It is possible, members of the LIGO team said during Wednesday's conference, that future discoveries could include merging neutron stars — collisions between the dense remnants of spent stars, the size of a city with the mass of a sun.

A brief history of gravity, gravitational waves and LIGO

A year later, scientists keep listening to gravitational waves, the soundtrack of the cosmos

For the second time ever, scientists detected gravitational waves from colliding black holes </s> Gravitational waves, ripples through the fabric of space-time predicted by Albert Einstein a century ago, have been detected for a third time.

Scientists first detected the shudders in space-time last year and the discovery was hailed the 'biggest scientific breakthrough of the century'.

Now, for the third time, researchers have detected the warping of space-time caused by a collision of two black holes colliding three billion light-years away - providing a new window on our universe.

Scientists view the the universe as being made up of a 'fabric of space-time'. This corresponds to Einstein's General Theory of Relativity, published in 1916. Objects in the universe bend this fabric, and more massive objects bend it more. Gravitational waves are considered ripples in this fabric. They can be produced, for instance, when black holes orbit each other or by the merging of galaxies. Gravitational waves are also thought to have been produced during the Big Bang. If found, they would not only confirm the Big Bang theory but also offer insights into fundamental physics. For instance, they could shed light on the idea that, at one point, most or all of the forces of nature were combined into a single force. In March 2014, a team operating the Bicep2 telescope, based near the South Pole, believed they had found gravitational waves, but their results were proven to be inaccurate.

The detection was made by the Ligo (Laser Interferometer Gravitational-Wave Observatory) Scientific Collaboration (LSC) on January 4, 2017.

As was the case with the first two detections, the waves were generated when two black holes collided to form a larger black hole.

The newfound black hole, formed by the merger, has a mass about 49 times that of our sun.

This fills in a gap between the masses of the two merged black holes detected previously by Ligo, with solar masses of 62 (first detection) and 21 (second detection).

'We have further confirmation of the existence of stellar-mass black holes that are larger than 20 solar masses -these are objects we didn't know existed before Ligo detected them,' said Dr David Shoemaker, a scientist at the Massachusetts Institute of Technology and the spokesperson for the Ligo scientific Collaboration.

'It is remarkable that humans can put together a story, and test it, for such strange and extreme events that took place billions of years ago and billions of light-years distant from us.

'The entire Ligo and Virgo scientific collaborations worked to put all these pieces together.'

In all three cases, each of the twin detectors of LIGO detected gravitational waves from the tremendously energetic mergers of black hole pairs.

These are collisions that produce more power than is radiated as light by all the stars and galaxies in the universe at any given time.

The recent detection appears to be the farthest yet, with the black holes located about 3 billion light-years away.

Scientists said gravitational waves open a 'new door' for observing the universe and gaining knowledge about enigmatic objects like black holes and neutron stars.

Understanding such astronomical phenomena could be useful in helping us decipher how the universe first came to be.

'This [discovery is taking us deeper into time and space in ways we couldn’t do before the detection of gravitational waves,' said France Córdova, director of the National Science Foundation.

'In this case, we’re exploring approximately three billion light-years away.

'Ligo continues to make remarkable discoveries, transitioning from experiment to gravitational wave observatory.

'More importantly each detection has offered much more than just a sighting.

'Slowly, we are collecting data that unveil the origin and characteristics of these objects, further informing our understanding of the universe.'

WHAT IS THE THEORY OF RELATIVITY? Gravitational waves were predicted under Albert Einstein's (pictured) General Theory of Relativity in 1916 In 1905, Albert Einstein determined that the laws of physics are the same for all non-accelerating observers, and that the speed of light in a vacuum was independent of the motion of all observers - known as the theory of special relativity. This groundbreaking work introduced a new framework for all of physics, and proposed new concepts of space and time. He then spent 10 years trying to include acceleration in the theory, finally publishing his theory of general relativity in 1915. This determined that massive objects cause a distortion in space-time, which is felt as gravity. At its simplest, it can be thought of as a giant rubber sheet with a bowling ball in the centre. As the ball warps the sheet, a planet bends the fabric of space-time, creating the force that we feel as gravity. Any object that comes near to the body falls towards it because of the effect. Einstein predicted that if two massive bodies came together it would create such a huge ripple in space time that it should be detectable on Earth. It was most recently demonstrated in the hit film film Interstellar. In a segment that saw the crew visit a planet which fell within the gravitational grasp of a huge black hole, the event caused time to slow down massively. Crew members on the planet barely aged while those on the ship were decades older on their return. The theory was most recently demonstrated in the hit film film Interstellar, in a segment that saw the crew visit a planet which fell within the gravitational grasp of a huge black hole, causing time to slow down massively, so crew members on the planet barely aged while those on the ship were decades older on their return

'We know this is just the beginning. This ‘window on the universe’ will continue to expand.

'We will watch eagerly as hundreds of researchers from around the world enhance this observatory to illuminate the physics of merging black holes, neutron stars and other astronomical phenomena.'

The newest observation also provides clues about the directions in which the black holes are spinning.

As pairs of black holes spiral around each other, they also spin on their own axes, much like a pair of ice skaters spinning individually while also circling around each other.

Sometimes black holes spin in the same overall orbital direction as the pair is moving, this is known as aligned spins, and sometimes they spin in the opposite direction of the orbital motion.

And black holes can also be tilted away from the orbital plane.

The new Ligo data implies that at least one of the black holes may have been non-aligned compared to the overall orbital motion.

More observations with LIGO are needed to say anything definitive about the spins of binary black holes, but these early data offer clues about how these pairs may form.

'This is the first time that we have evidence that the black holes may not be aligned, giving us just a tiny hint that binary black holes may form in dense stellar clusters,' said Bangalore Sathyaprakash of Cardiff University.

There are two primary theories to explain how binary pairs of black holes can be formed.

The first model proposes that the black holes are born together: they form when each star in a pair of stars explodes, and then, because the original stars were spinning in alignment, the black holes likely remain aligned.

In the other model, the black holes come together later in life within crowded stellar clusters.

The black holes pair up after they sink to the center of a star cluster.

In this scenario, the black holes can spin in any direction relative to their orbital motion.

Because Ligo sees some evidence that the newly discovered black holes are non-aligned, the data favours this dense stellar cluster theory.

'We're starting to gather real statistics on binary black hole systems,' said Keita Kawabe, who is based at the Ligo Hanford Observatory.

'That's interesting because some models of black hole binary formation are somewhat favoured over the others even now and, in the future, we can further narrow this down.'

The study also once again puts Albert Einstein's theories to the test.

For example, the researchers looked for an effect called dispersion, which occurs when light waves in a physical medium such as glass travel at different speeds depending on their wavelength; this is how a prism creates a rainbow.

Einstein's general theory of relativity forbids dispersion from happening in gravitational waves as they propagate from their source to Earth.

And Ligo did not find evidence for this effect.

'It looks like Einstein was right - even for this new event, which is about two times farther away than our first detection,' said Laura Cadonati of Georgia Tech University.

'We can see no deviation from the predictions of general relativity, and this greater distance helps us to make that statement with more confidence.'

The team is continuing to search the latest Ligo data for signs of space-time ripples from the far reaches of the cosmos.

They are also working on technical upgrades for Ligo's next run, scheduled to begin in late 2018, during which the detectors' sensitivity will be improved.

At a press conference, the researchers spoke of their ambition to use Ligo to detect neutron stars.

Neutron stars are created when giant stars die in supernovas and their cores collapse, with the protons and electrons essentially melting into each other to form neutrons.

Researchers hope that improving the sensitivity of Ligo's instruments will help them to finally pinpoint signs of a neutron star, which could come as soon as 'this run or the next'.

They added a lack of understanding about how often neutron stars form could be holding them back from making a momentous discovery.

'With the third confirmed detection of gravitational waves from the collision of two black holes, Ligo is establishing itself as a powerful observatory for revealing the dark side of the universe,' said David Reitze of Caltech, executive director of the Ligo Laboratory.

'While Ligo is uniquely suited to observing these types of events, we hope to see other types of astrophysical events soon, such as the violent collision of two neutron stars.'

HOW DOES THIS HELP US UNDERSTAND THE UNIVERSE? Scientists said gravitational waves open a door for a new way to observe the universe and gain knowledge about enigmatic objects like black holes and neutron stars. By studying gravitational waves they also hope to gain insight into the nature of the very early universe, which has remained mysterious. Everything we know about the cosmos stems from electromagnetic waves such as radio waves, visible light, infrared light, X-rays and gamma rays. But because such waves encounter interference as they travel across the universe, they can tell only part of the story. Gravitational waves experience no such barriers, meaning they can offer a wealth of additional information. Black holes, for example, do not emit light, radio waves and the like, but can be studied via gravitational waves. Being able to detect gravitational waves will help astronomers probe the 'dark Universe'. This is the name given to the large part of the cosmos that is invisible to the light telescopes. They will be able to look deeper into the universe, which means we could better understand the history of the customer. As as result, researchers will be able to investigate black holes and neutron stars. The discovery will also help scientists confirm whether gravitational waves really do travel at the speed of light, as predicted. It will help scientists understand how fast the universe is expanding and what exactly makes stars explode. 'LIGO is just in the beginning with gravitational waves. Over the next decade or two we will have four gravitational windows open looking at the universe,' sad Kip Thorne, Feynman Professor of Theoretical Physics at Caltech.' </s> For the third time, scientists have detected a spacetime rumble caused by a violent collision of two black holes. The Laser Interferometer Gravitational-wave Observatory (LIGO) made the detection, determining that the two black holes merged to create one large black hole in a galaxy about 3 billion light-years away.

"We have observed – on the 4th of January, 2017 – another massive black hole-black hole binary coalescence; the in-spiral and merging of black holes 20 and 30 times the mass of our sun," Dave Shoemaker, a senior research scientist who works at Massachusetts Institute of Technology (MIT) and the spokesperson for the LIGO Scientific Collaboration, told reporters during a special news briefing on Wednesday (May 31).

This gargantuan black hole smashup created an even more massive spinning black hole, approximately 49 times the mass of our sun. In an instant, the equivalent mass twice that of our sun was converted directly into gravitational waves — briefly producing more energy than all the energy that is radiated as light by all the galaxies in the universe at any moment, LIGO scientists say.

After many years of planning, development and construction, LIGO took its first observations in 2002. However, it wasn't until Sept. 14, 2015, that the first historic detection of gravitational waves — an event called "GW150914" — was made. That happened after LIGO underwent upgrades (known as Advanced LIGO) to boost its sensitivity. Then, a second detection ("GW151226") followed a few months later in December, confirming that the first discovery was no fluke.

Now, the LIGO Scientific Collaboration — which consists of over a thousand scientists around the world — has confirmed the third gravitational wave detection ("GW170104"), meaning we're at the cusp of a completely new kind of astronomy.

All the gravitational waves detected so far have been created by the collision of stellar-mass black holes of varied sizes. These are black holes that are a few to a few dozen times the mass of our sun that were likely formed by the death of very massive stars after they'd run out of fuel and exploded as supernovas billions of years ago. Advanced LIGO has reached a crossroads in our gravitational wave search, finally reaching a sensitivity that can detect when very distant black holes collide, creating faint gravitational waves that we now know fill our universe.

The 2015 events were caused by mergers creating black holes 62 and 21 solar masses in galaxies 1.3 and 1.4 billion light-years away, respectively. (Note: As gravitational waves travel at the speed of light these mergers happened 1.3 and 1.4 billion years ago.) This latest detection originated from a merger creating a black hole of 49 solar masses (another "heavy" black hole like the first one), but the merger happened over twice as far away than previous events.

"What this means is that we now have a second candidate in the "heavy" black hole category," says Bangalore Sathyaprakash, of Penn State and Cardiff University and a member of the LIGO Scientific Collaboration.

This is important as, before LIGO made its first detection (a 62 solar mass black hole) and its most recent one (a 49 solar mass black hole), there was no observational evidence that these large black holes even existed. This is an incredible early discovery. Scientists have revealed a brand-new type of large black hole in only three detections.

Things are about to get even more exciting as LIGO undergoes more planned upgrades and other observatories join the hunt for gravitational waves.

"We should expect to see one binary merger event per day once LIGO's designed sensitivity is reached," says Sathyaprakash.

When gravitational waves are detected the conditions of the colliding black holes at the time of the merger can be studied.

"In our analysis, we cannot measure the spins of the individual black holes very well, but we can tell if the black holes are generally spinning in the same direction as the orbital motion," says astrophysicist Laura Cadonati, LIGO Scientific Collaboration deputy spokesperson from Georgia Tech.

But an idea of the individual black hole's spin relative to one another can be figured out by studying the "fingerprint" of the gravitational wave signal, says Cadonati.

Theoretical models of merging black holes indicate that if the two black holes' spins are not aligned, the merging event will happen faster than if the spins are aligned. Also, additional wobbles in the signal are predicted as two spin-aligned black holes get close and begin to merge.

Spin-aligned black holes were likely sibling stars. Both would have been born from massive stars that evolved in close proximity in ancient star factories as a binary pair, eventually dying as supernovas.

But in this most recent event, the merging occurred relatively quickly and no additional oscillations were observed, meaning the two black holes were likely not spin-aligned and probably didn't form together. This gives a clue to their origin: Rather than being formed from sibling binary stars, they were strangers and evolved independently, drifting toward one another in the center of a dense stellar cluster where they eventually merged.

"This has implications for astrophysics ... while we cannot say with certainty, this finding likely favors the theory that these two black holes formed separately in a dense stellar cluster, sank to the core of the cluster and then paired up, rather than being formed together from the collapse of two already paired stars," adds Cadonati.

As black holes are gravitational monsters, they're governed by Einstein's general relativity, so by studying the gravitational waves they produce when they collide, scientists also can study the waves for an effect known as "dispersion." For example, when light travels through a prism, the different wavelengths will travel at different speeds through the glass. This causes dispersion in the beam of light — this is the mechanism that creates a rainbow.

General relativity forbids dispersion from happening to gravitational waves, however. This latest signal traveled across a record 3 billion light-years of spacetime to reach Earth, and LIGO didn't detect any dispersion effects.

"It looks like Einstein was right – even for this new event, which is about two times farther away than our first detection," says Cadonati in a statement. "We can see no deviation from the predictions of general relativity, and this greater distance helps us to make that statement with more confidence."

A New Window to the 'Dark Universe'

Einstein's famous theory of general relativity predicts the existence of gravitational waves, but it's taken humanity over a century to develop the technological know-how to build a detector sensitive enough to perceive them. When an energetic event occurs (like a black hole merger or neutron star collision), spacetime becomes violently disturbed and energy is carried away from the event in the form of gravitational waves — like ripples traveling across the water's surface after dropping a pebble in a pond.

But to detect these waves, astronomers need to build an observatory that can detect incredibly minuscule wobbles in the fabric of spacetime as these waves travel through our planet. Gravitational waves are not part of the electromagnetic spectrum; they cannot be detected by ordinary telescopes that are only sensitive to light.

To open the window to this "dark universe," physicists build gravitational wave detectors like LIGO that reflect incredibly precise lasers along 2.5 mile-long (4 kilometer-long) "L"-shaped tunnels. These tunnels are shielded from external vibrations caused by wind, traffic, tectonic activity and other terrestrial interference. Through a method known as laser interferometry, the distance between the reflecting mirrors inside the tunnel can be measured to a very high precision. Should a gravitational wave travel through our planet, a tiny change in distance may be recorded by the interferometer – this represents the minute squeezing and stretching of spacetime that occurs as gravitational waves propagate.

It's as if physicists have created a virtual tripwire that notifies us when an invisible gravitational wave intruder rumbles local spacetime.

One detector isn't enough to confirm a gravitational wave event, however. In the case of LIGO, one detector is located in Hanford, Washington, and another is located in Livingston, Louisiana — separated by 1,865 miles (3,002 kilometers). Only when the same event is detected by both locations can scientists confirm a gravitational wave signal. Two detectors can even determine a rough direction as to where the wave was traveling from, but if more detectors are added to the network, astronomers hope to eventually pinpoint, with increasing precision, where they originate.

More gravitational wave observatories are planned, and the European Virgo detector, located near Pisa, Italy, is currently undergoing commissioning. Once online, Virgo will be used in conjunction with LIGO to boost observational power of gravitational waves and allow better localization of the cosmic events causing the signals.

Now that the existence of gravitational waves has been confirmed, and astronomers are detecting more black hole mergers, we are entering a new era for astronomy. This is gravitational wave astronomy, where the dark universe will finally be revealed.
LIGO and Virgo detect a gravitational wave from a galaxy 6 billion light-years away in the direction of Cassiopeia, with further details being released on April 10.