Media Tip Sheets

Today, the LIGO Livingston detector and VIRGO detector captured another binary neutron star merger

Stefan Ballmer is an associate professor of physics at Syracuse University’s College of Arts and Sciences. Below, he answers four key questions about the LIGO/VIRGO detection, and what it means for the greater world of physics.

Q: What is most significant about these findings?

Ballmer: “What we are really looking forward to is to get a stronger signal from the collision phase of the two neutron stars. That will tell us how nuclear matter behaves under these extreme conditions.

“This event was a little too far away for that. But it gives us a much better handle on the rate of such collisions. The upshot: if we just observe a little longer we will get the strong signal we are hoping for.”

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Q: Can you break down what a binary neutron star merger is?

Ballmer: “A neutron star is an atomic nucleus the size of a city, but with the mass of a sun. We are observing the collision of two of these monsters at about half the speed of light.

“Since neutron stars still are made of matter (unlike black holes), we do expect to be able to see them optically as well, as was the case with GW170817, the first binary neutron star merger observed by LIGO.”

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Q: For someone not familiar with the physics world, why is this exciting?

Ballmer: “On a weekly basis we are now observing some of the most violent events in the universe, literally storms in space and time, shredding the remnants of stars. Black holes and neutron stars are no longer exotic hypothetical objects they once were, but the bread and butter of everyday science.

“This is also why the LIGO and Virgo collaborations now put out alerts as quickly as possible, in the hope that other astronomers can make complementary observations.

“In fact, you can download an app that alerts you within minutes whenever we see something interesting.” Link: https://itunes.apple.com/us/app/gravitational-wave-events/id1441897107

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Q: How does this tie in or connect with (if at all) with the first black hole image that was released just a short while ago?

Ballmer: “Since the latest run (O3) started we have observed 3 black hole mergers, and this neutron star merger. That brings the total observed in all runs to 13 black hole mergers and 2 neutron star mergers.

“It is amazing that what was considered to be impossible just three and a half years ago – and was worth the 2017 Nobel prize – is now happening weekly.”

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Syracuse University </s> 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> 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 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> 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> 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. </s> In yet another historic moment, an international research team, including scientists from India, has announced the third detection of gravitational waves -- ripples in the fabric of space and time which were first predicted by Albert Einstein more than a century ago.

The Laser Interferometer Gravitational-wave Observatory (LIGO) in the US made the detection on January 4 this year, demonstrating that a new window in astronomy has been firmly opened.

Gravitational waves pass through Earth and can be "heard" by the extremely sensitive LIGO detectors.

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

"Our handful of detections so far is revealing an intriguing black hole population we did not know existed until now," said Northwestern University's Vicky Kalogera, a senior astrophysicist with the LIGO Scientific Collaboration (LSC).

The new detection, called GW170104, occurred during the ongoing second observing run of the Advanced LIGO detectors which began on November 30 last year.

The first direct observation of gravitational waves was made in September 2015 during the first observing run.

A second detection was made in December 2015.

The third detection is described in a new paper accepted for publication in the journal Physical Review Letters.

The publication has 40 authors from 11 Indian institutions.

IIT-Madras recently joined the LSC as one of the participating institutes, under the leadership of Dr Chandra Kant Mishra.

The Chennai Mathematical Institute has also been contributing to the activities under the leadership of Dr K.G. Arun.

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The group at IIT-Madras is involved in modelling the gravitational wave sources such as the ones which have been detected by the LIGO detectors so far as well as testing the consistency of the detected gravitational wave signals with the predictions of Einstein's general theory of relativity.

The third and latest detection points to merging black holes that are twice as far away from Earth as the two earlier pairs -- about three billion light-years away.

This time, the two black holes were unequal in size, one significantly lighter than the other. They merged into a black hole whose size is in the middle of the other two merged black hole pairs.

"Now we have three pairs of black holes, each pair ending their death spiral dance over millions or billions of years in some of the most powerful explosions in the universe. In astronomy, we say with three objects of the same type you have a class. We have a population, and we can do analysis," Kalogera added.

The newfound black hole, formed by the pair's 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, which had solar masses of 62 (first detection) and 21 (second detection).

"We have further confirmation of the existence of black holes that are heavier than 20 solar masses, objects we didn't know existed before LIGO detected them," said David Shoemaker of MIT, the newly elected spokesperson for the LSC.

India is also working towards setting up its own LIGO observatory.

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The move received in-principle approval from the cabinet in February last year and has made rapid progress towards the plan to join these exciting scientific observations in 2024.

LIGO-India will greatly enhance the scientific capabilities of the international network of observatories for astronomy, primarily by enabling precise pointing to the location of the gravitational wave events in the sky.

Scientific and engineering teams at IPR Gandhinagar, IUCAA Pune and RRCAT Indore are actively engaged in the pre-construction activities of LIGO-India. </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> An international team of scientists - including 21 researchers from The University of Western Australia - has detected gravitational waves for the third time in history. The first time was in September 2015, then again in December 2015.

Gravitational waves are waves of energy, ripples in the fabric of space-time. The discovery of the first wave proved a prediction by Einstein 100 years ago.

The newfound black hole, formed by the pair's 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, which had solar masses of 62 (first detection) and 21 (second detection).

These collisions produce more power during the instant before the black holes merge, than is radiated as light by all the stars and galaxies in the universe at any given time. The recent detection is the farthest yet, with the black holes located about 3 billion light-years away.

The black holes in the first and second detections are located 1.3 and 1.4 billion light-years away, respectively.

The third and most recent detection, called GW170104, was made on January 4 this year. The latest finding solidifies the case for a new class of black hole pairs, or binary black holes, with masses that are larger than what had been seen before by the Laser Interferometer Gravitational-wave Observatory (LIGO) detectors.

Professor David Blair, from UWA's School of Physics, said the event released more energy in its last few orbits than that of rest of the entire universe.

"Yet when the ripples passed the LIGO detector they made it vibrate by just one attometer, or 0.000000000000000001 metres," Professor Blair said.

Despite this tiny displacement, the scientists were able to demonstrate the black holes exhibited a property known as "spin".

"This is the first time that we have evidence that the black holes may not be aligned, giving us just a tiny hint that pairs of black holes may form in dense stellar clusters," Professor Blair said.

Postdoctoral Fellow Qi Chu, from UWA's School of Physics, is part of a team led by OzGrav Chief Investigator Professor Linqing Wen that is racing to create faster ways to crunch the LIGO data to minimise the time between the gravitational waves hitting earth and an alert being sent out for follow-up observations.

"The LIGO detector lets us feel the gravitational wave, and we are on a mission to see the source of the event by looking through powerful telescopes," Ms Chu said.

An international group of researchers, including the Australian International Gravitational Research Centre, is also investigating how to fine-tune the sensitivity of the gravitational waves detector, leading to improved detection of future gravitational waves and electromagnetic observational, and potentially more exotic sources.

LIGO is funded by the National Science Foundation (NSF), and operated by MIT and Caltech, which conceived and built the project. Financial support for the Advanced LIGO project was led by NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council) making significant commitments and contributions 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, a consortium including 280 additional scientists throughout Europe supported by the Centre National de la Recherche Scientifique (CNRS), the Istituto Nazionale di Fisica Nucleare (INFN), and Nikhef, as well as Virgo's host institution, the European Gravitational Observatory.

The ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) is funded by the Australian Government through the Australian Research Council Centres of Excellence funding scheme. OzGrav is a partnership between Swinburne University (host of OzGrav headquarters), the Australian National University, Monash University, University of Adelaide, University of Melbourne, and University of Western Australia, along with other collaborating organisations in Australia and overseas.
LIGO detects a second neutron star merger using its gravitational wave signal after the first such detection in August 2017.