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LIGO, VIRGO, KAGRA

VIRGO, LIGO and KAGRA sign agreement to begin joint observation

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LIGO, VIRGO, KAGRA. LIGO, VIRGO, KAGRA.

The world's three principal gravitational-wave detectors - LIGO in the US, VIRGO* in Italy, and now KAGRA in Japan - have today, the 4th of October, 2019, signed a memorandum of agreement (MoA) that covers scientific collaboration. The agreement includes the joint observation of gravitational waves and the sharing of data over the coming years, while it also foresees the expansion of the collaboration through the welcoming of new partners in the future.

"With KAGRA joining, gravitational-wave science will become a global collaborative effort. The Virgo Collaboration looks forward to learning from the new and innovative approach of using an underground and cryogenic interferometer", says Jo van den Brand, Virgo Collaboration Spokesperson.

KAGRA is a gravitational wave observatory developed in Kamioka, Japan under the leadership of the University of Tokyo Institute for Cosmic Ray Research (ICRR). Construction started in 2010 and the highly-sensitive instrument is now nearing readiness.

In December of this year, KAGRA is expected to join the third observing run, called O3, which began on the 1st of April, 2019, and already involves the VIRGO detector and the two LIGO detectors.

The addition of a fourth detector to the global network of gravitational-wave interferometers will help to improve the localisation of gravitational-wave sources, further assisting follow-up astronomical observations and the process of understanding the characteristics of the signals.

The main distinguishing feature of KAGRA, with respect to VIRGO and LIGO, is the fact that the mirrors are operated at cryogenic temperatures, in order to reduce thermal noise. The detector is installed underground in the Kamioka mine, which helps in the overcoming of seismic and wind noise.

The cryogenics and underground-operation technologies are a significant development in the gravitational-wave field, as they are also being studied for the next-generation gravitational-wave detectors, such as the European Einstein Telescope.

* VIRGO denotes the Virgo Collaboration and the European Gravitational Observatory (EGO) Consortium.

Image: LIGO, VIRGO & KAGRA.

Posted: 04/10/2019
Scientists fine-tuning the Advanced Virgo laser source.

O3 - The story so far

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Scientists fine-tuning the Advanced Virgo laser source. Scientists fine-tuning the Advanced Virgo laser source.

Advanced Virgo and the two Advanced LIGO detectors have been taking science data continuously since the 1st of April, 2019, when they began their third observation period, named O3. Together, they form the most sensitive global gravitational-wave observatory to date.

During the past six months, the network has operated with all three of the interferometers active concurrently for 44% of the time. Candidate signals have been identified from as far as 17 billion light years away, as was the case with the candidate event of the 6th of July, 2019 (more information is available here).

O3 has proven very rich in terms of alerts. A total of 31 candidate events have been recorded so far, and the LIGO-Virgo Collaboration has issued several public alerts, which are freely accessible at the Gravitational Wave Candidate Event Database. The alerts facilitate follow-up observations by other telescopes (e.g. electromagnetic and neutrino) and enhance the extraordinary potential of multi-messenger observations, pioneered with the GW170817 event.

During the first and second observation runs - O1 and O2 - ten mergers of binary black holes and one merger of a binary neutron star were identified by the LIGO-Virgo Collaboration (more information here). Since the beginning of O3, the LIGO-Virgo Collaboration has identified approximately one binary merger candidate a week. Preliminary results suggest that the majority are mergers of binary black holes. Detailed analysis is ongoing to understand the properties of all the candidates.

"There have been so many triggers!", says Giuseppe Greco - post-doctoral researcher at the University of Urbino and collaborator at the Istituto Nazionale di Fisica Nucleare (INFN) in Italy - enthusiastically. "It was really exciting to issue so many candidate events. They triggered an extraordinary effort by scientists from all over the world".

"After the alerts are sent, work continues to fully assess whether they are true gravitational-wave detections and to extract all available physics information from the data. The quest for the discovery of a new type of source is extremely motivating", says Marie-Anne Bizouard, CNRS researcher at the Observatoire Côte d’Azur, in France, and Burst Source Group co-chair. "Compact binary system mergers are not the only gravitational-wave source the data analysis groups are working on, day and night, either."

For more information, please click here.

Nicolas Arnaud, a CNRS researcher, currently seconded to the European Gravitational Observatory (EGO), also points out that, "Candidate gravitational-wave events keep the Detector Characterization Group permanently on the look-out. Alerts can pop up at any time, including nights and weekends. Each time Virgo is part of such a trigger, we need to quickly assess the quality of our data. This is one of the inputs required to decide whether the alert will go public or should be retracted. Shifters on duty for a week use tailored automated software and growing expertise to vet the events."

During O3, the interferometers have been left almost undisturbed, in order to maximise the amount of data collected. For Advanced Virgo, the only interruptions have been to allow for weekly maintenance and calibration and sum to an average of around 20 hours per week.

The Virgo and LIGO Scientific Collaborations have, however, agreed to pause O3 for a month, as of the 1st of October. For Advanced Virgo, the break will be used to improve the performance achieved during the O3 run, both in terms of sensitivity to gravitational-waves and duty cycle - the extent to which the interferometers are taking useful science data. O3 will then restart on the 1st of November and will run until the 30th of April, 2020.

"After six months of continuous data-taking, the interferometer needs a check-up", says Matteo Tacca, researcher at Nikhef in The Netherlands and the Virgo Commissioning Coordinator. "Acquiring data for such a long period is not only exciting for gravitational-wave searches, but it is also helpful from the instrumental point of view.

"We can analyse the data that have been produced by the instrument while it was undisturbed, in order to better understand its behaviour. We already have some useful indications for further studies, which may help to improve the instrument. During this break, we will make some hardware upgrades to fix a few issues we have found relating to the stability of the machine. We will also have the opportunity to hunt for some technical noise sources that impact upon the detector sensitivity."

When the O3 pause concludes at the start of November, Advanced Virgo and LIGO should be even better placed to continuously acquire useful science data for another 6 months.

Image: Scientists fine-tuning the Advanced Virgo laser source.

Image credit: EGO/Virgo Collaboration/Gosselin

Posted: 30/09/2019
First month of O3

LIGO-Virgo achievements after the first month of O3

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First month of O3 First month of O3

The first month of the new LIGO-Virgo survey for gravitational waves (GWs) has already rewarded scientists with a rich pool of observations; as well as plenty of work in terms of their interpretation. O3, as the observation run is called, started on the 1st of April and is planned to last for 12 months. Improvements achieved in the sensitivity of the detectors and the fact that the three LIGO-Virgo instruments have been operating simultaneously since day one, are now enabling unprecedented opportunities. In addition, for the first time, LIGO and Virgo are providing public alerts. These are delivered shortly after the detection of credible transient gravitational waves candidates. This strategy aims to facilitate follow-up observations by other telescopes and enhance the extraordinary potential of multi-messenger observations.

"I couldn't have dreamed of a better moment to be on shift!", says Olivier Minazzoli, researcher at Centre Scientifique de Monaco, currently collaborating with the ARTEMIS laboratory in Nice, France, and who has been on shift for the characterisation of the Virgo detector during the past week. "I was expecting to see one binary black hole candidate, at best, certainly not two binary neutron star candidates, and even less the potential first neutron star-black hole candidate ever!".

Five LIGO-Virgo public alerts have been issued since the 1st of April, and they can be freely accessed by visiting the Gravitational Wave Candidate Event Database. Three are classified as candidate mergers of Binary Black Hole (BBH) systems. Full assessment requires more analysis, which is already ongoing. If confirmed, these candidates would add to the catalogue of 10 BBH mergers, detected by LIGO-Virgo in previous runs, and would help to improve our understanding of the formation processes of these extreme compact objects and on the nature of gravity, space and time.

Two more events require deeper investigations by the LIGO-Virgo teams, as well by a larger scientific community. They point to coalescences of binary systems involving at least one Neutron Star (NS), the densest form of matter of which we have proof.

For more information, please click here.

On the 25th of April, at about 08:18 (UTC) one likely merger of a Binary Neutron Star (BNS) system was observed (called S190425z - more information is available at this link). This follows the famous GW170817, the first BNS, which was detected two years ago and which gave birth to multi-messenger astronomy using GWs. The quest for possible associated sources in the electromagnetic spectrum, counterparts of S190425z, is still ongoing. This challenge is much harder than it was for GW170817, as this time the source is four times more distant and the sky localisation provided by LIGO-Virgo is much more uncertain. In fact, S190425z occurred while only two detectors were operating: LIGO-Livingston and Virgo.

The other candidate signal involving a NS (named S190426c - more information is available at this link) occurred on the 26th of April at about 15:22 (UTC). All three of the LIGO-Virgo detectors were observing, but, due to the signal being fainter, there is still some remaining probability that it may not be a genuine astrophysical signal. S190426c is an extremely interesting signal, because its morphology hints that it may have been emitted by a mixed system of a NS merging into a more massive BH. If this is confirmed, it will be another unprecedented discovery. The investigation to understand S190426c will require more time and involve exciting work by the LIGO-Virgo teams.

"I am especially excited", says Tanja Hinderer, postdoc at the University of Amsterdam (NL), "to use GWs and multi-messenger observations to learn about the nature of matter in Neutron Stars at the highest densities, which would cause a teaspoon of NS material to weigh as much as a billion tonnes. The GWs encode the properties of the merging objects, while the eventual electromagnetic/neutrino counterparts probe the merger remnant. Having information from multiple messengers is key to understanding these extreme phenomena. The public alerts are making the hunt for multi-messenger counterparts highly exciting, and I am very curious about the diverse signatures associated with different BNS and NS-BH events in O3 and what insights we can gain from them."

"The latest LIGO-Virgo observing run is proving to be the most exciting one so far," says David Reitze, executive director of LIGO at Caltech. "We’re already seeing hints of the first observation of a black hole swallowing a neutron star. If it holds up, this would be a trifecta for LIGO and Virgo. But we’ve learned that claims of detections require a tremendous amount of painstaking work—checking and rechecking — so we'll have to see where the data takes us."

"Dealing with three heterogeneous detectors is challenging work", says Florian Aubin, PhD student at the University Savoie Mont Blanc, France. "But it is also a great opportunity to identify the sky position of the source and search for electromagnetic / neutrino counterparts. I am very excited for the coming run. These two NS merger candidates and the other three BBH merger candidates, in less than a month, promise a full year of interesting discoveries. It is really rewarding for me to be here, after two years of tough work."

Before starting O3, all detectors in the network, namely the two Advanced LIGO interferometers at Livingston and Hanford in the USA, and the Advanced Virgo interferometer at Cascina (Pisa, Italy), undertook an intense period of improvements. Advanced Virgo almost doubled its sensitivity with respect to the second observing run, O2, which ended in 2017.

"It has been 18 months of hard work since September 2017 to improve the Advanced Virgo sensitivity and its robustness against external disturbances", says Irene Fiori, physicist at the European Gravitational Observatory (EGO, Italy) and in charge of Virgo Environmental Noise Studies. "It has been a great collaborative work with experts in many fields: high quality laser beams, super fine alignments of optics, seismic isolation, compensation of thermal defects, and more. Even the production of squeezed light!"

On average, Advanced Virgo can now reliably observe the merger of a BNS at a distance from the Earth of approximately 160 million light years, and the merger of a BBH system at a distance of about 2 billion light years (for BH masses equal to 30 solar masses). Currently, Advanced Virgo is the detector in the network with the highest percentage of time spent observing the Universe. 90% of its operational time has been spent in observation mode; a remarkable success, which has mainly been limited only by maintenance work, which is planned in coordination with LIGO in order to optimise the network performance, and by occasional strong environmental disturbances. This very high duty-cycle reflects the accuracy with which Advanced Virgo is controlled and the stability of the instrumental noise. It also makes Virgo more likely to contribute to GW detections that are still to come during O3.

"In the Virgo Control room", Fiori adds, "we shared hard work, long scientific discussions and strong feelings. On a daily basis, you could tell from people's moods whether Virgo was progressing or stuck. There was great joy when, on the 1st of April, we inaugurated, along with LIGO, the start of the O3 run, with double the sensitivity with respect to 2017. ‘We did it!’, was a common cry. Now, each time we harvest a new GW signal there is renewed satisfaction."

The very high duty cycle of Advanced Virgo, combined with its distance from and different orientation with respect to, the two Advanced LIGO interferometers, increases the capabilities of the detector network to localise GW sources in the sky and to fully understand the characteristics of the GW signals. Indeed a good sky localisation is the key factor that can lead to a successful campaign of electromagnetic observations and the wealth of scientific results that can follow.

Many detections are expected as Advanced LIGO and Advanced Virgo continue observations during O3, which is scheduled to last one year: more mergers of binaries of Black Holes and Neutron Stars, but hopefully, also new GW signals emitted by other types of astrophysical systems. Both the live data analysis methods that scan the data as soon as they are acquired, and the offline analyses that process big chunks of data using all the information available at the time, will continue the search for GW signals, expected or not.

Image: Simulation of a binary neutron star merger. From top left, clockwise: the two neutron stars (drawn in white) spiral around each other, come into contact, and merge into one heavy neutron star. Some of the material (with color-coded density) pollutes the surrounding environment and forms a thick accretion disk around the remnant object. The whole sequence covers about 0.03 s of evolution. In most cases, the heavy neutron star cannot survive its own gravity for much longer, eventually collapsing into a black hole.

Simulation & visualisation credits: Ciolfi, Giacomazzo (Virgo Collaboration), Kastaun (LIGO Scientific Collaboration).

Posted: 02/05/2019
O3 start

Virgo and LIGO join forces for a new year-long signal hunt

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O3 start O3 start

The Virgo and LIGO detectors are ready to start the new Observing run called O3, lasting a whole year. The hunt for gravitational waves is set to start on April 1st when the European Virgo detector, based in Italy at the European Gravitational Observatory (EGO), and the LIGO twin detectors, located in the state of Washington and Louisiana (USA), will start to take data becoming together the most sensitive gravitational wave observatory to date. During a one-year period the LIGO and Virgo Collaborations will register science data continuously, and the three detectors will operate as a global observatory.

"With respect to the second observation period O2, the Virgo sensitivity has improved by about a factor of 2, which means that the volume of the observable Universe has increased by a factor of 8", says Alessio Rocchi, researcher at INFN and Virgo’s commissioning coordinator.

"The quality of the data collected by the instruments is a determining factor to detect gravitational-wave signals buried into noise and to measure their properties", said Nicolas Arnaud, CNRS researcher currently seconded to EGO and Virgo detector characterization coordinator. "A lot of progress has been made in that direction since O2, thanks to the combined effort of the collaboration as a whole, from the instrumentalists to the data analysts".

The scientific output of O3 is expected to be tremendous and it will potentially reveal new exciting signals coming form new sources such as the merger of mixed binaries made by a black hole and a neutron star. The O3 run will also target long lasting gravitational waves produced for instance by spinning neutron stars which are not symmetric with respect to their axis; however, the detection of such signals is still an enormous challenge and the LIGO and Virgo Collaborations are raising up to it. Furthermore, signals for the merger of binary black holes are expected to become quite common, perhaps up to one per week. Scientists also expect to observe several binary neutron star mergers.

"The new software we have built is able to send Open Public Alerts within five minutes", says Sarah Antier, postdoc at the Université Paris Diderot and responsible of the low latency program for the Virgo Collaboration. "This will allow to follow-up the gravitational wave signal with neutrino and/or electromagnetic searches, that may lead to multimessenger discoveries. Observations of many signals as we expect during O3 will give us a census of the population of stellar mass remnants and a better understanding of the violent Universe."

Since August 2017 both LIGO and Virgo have been updated and tested. In particular Virgo has fully replaced the steel wires which were used in O2 to suspend the four main mirrors of the 3 km long interferometer: the mirrors are now suspended with thin fused-silica (‘glass’) fibres, a procedure which has allowed to increase the sensitivity in the low-medium frequency region, and has a dramatic impact in the capabilities to detect mergers of compact binary systems. A second major upgrade was the installation of a more powerful laser source, which improves the sensitivity at high frequencies. Last but not least squeezed vacuum states are now injected into Advanced Virgo, thanks to a collaboration with the Albert Einstein Institute in Hannover, Germany. This technique takes advantage of the quantum nature of light and improves the sensitivity at high frequencies.

The image shows the rear-side view of a suspended mirror. The coating reflects the Virgo near-infrared laser beam, but is transparent in the visible range. A scientist is finally releasing the safety stops used during installation. The 42kg-mass mirror is suspended from four thin fused-silica fibres, which are bonded to the sides of the mirror.

Image credit: EGO/Virgo Collaboration/Perciballi

Posted: 26/03/2019
ER14

Final testing before the 3rd Observation Run

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ER14 ER14

Today March 4th, 2019 the Advanced LIGO and Advanced Virgo detectors are starting their 14th Engineering Run. ER14 will last at least four weeks: it will be the final test before the start of the 3rd LIGO-Virgo Observation Run (O3). During the first half of the run activities will be scheduled that might still improve the three interferometres in the network. ER14 will allow scientists to perform long-term tests of the detector stability, as well as to check the readiness of the software that analyses data in real time. No automatic open public alerts will be issued during this period: any significant candidate trigger identified in the data would have to pass human vetting first.

The successful completion of ER14 will lead the path to the one year-long O3 science run: O3 will be the longest period during which the global network of advanced gravitational-wave detectors will be observing the Universe with unsurpassed sensitivity. Since the end of the O2 science run in August 2017, the LIGO and Virgo Collaborations have continued working on their instruments to improve their performance. The figure on the left shows how the sensitivity of Advanced Virgo has progressed steadily over the past months.

Posted: 04/03/2019
O2 dataset

O2 data set now available

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O2 dataset O2 dataset

LIGO and Virgo have made publicly available the strain data from the O2 observing run. These data are now available through the Gravitational Wave Open Science Center.

The O2 observing run began on the 30th of November, 2016 and ended on the 25th of August, 2017. This was the second observing run of Advanced LIGO, and the first observing run of Advanced Virgo, which joined O2 on the 1st of August, 2017.

The release includes over 150 days of recorded data from each of the two LIGO observatories, as well as 20 days of recorded data from Virgo, making this the largest data set of 'advanced' gravitational-wave detectors to date. Observations in O2 include seven binary black hole mergers, as well as the first binary neutron star merger observed in gravitational waves, all recently published in the GWTC-1 catalogue. Along with the strain data, the release contains detailed documentation and links to open-source software tools. As with previous data releases, the O2 data set should be useful for both scientific investigations and educational activities.

The figure on the left shows the sensitivity achieved during O2 of the three detectors in the network.

Posted: 28/02/2019
O3 preparation news

Advanced Virgo is progressing steadily towards the 3rd LIGO-Virgo Observation Run

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O3 preparation news O3 preparation news

Advanced Virgo scientists are preparing for the upcoming third LIGO-Virgo scientific Observation Run (O3).

Advanced Virgo and Advanced LIGO have scheduled engineering runs to prepare for O3. The four-day engineering run, ER13, was completed on the 18th of December, 2018; more details are available here.

In particular, ER13 allowed for an end-to-end test of the procedure for releasing Open Public Alerts. These alerts will notify the physics and astronomy community whenever a potential gravitational-wave transient event is observed. As these alerts need to be circulated within a short time frame, a rapid response team is charged with guaranteeing their quality.

A second engineering run, ER14, is scheduled for March 2019. ER14 will last approximately four weeks and will be followed by the third LIGO-Virgo scientific Observation Run (O3). An updated timeline can be found here.

Advanced Virgo has to improve further in terms of sensitivity and stability of operation in order to meet O3 requirements. One of the ER14 milestones will be the enhancement of Advanced Virgo sensitivity through the use of squeezed-light. More details about Advanced Virgo upgrades are listed here.

The picture on the left shows a detail of the optics used to inject the squeezed-light into Advanced Virgo.

Posted: 22/01/2019
ER13

LIGO and Virgo make another joint step towards the start of the next Observation Run

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ER13 ER13

Today, Friday December 14th 2018, the 13th Engineering Run (named 'ER13') has started. It will last four days until next Tuesday, the 18th of December.

During ER13, the Advanced Virgo and Advanced LIGO detectors will operate together, forming a world-wide network. The purpose of this run is to check the progress achieved so far and to collect indications on how to further tune the detectors, the online data analysis pipelines, and the procedure for releasing Open Public Alerts, which will notify the physics and astronomy community when a potential gravitational-wave transient event has been observed.

For more information, please click here.

The third LIGO-Virgo scientific Observation Run (O3), the goal of which will be to make astrophysical observations, will follow one more Engineering Run - ER14 - which is scheduled to take place a few months from now. An updated timeline towards O3 can be found here.

Since the end of August 2017, when the successful second Observation Run (O2) concluded, Virgo and LIGO scientists have been working intensively on the interferometric detectors and associated algorithms with the aim of improving observation capabilities. More details about Advanced Virgo upgrades are listed here.

O2 was a great success, bringing with it the first ever events measured by the global 3-detector network - such as GW170814, GW170817 (the first detection of gravitational waves produced by colliding neutron stars) and GW170818 (another triple detection of a binary black hole merger recently made public). It was also the birth of multi-messenger astronomy with gravitational waves. Overall, the LIGO and Virgo collaborations have now confidently detected gravitational waves from a total of 10 stellar-mass binary black hole mergers and one merger of neutron stars: the collaborations have just released their first catalog of gravitational-wave events GWTC-1 (more information is available here).

"ER13 is the first common Virgo-LIGO milestone towards O3", says Alessio Rocchi of the Italian National Institute for Nuclear Physics (INFN) who is coordinating the commissioning efforts of the Virgo Collaboration. "It represents an essential step towards the Open Public Alert era and is the first occasion on which all of the infrastructure of the EGO observatory will be thoroughly tested. Thanks to the hardware upgrades installed over the last year and the commissioning activities, the Virgo sensitivity has increased by about 60% with respect to O2. Thus, we might even expect some surprises."

The composite image on the left shows the sun setting over Virgo at the European Gravitational Observatory (EGO) near Pisa, Italy, and a typical scene in the Virgo Control Room; the place in which many of the scientists engaged in the commissioning of the detector carry out their work. It is also where they all meet on a daily basis to discuss issues, activities and the latest news related to the detector.

Posted: 14/12/2018
O2 catalog paper news

LIGO and Virgo Announce Four New Gravitational-Wave Detections

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O2 catalog paper news O2 catalog paper news

On Saturday 1st December 2018, scientists attending the Gravitational Wave Physics and Astronomy Workshop in College Park, Maryland, presented new results from searches for coalescing cosmic objects, such as pairs of black holes and pairs of neutron stars, by the LIGO and Virgo detectors. The LIGO and Virgo interferometers have now confidently detected gravitational waves from a total of 10 stellar-mass binary black hole mergers and one merger of neutron stars, which are the dense, spherical remains of stellar explosions. Seven of these events had been reported before, while four of the black hole detections are newly announced.

From September 12, 2015, to January 19, 2016, during the first LIGO observing run since undergoing upgrades in a program called Advanced LIGO, gravitational waves from three binary black hole mergers were detected. The second observing run, which lasted from November 30, 2016, to August 25, 2017, yielded a binary neutron star merger and seven additional binary black hole mergers, including the four new gravitational wave events being reported now. The new events are known as GW170729, GW170809, GW170818 and GW170823 based on the dates on which they were detected.

The Virgo interferometer joined the two LIGO detectors on August 1, 2017, while LIGO was in its second observing run. Although the LIGO-Virgo three-detector network was operational for only three-and-a-half weeks, five events were observed in this period. Two events detected jointly by LIGO and Virgo, GW170814 and GW170817, have already been reported.

One of the new events, GW170818, detected by the global network formed by the LIGO and Virgo observatories, was precisely pinpointed in the sky. The sky position of the binary black holes, located about 2.5 billion light-years from Earth, was identified with a precision of 39 square degrees. That makes it the next best localized gravitational-wave source after the GW170817 neutron star merger.

The figure on the left shows the localizations of the various gravitational-wave detections in the sky. The triple detections are labelled as HLV, from the initials of the three interferometers (LIGO-Hanford, LIGO-Livingston and Virgo) that observed the signals. The reduced areas of the triple events demonstrate the capabilities of the global gravitational-wave network.

Science Papers and supplementary materials

Posted: 03/12/2018
May 2018 News

Upgrading and commissioning the Virgo detector

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May 2018 news May 2018 news

As planned, the Virgo and LIGO detectors stopped taking data for the ‘Observation Run 2’ - O2 - on the 25th of August, 2017. For both collaborations, this marked the beginning of a new and busy period, which is scheduled to last at least one year (see timelines on the left). During this time, the sensitivity of all three instruments (that is, their ability to detect signals even fainter than those observed in 2015 and 2017 or coming from similar sources, but located further away in the universe) should be improved significantly. Then, in early 2019, the data-taking period – O3 – will start and last for about one calendar year.

For more information, please click here.

On the Virgo side, three phases were foreseen.

First, commissioning activities were undertaken until mid-autumn, in order to improve our knowledge of the detector configuration that was used to take data, and to fix issues identified during the August 2017 run. Indeed, for all large facilities such as Virgo, the golden rule is to disturb the instrument as little as possible while it is running. Only issues preventing the taking of data are promptly fixed and only straightforward improvements are allowed. Therefore, it was only after the end of the O2 run that people working in the Virgo control room were able to carry out many different tests and modify the hardware and software configurations of the detector.

Instrument upgrades were implemented from the end of November 2017 until the middle of March 2018. Several pieces of hardware were replaced or modified. Notable upgrades included:

  • The installation of a more powerful, ultra-stable input laser: the larger the power circulating in the detector, the more sensitive it is, in particular in the high-frequency range: above a few hundred hertz. With the new laser, the O3 input power is expected to increase by up to a factor of three in comparison with the O2 data-taking period.
  • The replacement of the steel wires suspending the mirrors forming the 3-km long Fabry-Perot cavities - four mirrors in total - with fused silica - ‘glass’ - wires. This lower-dissipation material helps in reducing friction at the anchor levels, hence the suspension thermal noise, which represents the dominant fundamental noise impacting upon the Virgo sensitivity in the medium-frequency region, where it is at its best. These fibers have high breaking strengths, but they are fragile, which makes the whole process - from the production of the fibers in a dedicated lab at EGO, to the suspension of the mirror from its superattenuator structure - challenging. In parallel, the vacuum quality has been improved. About a year and half ago, particle contamination of the vacuum caused some fused-silica fibers to break inside the detector. At that time, the mirrors were again suspended from steel wires and the upgrade to fused-silica fibers was postponed to the O2-O3 long shutdown.
  • The addition of a squeezed vacuum source - a ’squeezer’ - provided by the Albert Einstein Institute in Hannover, Germany. This instrument, installed at the output port of the interferometer - where the power exists that results from the interference between the laser beams circulating in the 3-km long arms - helps to ’beat’ the quantum noise limit, i.e. to reduce the laser shot-noise, which is dominant at high frequency, below its normal level. This counter-intuitive effect is due to the quantum nature of light: any electromagnetic wave, such as the Virgo laser beam, is defined by two quantities, an amplitude and a phase, both of which are fluctuating. The fluctuations of the phase – also known as ’phase noise’ – matter more than the amplitude fluctuations for Virgo. With a squeezer, one can move part of the phase noise to the amplitude noise – the Heisenberg principle states that one cannot decrease both fluctuations: if one goes down, the other should increase – and hence improve the instrument sensitivity. This technique has been successfully implemented in GEO 600 and LIGO: this is the first time it will be tried in Virgo.

Following the completion of all of these upgrades, Virgo is now back in commissioning mode. The first aim is to learn how to control the detector, which has been significantly modified, and then to improve the sensitivity – by at least a factor of two by the end of the year. This will be challenging but the first results are promising: the best O2 sensitivity – the all-time record sensitivity for Virgo – was surpassed in early June.

Posted: 17/07/2018
GW170817

LIGO and Virgo make first detection of gravitational waves produced by colliding neutron stars

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GW170817 GW170817

Discovery marks first cosmic event observed in both gravitational waves and light.

For the first time, scientists have directly detected gravitational waves — ripples in space and time — in addition to light from the spectacular collision of two neutron stars. This marks the first time that a cosmic event has been viewed in both gravitational waves and light.

The discovery was made using the U.S.-based Laser Interferometer Gravitational-Wave Observatory (LIGO); the Europe-based Virgo detector; and some 70 ground- and space-based observatories.

The image shows the localization of the gravitational-wave (from the LIGO-Virgo 3-detector global network), gamma-ray (by the Fermi and INTEGRAL satellites) and optical (the Swope discovery image) signals from the transient event detected on the 17th of August, 2017. The colored areas show the sky localization regions estimated by the gamma-ray observatories (in blue) and by the gravitational-wave detectors (in green). The insert shows the location of the apparent known galaxy NGC4993: on the top image, recorded almost 11 hours after the gravitational-wave and gamma-ray signals had been detected, a new source (marked by a reticle) is visible: it was not there on the bottom picture, taken about three weeks before the event.

Science Papers and supplementary materials

GW170814

Straight to the source: the LIGO-Virgo global network of interferometers opens a new era for gravitational wave science

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GW170814 GW170814

A fourth gravitational-wave signal coming from the merger of two stellar mass black holes located about 1.8 billion light-years away was detected on the 14th of August 2017, at 10:30:43 UTC. GW170814 is the first event observed by the global 3-detector network, including not only the two twin Advanced LIGO detectors but the Advanced Virgo detector as well.

Following a multi-year upgrade programme and several months of commissioning, the Advanced Virgo detector joined the LIGO "Observation Run 2" data-taking period on the 1st of August. The three instruments worked together until the 25th of August.

GW170814 demonstrates the potential of a 3-detector network, both in terms of localization of a source in the sky and in terms of the testing of Einstein's theory of general relativity. The best GW170814 skymaps, computed by an analysis that uses all of the available information from the three instruments, cover just 60 square degrees (to be compared with several hundreds of square degrees for the LIGO-only network) and GW170814 data have allowed the LIGO-Virgo collaboration to probe, for the first time, the polarization of gravitational waves.

Therefore, GW170814 holds great promise for the future of multimessenger astronomy. Additional results, based on data from the three-detector network, will be announced in the near future by the LIGO-Virgo Collaboration; the analysis of the data is currently being finalized.

Posted: 27/09/2017
DQ_META_ITF_Mode O2 stripchart

A very exciting LIGO-Virgo Observing run draws to a close on the 25th of August

DQ_META_ITF_Mode O2 stripchart DQ_META_ITF_Mode O2 stripchart

The Virgo and LIGO Scientific Collaborations have been observing since November 30, 2016 in the second Advanced Detector Observing Run ‘O2’, searching for gravitational-wave signals, first with the two LIGO detectors, then with both LIGO and Virgo instruments operating together since August 1, 2017. Some promising gravitational-wave candidates have been identified in data from both LIGO and Virgo during our preliminary analysis, and we have shared what we currently know with astronomical observing partners. We are working hard to assure that the candidates are valid gravitational-wave events, and it will require time to establish the level of confidence needed to bring any results to the scientific community and the greater public. We will let you know as soon we have information ready to share.

The picture shows the Virgo duty cycle during the whole data taking period: we have been taking science data more than 80% of the time over four weeks!

Posted: 25/08/2017
First detection

First detection of gravitational waves

First detection First detection

On the 14th of September 2015, a gravitational wave was detected for the first ever time. This first detection was announced to the world on the 11th of February 2016:

Posted: 11/02/2016

About

Working in the tower

What is Virgo?

Virgo is an interferometric gravitational-wave antenna. It consists of two 3-kilometre-long arms, which house the various machinery required to form a laser interferometer.

A beam-splitter divides a laser beam into two equal components, which are subsequently sent into the two interferometer arms. In each arm, a two-mirror Fabry-Perot resonant cavity extends the optical length from 3 kilometres to approximately 100. This is because of multiple reflections that occur within each cavity and which consequently amplify the tiny distance variation caused by a gravitational wave.

The two beams of laser light that return from the two arms are recombined out of phase so that, in principle, no light reaches the so-called 'dark fringe' of the detector. Any variation caused by an alteration in the distance between the mirrors, produces a very small shift in phase between the beams and, thus, a variation of the intensity of the light, which is proportional to the wave's amplitude.

Click here for more information on the Virgo experiment and its science.

The Virgo Collaboration

Virgo is a gravitational-wave interformeter designed, built and operated by a collaboration made up of 20 laboratories in 6 countries and involves the following institutions:

CNRS INFN NIKHEF EGO WIGNER IMPAS VALENCIA

Virgo Outreach

Interesting events are always being prepared at EGO-Virgo. Please view our Outreach website for details on up and coming, as well as recent, events.

Virgo and LIGO

Virgo and the LIGO Scientific Community work together in many areas and have a specific agreement on the exchange of data. More information on the work of our LIGO colleagues is available here.

More information on the identification and follow up of electromagnetic counterparts of gravitational wave candidate events is available here.

The Virgo-EGO Scientific Forum

Virgo and EGO have also established a scientific forum - the VESF - for astrophysicists and theorists, dedicated specifically to the furthering of scientific knowledge related to Virgo. More information is available here.

A payload

ET - Einstein Telescope

The Einstein Telescope (ET) project is dedicated to the development of a critical research infrastructure for a third-generation gravitational-wave interferometer. More information about the project, which is supported by the European Commission as part of the Framework Programme 7, is available here.

Other gravitational-wave experiments

Have a look at some of the other gravitational wave experiments:

Interferometric experiments

Pulsar-timing-array experiments

Other gravitational-wave-related websites

Jobs & Fellowships

The following roles are currently being advertised within the Virgo Collaboration:

Roles at EGO are advertised on the EGO website.

Visits

Virgo viewed from the south

Events

If you are looking for information on an up-coming or recent event, please visit our Outreach website.

Opening hours

The Reception at the EGO site is open at the following times:

  • Monday to Friday, from 08:30 to 13:00 and 14:00 to 17:30
  • Closed on Saturdays and Sundays (except when site visits are scheduled)

How to get to Virgo

Virgo is at the site of the European Gravitational Observatory (EGO), the organisation responsible for the site, and is located in:

Via Amaldi
56021 Santo Stefano a Macerata – Cascina (Pisa), Italy.

As Virgo is located in the countryside, it is not particularly easy to access without a car, as there are no public transport links directly to it.

Arriving by car

The EGO-Virgo site GPS coordinates (in DD) are:

  • Latitude: 43.6305 N
  • Longitude: 10.5021

Arriving by plane/train and taxi

The nearest airport to Virgo is Pisa Galileo Galilei International Airport.

If you are travelling by aeroplane and arrive at the Pisa Galileo Galilei International Airport, or by train and arrive at Pisa Central train station, we recommend that you call a taxi (Co.Ta.Pi Radiotaxi Pisa, +39 050 54 16 00) complete your journey to EGO-Virgo.

It takes about 20-30 minutes to reach the site coming from Pisa when coming by car. The taxi fare from Pisa to the EGO-Virgo site costs about €35-40.

What do on arrival at the EGO-Virgo site

All visitors must present themselves at the site-entrance gate, where they will be met by their EGO contact person.

Visitors' vehicles may be parked at the site, in the appropriate parking areas.

New Virgo collaborators

New Virgo collaborators must complete the association and safety procedures before starting any activity on site. To this end, they should contact the EGO Administration (Building 4, first floor, +39 050 752 522/325) and the Safety and Security Office (Building 1, +39 050 752 416/544).

Badges to access the site and an account to access the Virgo documentation will only be granted by the IT department on completion of this process.

Contact

The Virgo experiment at the European Gravitational Observatory

Address: Via Amaldi, 56021 Santo Stefano a Macerata, Cascina (Pisa), Italy.

Phone: +39 050 752 511

Fax: +39 050 752 550

Email: info@ego-gw.it

Web: http://www.virgo-gw.eu

Twitter: https://twitter.com/ego_virgo

Facebook: https://it-it.facebook.com/EGOVirgoCollaboration/

Youtube: EGO & the Virgo Collaboration - LIGO-Virgo

Instagram: LIGO-Virgo

Jo van den Brand, Spokesman of Virgo

Phone: +31 620 539 484

Email: jo@nikhef.nl

Web: https://www.nikhef.nl/~jo

Addresses: Nikhef, National Institute for Subatomic Physics, Amsterdam, The Netherlands.
VU University Amsterdam, Faculty of Sciences, Department of Physics and Astronomy.
European Gravitational Observatory - EGO, Cascina (PI), Italy.

The Virgo Collaboration

A full list of members of the Virgo Collaboration and their contact details is available here.

Please get in contact if you would like more information.