Aerial view of the EGO site, location of the Virgo interferometer
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LIGO-Virgo observation period suspended because of COVID-19

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The LIGO Scientific Collaboration and the Virgo Collaboration (the LVC) have agreed to suspend their third observation period, named O3, which has been running since the 1st of April, 2019. The suspension, which will be effective within one week, is motivated by the worldwide COVID-19 pandemic. Public health and worker safety are always the top priority for the LVC.

"It is certainly difficult to be obliged to suspend the run at the moment that Virgo had reached maximum sensitivity and a quasi-faultless operation", says Stavros Katsanevas, director of the European Gravitational Observatory (EGO) that hosts Virgo, "but the first priority of the worldwide collaboration and the EGO-Virgo managements in particular, is to preserve the health of the people; both those working at the site and the public at large. Here I cannot but praise the composure, the calmness and the dedication to the task, of the people on site, with the EGO operators first at the line-front, who have operated the detector these last few weeks, in the difficult conditions we all know. This is certainly a good augur for the restart of the operations, when the conditions permit it."

"Even though we had suspend the run early, O3 has been tremendously successful, thanks to the collective efforts of the LVC", says Jo van den Brand, spokesperson of the Virgo Collaboration, from Nikhef, Amsterdam and professor at Maastricht University in The Netherlands. "The discovery of GW190425, the second observation of a gravitational-wave signal consistent with the merger of a binary-neutron-star system after GW170817, has already been reported."

Much more is expected to be discovered as scientists work on the analysis of the data collected during the run: 56 detection candidates have already been announced as public alerts, as reported in the freely accessible 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 astronomy, pioneered with the GW170817 event.

O3 had been planned to last for one full year and, taking into account a one-month break, in October 2019, which was dedicated to commissioning activities, had been due to end on the 30th of April, 2020.

Image: The control room of Advanced Virgo at the European Gravitational Observatory, near Pisa (Italy). Shown in the foreground is an EGO operator working on shift to keep the detector running. Usually a lively environment, the control room is now minimally populated because of the COVID-19 pandemic. The image shows only one Virgo scientist working, Julia Casanueva, in the control room along with the EGO operator, Fabio Gherardini.

Image credit: EGO/Virgo Collaboration

Posted: 25/03/2020
A binary neutron star system just before merger: the two stars are deformed by tidal forces and are about to fuse together. The image is produced by a numerical simulation in General Relativity and shows the mass density volume rendering at nuclear densities in blue and lower density material in red. The snapshot refers to the central volume of approximately 45^3 km.

GW190425: the merger of a compact binary with total mass of about 3.4 Msun

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A binary neutron star system just before merger: the two stars are deformed by tidal forces and are about to fuse together. The image is produced by a numerical simulation in General Relativity and shows the mass density volume rendering at nuclear densities in blue and lower density material in red. The snapshot refers to the central volume of approximately 45^3 km. A binary neutron star system just before merger: the two stars are deformed by tidal forces and are about to fuse together. The image is produced by a numerical simulation in General Relativity and shows the mass density volume rendering at nuclear densities in blue and lower density material in red. The snapshot refers to the central volume of approximately 45^3 km.

On April the 25th, 2019, the network of gravitational-wave (GW) detectors formed by the European Advanced Virgo, in Italy, and the two Advanced LIGO, in the US, detected a signal, named GW190425. This is the second observation of a gravitational-wave signal consistent with the merger of a binary-neutron-star system after GW170817. GW190425 was detected at 08:18:05 UTC; about 40 minutes later the LIGO Scientific Collaboration and the Virgo Collaboration sent an alert to trigger follow-up telescope observations.

The source of GW190425 is estimated to be at a distance of 500 million light years from the Earth. It is localized in the sky within an area about 300 times broader than was the case for the BNS observed by LIGO and Virgo in 2017, the famous GW170817, which gave birth to multi-messenger astrophysics. However, unlike GW170817, no counterpart (electromagnetic signals, neutrinos or charged particles) has been found to date.

There are a few explanations for the origin of GW190425. The most likely is the merger of a BNS system. Alternatively, it might have been produced by the merger of a system with a black hole (BH) as one or both components, even if light BHs in the mass-range consistent with GW190425 have not been observed. Yet, on the basis solely of GW data, these exotic scenarios cannot be ruled out. The estimated total mass of the compact binary is 3.4 times the mass of the Sun. Under the hypothesis that GW190425 originated from the merger of a BNS system, the latter would have been considerably different to all known BNS in our galaxy, the total mass range of which is between 2.5 and 2.9 times the mass of the Sun. This indicates that the NS system that originated GW190425 may have formed differently than known galactic BNSs.

"After the surprise of the initial results", says Alessandro Nagar of the Istituto Nazionale di Fisica Nucleare (INFN) of Turin, Italy, "we have finally reached a reliable understanding of this event. Although predicted theoretically, heavy binary systems like those that might have originated GW190425 may be invisible through electromagnetic observations."

"While we did not observe the object formed by the coalescence, our computer simulations based on general relativity predict that the probability that a BH is formed promptly after the merger is high, about 96%", says Sebastiano Bernuzzi of the University of Jena, Germany.

Image: A binary neutron star system just before merger: the two stars are deformed by tidal forces and are about to fuse together. The image is produced by a numerical simulation in General Relativity (animation) and shows the mass density volume rendering at nuclear densities in blue and lower density material in red. The snapshot refers to the central volume of approximately 45 km in diameter.

Image credit: CoRe / Jena FSU

Press release - Communiqué de presse - Notas de prensa - Materiały dla prasy

Posted: 06/01/2020

O3 restarts

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Advanced Virgo and the two Advanced LIGO detectors resume the taking of science data on the 1st of November, 2019, following a one-month-long stop. This event marks the restart of the third observation period, named O3, which started on the 1st of April, 2019. All three of the interferometers in the global gravitational-wave observatory paused O3 on the 1st October, 2019, in order to work on improvements to enhance the performance of the detectors.

On the Virgo side, the focus was on increasing the laser power injected into the interferometer, from 19 W to 26 W. This increase has been effective in improving the detector sensitivity at high frequencies, but has required a complete re-tuning of the interferometer.

Effort was also devoted to the study of selected noise sources. The lessons learned will be useful for the future operation of the instrument.

"The month of commissioning has been quite intense. We performed many activities, both to better understand the noise that limits the sensitivity and to handle a 30% increase in the laser input power", says Matteo Tacca, researcher at Nikhef in The Netherlands, and the Virgo Commissioning Coordinator.

"We were able to find the sources of some of the noise limiting Virgo’s sensitivity. A few of them have been removed, while others require further measurements. Also mitigation strategies are under investigation. After a lot of work fine-tuning the interferometer, we were able to recover stable operation with higher input power".

Many activities were also performed at the two LIGO detectors in the US, such as the installation of special fences at the Hanford site in order to reduce wind noise. For more information see ligo.org.

O3 will now run with no further interruptions until the 30th of April, 2020.

Image: Scientist at work in the Advanced Virgo detection area, investigating noise caused by scattered light. The pipes in the picture have been temporarily equipped with monitoring accelerometers and actuators in order to perform diagnostic measurements Virgo laser source.

Image credit: EGO/Virgo Collaboration/Francescon

Posted: 04/11/2019
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".

For more information, please click here.

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.

Image: 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
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

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:

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.