Gravitational wave mission LISA selected by ESA Science Program Committee

ESA (the European Space Agency) has chosen the Laser Interferometer Space Antenna (LISA) for its third large-class mission (L3) in the agency’s Cosmic Vision science program. The LISA trio of satellites is meant to study gravitational waves in space.

This is a major milestone in the development of LISA. The next big step will be the adoption, expected around 2021/2022.

In France, the APC Laboratory has a central role in LISA, since today the laboratory is coordinating, with the support of CNES and other partner laboratories, the two main French contributions considered for LISA: setting up of the Scientific Data Treatment Centre, and the Performance Management, Integration & Payload Tests.

For more information:

ESA web

NASA web

Photo Lisa concept
AEI/Milde Marketing/Exozet

Grant Pierre Binétruy

As many of you have expressed the wish to contribute somehow to the continuation of Pierre Binétruy’s work, we have conceived the project to create a research grant bearing his name.

If thus you wish to make a gift on behalf of Pierre, we suggest you participate in the creation of this research grant bearing his name. All donations received since April 1st 2017 will fund this grant.

Donations to the Grant Pierre Binétruy can be made to the Endowment Fund Physique de l’Univers which he directed: Your donations to the grant Pierre Binétruy

Pierre Binétruy passed away

It is with great sadness that we must announce the death of our friend and colleague Pierre Binétruy on the first day of April.

French, European and world science has lost one of its most exemplary practitioners but also an exceptional human being.


Pierre Binétruy, born in 1955, received his doctorate in 1980 under the direction of Mary K Gaillard, entitled “Theoretical and Phenomenological Aspects of Gauge Theories”. From 1979 to 1986 he held several positions at CERN (fellow) and in the United States (University of California at Berkeley, University of Florida, University of Chicago). In 1986, he was recruited as a researcher at the LAPP, Annecy-le-Vieux and 4 years later as a professor at the University of Paris XI in the Laboratory of Theoretical Physics, where he became a professor of exceptional class in 1999. Since 2003 he was a professor at the  University Paris Diderot.

His main interests have evolved from high energy physics (notably supersymmetry) to cosmology and gravitation, and in particular the interface between the study of the primordial Universe and the theories of fundamental interactions. His recent interests included inflation models, dark energy, and gravitational wave cosmological backgrounds. During his prolific career, he published seminal papers that approached the 1000 citations each. For his research he has received several awards (Thibaud Prize, Paul Langevin Award from French Physical Socienty, Miller Professor 1996 in Berkeley). He was one of the most brilliant theorists of his time.

But his memory will also remain because, to paraphrase Andre Malraux, he combined “spirit and courage”, since he knew that it was necessary not only to seek scientific truth but also to have the courage to organize the community for the scientific goals that this truth imposes and also fight within the institutions to defend them.

The oldest members remember the extraordinary intellectual atmosphere that animated the Supersymmetry Research Group (GDR), which he proposed and directed from 1997 to 2004, transforming it into an unprecedented crossroad for experimenters and theorists, a melting pot of new ideas of both theory and of experimental analysis at the turn of the century.

He also had the central intuition,  towards mid-2015,  a time when the detection of gravitational waves was for many a distant dream to involve France through CNES in the space program of detection of gravitational waves: LisaPathfinder and Lisa. A scientific choice to which he devoted a great part of his dynamism and this until and during the days of his hospitalization.

APC researchers and engineers also remember the energy and dynamism that he put into the foundation of the Astroparticle and Cosmology Laboratory (APC) since 1999, following an incentive from Luc Valentin. He was the director of the APC until 2013. He accompanied this original endeavor of the Paris Diderot University and the IN2P3 / CNRS, the CEA and the Observatoire de Paris, with an inexhaustible inventiveness. We owe to him the firm involvement of the laboratory to Space Sciences, the interdisciplinary opening to the Earth Sciences, the realization of the importance of Data Sciences with the François Arago Center, the foundation with George Smoot, Nobel Prize in Cosmology,  of the Paris Center for Cosmological Physics (PCCP) and the immersion of the APC in a global network of equivalent centers  of excellence (for example, the Associated International Laboratory with KIPAC at SLAC, relations with the University of Chicago or KIT/Helmholtz at Karlsruhe).

He was also a professor, who inspired hundreds of students, and through the MOOC Gravity, in collaboration with G. Smoot, his courses reached thousands (96,000 enrolled). The expression of gratitude of the students but also of all those who followed him warmed the heart of Pierre but also of us, his colleagues. This MOOC was considered by Pierre  an avenue for the future; not a simple way to improve the visibility of the University, but a revolution in the way knowledge is diffused, similar to this of typography, and this revolution meant perhaps a new type of universities, and through them of society and humanity.

In parallel to these activities  (only four examples were chosen from among a multitude) Pierre found time to be president of the Fundamental Physics Advisory Group (2008-2010) and the Fundamental Physics Roadmap Committee (2009-2010) of ESA; the French consortium of the LISA space mission;  the Theory Division of the French Physical Society (1995-2003); the interdisciplinary section of the Astroparticle (2003-2004) and the Theory sections (2005-2008) of the CNRS. He was  finally the Director of the Endowment Fund “For Research and Training in the Physics of the Universe”.

He was also a member of the IN2P3 Scientific Committee (1996-2000), the APPEC Scientific Advisory Committee, the ApPIC working group of IUPAP, which he helped to create in 2013 and of which he was a key member until today, of the European Space Science Committee, the Scientific Program Committee (SPC) of the SLAC National Laboratory, the Evaluation Committee of the DOE Roadmap and the International Evaluation Committee of INFN (Italy) and NSERC (Canada). Finally, in recent years, he was a member of the CNRS Scientific Council.

This activity, pursued with enthusiasm and unfailing rigor, was accompanied by a great culture and sophistication, a profound knowledge of the arts, where he propelled several actions between art and science, and especially a great human quality. This quality has made that the news of his disappearance has been lived with great sadness throughout the world. As one of his eminent colleagues said of him: “Peter was one of those very exceptional people who was at the top of the game and, at the same time, a remarkably pleasant colleague. “

French science but also Europe and  the world has lost one of its exemplary practitioners.

Stavros Katsanevas APC Laboratory Director

A new session of Gravity! starts on Monday 30th January

Classes for the third session of the on-line course Gravity! start on Monday 30th January, for six weeks. You may register here on the FutureLearn platform. The course is free and registration is open to everyone.

Since its first run, this course has attracted close to 90 000 learners, including both French and English versions. This new session follows the same programme. It revisits the emergence of the main concepts from Galileo to Newton and Einstein before discussing some of the main aspects of gravity in the Universe – Big Bang, expansion and cosmic inflation, cosmic microwave background, dark matter, dark energy, black holes, ending with gravitational waves, whose detection was announced in February 2016. This will certainly be the climax of this course!

Gravity! is for all those of you curious about the mysteries of the Universe and invites you to understand, without any prerequisite in physics, the foundations of Einstein’s theory that makes gravity “the engine of the Universe”.

The Gravity! course is produced by the Paris Centre for Cosmological Physics and the Endowment Fund Physics of the Universe from Paris Diderot University.

Two members of the Gravity! team are awarded a L’Oréal-UNESCO fellowship for Women in Science

On October 12 were announced in Paris the L’Oréal-UNESCO Fellowships for Women in Science. Each year, these awards allow talented young woman scientists to pursue promising research projects. Two members of the Gravity! team were honored at this occasion.


Valerie Domcke is a PCCP fellow at Université Paris Diderot. She received her Ph.D. in theoretical physics from the University of Hamburg, then went to Trieste for a postdoctoral position before joining the Paris Centre for Cosmological Physics (PCCP) in October 2015. She is presently working on the physics of the early Universe and on gravitational waves. She is particularly interested in the connection between particle physics and the physics of the Universe

Eleonora Capocasa is presently doing her Ph.D. at APC laboratory in the Virgo team (as a member of the LIGO-Virgo collaboration, she signed the gravitational wave discovery paper last February). She is working on ways to increase the sensitivity of gravitational wave detectors.

Congratulations to both of them! And let us make the wish that their example will attract many more young women scientists to the field of gravitational wave astrophysics.

A proton’s life



One of our pleasures is to discover some real gems among the posts  of the Gravity! course. We already have a great collection. As a tribute to all of you who made brilliant contributions, we decided to highlight the beautiful story that Damien Pigret, a talented participant to the second session of Gravité!, proposed on the course forum. Because this is still summer,  we propose this delightful story as a series, A proton’s life, published in 4 installments every Monday. Enjoy!

Pierre Binétruy

Gravitational waves strike the Earth again: GW151226

The LIGO and Virgo collaborations announced today, June 15, at the 228th meeting of the American Astronomical Society in San Diego, a new gravitational wave event. Simultaneously, an article is published in Physical Review Letters.

The event was observed on December 26, 2015 at 3.38.53 UTC in the two LIGO detectors of Livingstone and Hanford (1.1 millisecond later). The event, interpreted as the merger of two black holes, is not as bright as the one announced last February, and thus the signal is not as spectacular:


One of the reasons is that the black holes are not as massive as in the “discovery” event GW150914: the two masses are 14 and 8 solar masses, and the final black hole mass is 21 solar masses. The analysis is using templates of mergers predicted by theory, and comparing the signal with them. The signal to noise ratio (the quantitative way physicists express the fact that the signal stands out of the background “noise” in the detector) is computed to be 13, to be compared with 24 in the case of GW150914.

The distance of the event is estimated to be 1.4 billion light years.

Because the signal lasts longer in the detector than the first event observed, the LIGO-Virgo collaboration could determine that one of the initial back holes (and the final one) was spinning.

In the press conference at the AAS meeting, the collaboration reminded everyone of another event (already mentioned in the original discovery paper) which is presumably another black hole event merger. They call it LVT151012, where LVT stands for LIGO Virgo Trigger (it was observed on October 12 2015). The signal to noise ratio is 9.7 and the collaboration does not feel confident enough to call it a discovery. If it corresponded to a black hole merger, the mass of the final black hole would be 35 solar masses.

If the announcement of February 11 was closing one hundred years of quest for gravitational waves, the announcement of today clearly opens the era of gravitational waves astronomy.

We will have a great occasion to talk about this new discovery in the hangout held this Thursday 16 June, as a conclusion of the Gravity! course second session.

Thursday June 16: Gravity! hangout from Stanford on black holes and gravitational waves

Pierre Binétruy and George Smoot invite you to participate to the final hangout of the second session of the Gravity! course. This hangout will focus on black holes and gravitational waves. It will be broadcasted this Thursday June 16 at 19h00 UTC (20h00 London, 21h00 Paris, 12h00 California), live from the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) at SLAC, Stanford University.

KIPAC_logoThe Google Hangout will be streamed live on Google Hangouts and Youtube for approximately 60 minutes, where you can follow the questions and answers live. If you are not registered in this session of Gravity! you may ask your questions below or on Twitter using#FLGravity.

Two highlights for this hangout will be the recent publication of the first results by the LISAPathfinder mission, as well as the exciting new result of the LIGO-Virgo collaboration announced on June 15.

Our guests for this event will be:


Tom Abel is the director of the Kavli Institute for Particle Astrophysics and Cosmology, joint laboratory of the SLAC National Laboratory and Stanford University. His group explores the first billion years of cosmic history using ab initio supercomputer calculations. He has shown from first principles that the very first luminous objects are very massive stars and has developed novel numerical algorithms using adaptive-mesh-refinement simulations that capture over 14 orders of magnitude in length and time scales.  Most recently he is pioneering novel numerical algorithms to study collisionless fluids such as dark matter.



Roger Blandford, a native of England, held a faculty position at Caltech since 1976 when, in 2003, he moved to Stanford University to become the first Director of the Kavli Institute of Particle Astrophysics and Cosmology. He is a world-renrecognized expert in black hole astrophysics, cosmology, gravitational lensing, cosmic ray physics and compact stars.



michael_landryMichael Landry is Detection Lead Scientist with the LIGO Hanford Observatory in Washington state, and a physicist with the California Institute of Technology. Michael began work in the field of gravitational wave physics as a postdoc with Caltech in 2000, stationed at the LIGO Hanford Observatory, and has remained there as a scientist since that time. From 2010 to 2015, he led the installation of the Advanced LIGO detector at Hanford. This collaborative work, done by the LIGO Scientific and Virgo Collaborations totaling a thousand people, culminated in the first direct detection of gravitational waves from a binary black hole merger, announced Feb 11, 2016.



Stefano Vitale is the Principal Investigator (P.I.) of the LISAPathfinder mission. He is professor at the University of Trento in Italy and is a key figure of the gravitational wave community in Europe. He worked on the cryogenic acoustic detector AURIGA before joining the LISA mission where he is leading the Italian effort. He has developed in Trento a laboratory which contributed the inertial sensor onboard the LISAPathfinder mission.

LISAPathfinder exciting first results: green light for the LISA mission

The first results of the LISAPathfinder mission were presented this Tuesday June 7 in a press conference organized by ESA and published in Physical Review Letters. And they are even better than was anticipated.

This technological mission was launched on December 3 from Kourou (see the launch  and meet the technical team who participated in a Gravity! hangout  a few hours before launch).

This mission tests one key aspect of the future space gravitational wave observatory, known as LISA: it measures the variation, due to a passing gravitational wave, of distances between test masses  which are in free fall i.e. which follow purely gravitational trajectories. To protect the masses from any perturbation, there is a clever set up, known as “drag free”. It consists in using the satellite for protecting the test mass placed in its centre from any perturbation.

To understand how it works, imagine that a micrometeorite hits the satellite: the satellite moves sideways, the test mass is thus no longer in its centre, the satellite detects this anomaly through sensors, it ignites some micro thrusters to reposition itself around the test mass.

Of course, such a device is never perfect, and the test mass feels some tiny perturbations, but the goal of the LISAPathfinder is to show that the perturbations are small enough that they still allow to have confidence in the detection of gravitational waves.

Quantitatively, the goal is to minimize the stray forces acting on the test masses. But a force induces an acceleration and the goal of LISAPathfinder is to minimize the stray acceleration (one talks of an acceleration noise). The initial goal of the mission was to reach over periods of 1000 seconds a stray acceleration which is smaller than 10-13 times g, the local acceleration due to the Earth gravity.




How to realize this? In the future LISA mission, the test masses are placed at the centre of each satellite, 5 million kilometers apart  from one another. Laser beams connect the three satellites, thus forming a huge triangle. Relative variations of distance are measured by interferometry, just as for ground detectors, such as LIGO.



In LISAPathfinder, one arm of the future LISA mission is reduced to 38 cm in order to locate two test masses into a single spacecraft. The distance between these two masses is monitored by laser beams that form an interferometer very similar to the one on board LISA (apart from the distance covered by the beams).  You can find below a video provided by ESA that explains the main characteristics of the mission.


It is not possible to have simultaneously the two masses in free fall, because their orbits are very similar but not exactly identical. This is why one uses one of the two masses as a reference, whereas the other one is left free. It is on this second mass that one checks that it is in free fall, at least in the limits required for the acceleration noise.


“The measurements have exceeded our most optimistic expectations,” says Paul McNamara, LISA Pathfinder Project Scientist. “We reached the level of precision originally required for LISA Pathfinder within the first day, and so we spent the following weeks improving the results a factor of five better.”

Indeed, as shown on the following plot which appears in the published paper, the acceleration noise reached is 5 times smaller than what was required, basically it is already what is needed for the LISA mission, and even better for high frequencies.


“Not only do we see the test masses as almost motionless, but we have identified, with unprecedented precision, most of the remaining tiny forces disturbing them,” explains Stefano Vitale, the scientist in charge of the mission (Principal Investigator).

This success is obviously a green light for the gravitational wave observatory, the third large mission (L3) of the European Space Agency, known as LISA. This mission was originally identified for a launch in 2034 but this success, and the historic discovery of gravitational waves by the LIGO detector, offer strong arguments to advance significantly the schedule.


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