Cases & Voices
- María José López Pourailly
Enrique Zas, physicist: "It is an event that marks the beginning of a new form of observation"
Member and representative of Spain at the Pierre Auger Observatory, and Professor of the Galician Institute of High Energy Physics of the Department of Particle Physics of the Faculty of Physics at the University of Santiago de Compostela, Enrique Zas shared with us his experience in the process of observation of the fusion of two neutron stars recorded on Aug. 17, which he referres as an experience that changed the lives of the participating scientists.
What was the participation of the Pierre Auger Observatory in the research that led to the capture of light and gravitational waves of the stellar explosion revealed a few days ago?
On August 17, 2017, at 14:40 Central European Time, a new phase for Physics begun. The two arms - of 4 km each - of the two detectors of LIGO in Hanford and Livingston (USA) detected a tiny and harmonious contraction and expansion of Space, due to the passage of a gravitational wave. This time the "song" of the binary system lasted almost two minutes, becoming progressively more acute until the moment of the collision. The gravitational wave could also be confirmed by the European detector of Virgo, in Pisa (Italy), which has just entered into operation, allowing a better delimitation of the direction in which it was produced.
They found it in the data after receiving a message from a gamma-ray detector on the FERMI satellite that had located an explosion of gamma rays from a region of the broad sky, without being able to pinpoint the direction of its origin. It was found that the explosion occurred 1.7 seconds after the end of the gravitational wave, due to two neutron stars that rotate approaching progressively and increasing their speed as they radiated energy, until colliding. The end of the gravitational wave corresponds to the collision that releases a great amount of energy in a relatively small volume, since the neutron stars have a mass slightly greater than the sun but a radius of only about 10 kilometers. The explosion of gamma rays occurred almost immediately.
An extensive search campaign was conducted on all types of telescopes and observatories, X-rays, ultraviolet, optical, infrared, radio waves and neutrinos. We are all interconnected to be able to look for signals when exceptional events like this occur. The optical telescopes allowed to locate with precision the galaxy in which the explosion took place, and hours later they detected a new optical source in the galaxy NGC 4993, about 130 million light years away.
The Pierre Auger Observatory and the ANTARES and IceCube neutrino detectors, which belong to this network of detectors, received the alert briefly after the detection and carried out a search among high-energy neutrino data. None of the three observed neutrinos from this direction. This is also important because the models that try to explain these events predict the existence of neutrinos of high energies, especially in a direction that is perpendicular to the plane of rotation of the stars in which a gigantic stream of very energetic particles is emitted. Not observing them allows us to conclude that this jet did not point towards the Earth.
The Pierre Auger Observatory searches for neutrinos by selecting squalls that arrive very steep. One of the most efficient ways to detect them is by looking for almost horizontal cascades that occur when neutrinos interact in the rock near the surface and a charged particle (a tau lepton) comes out almost parallel to the surface that disintegrates in the atmosphere producing a horizontal shower. It has to be very energetic for the shower to be large enough to be detected by the Observatory and, to detect neutrinos in this way. They have to be of a special type, tau neutrinos. Only these neutrinos produce the tau lepton (there are three types of neutrinos associated with the electron, the muon and the tau). Our detector differs and complements the other neutrino detectors in several aspects: in energy, because it is only sensitive to very energetic neutrinos; in sensitivity, because it is very efficient to detect tau neutrinos that come from directions of a few degrees below the horizon, yes, crossing hundreds of kilometers over the Earth!; Regarding the "flavour" or the neutrino type, because it allows to distinguish tau neutrinos, since they are the only ones that we can detect below the horizon, and, finally, in directionality, because we can reconstruct the direction of arrival with precision in around one or two degrees. The main disadvantage is that at every moment our detector is limited to specific directions.
We were very lucky. The neutron collision was right in the best position it could be to detect high-energy neutrinos, which was two degrees below the horizon! As we do not detect neutrinos, we established some limits, we say that there could not be a flow greater than a certain amount. As it was so well oriented, our result is at higher energies more restrictive than the best neutrino detector in the world - the IceCube - and, therefore, very relevant in this range of energies. The result highlights the effectiveness of our detector when it is well oriented to detect neutrinos. We must not forget that the Auger Observatory does not have as its main objective to detect neutrinos, therefore, this is an added value of the Observatory that can not be overlooked.
How was developed this collaborative research?
About a year ago we began to establish contacts with LIGO to sign a cooperation agreement, predicting that something like this could happen. Many other observatories that could contribute with information did the same. The agreement was signed this year and we began receiving detection alert releases throughout the summer. There were many alerts, but this was undoubtedly the most relevant. When we got it we started searching our database and found that there were no rains that we could assign to neutrinos coming from the direction of the collision.
Simultaneously, other observatories did the same and many of them detected light (optical, infrared and ultraviolet spectrum), X-rays and radio waves; others put quotas. What is important in this is that they started to observe this success from the beginning, because the process is very complex and, once the collision has taken place, it emits radiation that changes frequency as the hours and the weeks pass. This information is a huge step in knowledge, since we have never had the opportunity to observe such a singular and complex process from so many points of view. By combining all the information we can draw conclusions about the phenomenon much more accurately.
Many scientific articles were published almost simultaneously on October 16 of this year. Our participation has generated two articles, one that includes all the detectors that had observation success and what will be remembered historically as the birth of Multimessenger Astronomy, and a more specific one on the neutrino quota, which we published together with three neutrino detectors and the LIGO collaboration.
How was the experience of participating in a collective effort with such a great result?
It was a really stimulating experience that even affected our personal lives. Because it was August, the holiday month of some of those involved, the event eventually changed our planning. Another example is one of the doctoral students who conducted the neutrino quest. He was in the hospital during the event and had to work from there. It is important to note this: without the selfless dedication of those involved, this milestone would not be possible.
How important was the collaborative work and the existence of advanced academic networks for this discovery?
Clearly all this is only possible thanks to the Internet. We could not imagine any of this without this network. The data from our observatory are distributed over the network and I believe that this also happens for all observatories (there are more than 70 involved). The internet also plays a key role in facilitating the alerts we receive through the network. Without doubt, the Internet is already so integrated with the scientific community that we had no B plan if it failed. If that happened we would have to do everything over the phone, which would be much more difficult.
What is the transcendence of this episode to Science?
The detection of gravitational waves by LIGO is exceptional, since measuring the frequency with which they orbit the stars allows to deduce many questions about the process. Most likely they were two neutron stars spinning around each other, progressively approaching until they collide. Its density is of the order of hundreds of millions of tons per cubic centimeter and, in the collision, a great amount of energy was released in very little time. Then came the "fireworks" of every possible color that lasted weeks and were observed by more than 70 observatories. It is an exceptional event, never recorded, and happened only '130 million light-years, ten times closer than the black hole collisions recorded so far. LIGO's article was published in Physical Review Letters on October 16 and was announced at a press conference.
There has been an intense search campaign for multiple telescopes ranging from radio, infrared, optical, ultraviolet, X-ray and gamma rays, as well as three neutrino telescopes - ANTARES, IceCube and the Pierre Auger Observatory - which way themselves in this direction. Simultaneously, more than 100 articles have been published or submitted, many in journals such as Nature, Nature Astronomy, Science, Astrophysical Journal Letters, Physica Review Letters, containing detailed information on each of these observations. The number of publications reflects the enormous scientific impact of this discovery.
All of these combined observations are a unique and unprecedented source of information that allows us to delve deeper into our studies of these cataclysmic phenomena in an exceptional way, and therefore, entail enormous strides in science. For now we have confirmed that the origin of at least part of the short bursts of gamma rays is due to the collision of neutron stars, something that until now was only a hypothesis. This data is collected in an article published on October 16 in the Astrophysical Journal Letters, by the collaboration of all these observatories including the Pierre Auger Observatory, one of the three neutrino detectors. It is a gigantic joint effort of many experiments, involving astronomy, astrophysics, particle physics and the new field of gravitational waves giving rise to an exceptional discovery. Undoubtedly, it marks the beginning of a new form of observation that some have already begun to call "multimessenger astronomy".
Read More:
- Chronicle of a global collaboration: the fusion of two neutron stars, a hug of 130 million years
- “La persecusión de una KiloNova”, por Luis Núñez: https://halley.uis.edu.co/clases/lnunez/
- Dr. Kathy Vivas, Astronomer: "A new era is starting for Astronomy”
- LIGO publication: https://www.ligo.caltech.edu/page/press-release-gw170817
- Pierre Auger publication: https://www.auger.org/index.php/news/latest-news/the-pierre-auger-antares-and-icecube-observatories-team-up-for-a-search-of-neutrino-emission-from-the-binary-neutron-star-merger-gw170817
- Publicación de ESO: https://www.eso.org/public/chile/news/eso1733/
Member and representative of Spain at the Pierre Auger Observatory, and Professor of the Galician Institute of High Energy Physics of the Department of Particle Physics of the Faculty of Physics at the University of Santiago de Compostela, Enrique Zas shared with us his experience in the process of observation of the fusion of two neutron stars recorded on Aug. 17, which he referres as an experience that changed the lives of the participating scientists.
What was the participation of the Pierre Auger Observatory in the research that led to the capture of light and gravitational waves of the stellar explosion revealed a few days ago?
On August 17, 2017, at 14:40 Central European Time, a new phase for Physics begun. The two arms - of 4 km each - of the two detectors of LIGO in Hanford and Livingston (USA) detected a tiny and harmonious contraction and expansion of Space, due to the passage of a gravitational wave. This time the "song" of the binary system lasted almost two minutes, becoming progressively more acute until the moment of the collision. The gravitational wave could also be confirmed by the European detector of Virgo, in Pisa (Italy), which has just entered into operation, allowing a better delimitation of the direction in which it was produced.
They found it in the data after receiving a message from a gamma-ray detector on the FERMI satellite that had located an explosion of gamma rays from a region of the broad sky, without being able to pinpoint the direction of its origin. It was found that the explosion occurred 1.7 seconds after the end of the gravitational wave, due to two neutron stars that rotate approaching progressively and increasing their speed as they radiated energy, until colliding. The end of the gravitational wave corresponds to the collision that releases a great amount of energy in a relatively small volume, since the neutron stars have a mass slightly greater than the sun but a radius of only about 10 kilometers. The explosion of gamma rays occurred almost immediately.
An extensive search campaign was conducted on all types of telescopes and observatories, X-rays, ultraviolet, optical, infrared, radio waves and neutrinos. We are all interconnected to be able to look for signals when exceptional events like this occur. The optical telescopes allowed to locate with precision the galaxy in which the explosion took place, and hours later they detected a new optical source in the galaxy NGC 4993, about 130 million light years away.
The Pierre Auger Observatory and the ANTARES and IceCube neutrino detectors, which belong to this network of detectors, received the alert briefly after the detection and carried out a search among high-energy neutrino data. None of the three observed neutrinos from this direction. This is also important because the models that try to explain these events predict the existence of neutrinos of high energies, especially in a direction that is perpendicular to the plane of rotation of the stars in which a gigantic stream of very energetic particles is emitted. Not observing them allows us to conclude that this jet did not point towards the Earth.
The Pierre Auger Observatory searches for neutrinos by selecting squalls that arrive very steep. One of the most efficient ways to detect them is by looking for almost horizontal cascades that occur when neutrinos interact in the rock near the surface and a charged particle (a tau lepton) comes out almost parallel to the surface that disintegrates in the atmosphere producing a horizontal shower. It has to be very energetic for the shower to be large enough to be detected by the Observatory and, to detect neutrinos in this way. They have to be of a special type, tau neutrinos. Only these neutrinos produce the tau lepton (there are three types of neutrinos associated with the electron, the muon and the tau). Our detector differs and complements the other neutrino detectors in several aspects: in energy, because it is only sensitive to very energetic neutrinos; in sensitivity, because it is very efficient to detect tau neutrinos that come from directions of a few degrees below the horizon, yes, crossing hundreds of kilometers over the Earth!; Regarding the "flavour" or the neutrino type, because it allows to distinguish tau neutrinos, since they are the only ones that we can detect below the horizon, and, finally, in directionality, because we can reconstruct the direction of arrival with precision in around one or two degrees. The main disadvantage is that at every moment our detector is limited to specific directions.
We were very lucky. The neutron collision was right in the best position it could be to detect high-energy neutrinos, which was two degrees below the horizon! As we do not detect neutrinos, we established some limits, we say that there could not be a flow greater than a certain amount. As it was so well oriented, our result is at higher energies more restrictive than the best neutrino detector in the world - the IceCube - and, therefore, very relevant in this range of energies. The result highlights the effectiveness of our detector when it is well oriented to detect neutrinos. We must not forget that the Auger Observatory does not have as its main objective to detect neutrinos, therefore, this is an added value of the Observatory that can not be overlooked.
How was developed this collaborative research?
About a year ago we began to establish contacts with LIGO to sign a cooperation agreement, predicting that something like this could happen. Many other observatories that could contribute with information did the same. The agreement was signed this year and we began receiving detection alert releases throughout the summer. There were many alerts, but this was undoubtedly the most relevant. When we got it we started searching our database and found that there were no rains that we could assign to neutrinos coming from the direction of the collision.
Simultaneously, other observatories did the same and many of them detected light (optical, infrared and ultraviolet spectrum), X-rays and radio waves; others put quotas. What is important in this is that they started to observe this success from the beginning, because the process is very complex and, once the collision has taken place, it emits radiation that changes frequency as the hours and the weeks pass. This information is a huge step in knowledge, since we have never had the opportunity to observe such a singular and complex process from so many points of view. By combining all the information we can draw conclusions about the phenomenon much more accurately.
Many scientific articles were published almost simultaneously on October 16 of this year. Our participation has generated two articles, one that includes all the detectors that had observation success and what will be remembered historically as the birth of Multimessenger Astronomy, and a more specific one on the neutrino quota, which we published together with three neutrino detectors and the LIGO collaboration.
How was the experience of participating in a collective effort with such a great result?
It was a really stimulating experience that even affected our personal lives. Because it was August, the holiday month of some of those involved, the event eventually changed our planning. Another example is one of the doctoral students who conducted the neutrino quest. He was in the hospital during the event and had to work from there. It is important to note this: without the selfless dedication of those involved, this milestone would not be possible.
How important was the collaborative work and the existence of advanced academic networks for this discovery?
Clearly all this is only possible thanks to the Internet. We could not imagine any of this without this network. The data from our observatory are distributed over the network and I believe that this also happens for all observatories (there are more than 70 involved). The internet also plays a key role in facilitating the alerts we receive through the network. Without doubt, the Internet is already so integrated with the scientific community that we had no B plan if it failed. If that happened we would have to do everything over the phone, which would be much more difficult.
What is the transcendence of this episode to Science?
The detection of gravitational waves by LIGO is exceptional, since measuring the frequency with which they orbit the stars allows to deduce many questions about the process. Most likely they were two neutron stars spinning around each other, progressively approaching until they collide. Its density is of the order of hundreds of millions of tons per cubic centimeter and, in the collision, a great amount of energy was released in very little time. Then came the "fireworks" of every possible color that lasted weeks and were observed by more than 70 observatories. It is an exceptional event, never recorded, and happened only '130 million light-years, ten times closer than the black hole collisions recorded so far. LIGO's article was published in Physical Review Letters on October 16 and was announced at a press conference.
There has been an intense search campaign for multiple telescopes ranging from radio, infrared, optical, ultraviolet, X-ray and gamma rays, as well as three neutrino telescopes - ANTARES, IceCube and the Pierre Auger Observatory - which way themselves in this direction. Simultaneously, more than 100 articles have been published or submitted, many in journals such as Nature, Nature Astronomy, Science, Astrophysical Journal Letters, Physica Review Letters, containing detailed information on each of these observations. The number of publications reflects the enormous scientific impact of this discovery.
All of these combined observations are a unique and unprecedented source of information that allows us to delve deeper into our studies of these cataclysmic phenomena in an exceptional way, and therefore, entail enormous strides in science. For now we have confirmed that the origin of at least part of the short bursts of gamma rays is due to the collision of neutron stars, something that until now was only a hypothesis. This data is collected in an article published on October 16 in the Astrophysical Journal Letters, by the collaboration of all these observatories including the Pierre Auger Observatory, one of the three neutrino detectors. It is a gigantic joint effort of many experiments, involving astronomy, astrophysics, particle physics and the new field of gravitational waves giving rise to an exceptional discovery. Undoubtedly, it marks the beginning of a new form of observation that some have already begun to call "multimessenger astronomy".
