19/03/2016: A “power house” at the Milky Way centre accelerates PeV protons

An international team of scientists, including David Berge, Jacco Vink, David Salek, Rachel Simoni and Mark Bryan at GRAPPA (University of Amsterdam), has discovered a source accelerating Galactic cosmic rays to energies never observed before in the Milky Way. The researchers suspect that the black hole at the centre of our galaxy can be held responsible. The findings of the scientists, united in the H.E.S.S. collaboration, were published in Nature on 16 March.

For over thirty years a collaboration of 42 institutes in 12 countries, including scientists of the UvA GRAPPA, Anton Pannekoek Institute for Astronomy, and the Institute of Physics, has been mapping the centre of our galaxy in very-high-energy gamma rays. A detailed analysis of the latest data reveals for the first time a source of this cosmic radiation at energies never observed before in the Milky Way: the supermassive black hole at its centre.

Cosmic rays

The Earth is constantly bombarded by high-energy particles (protons, electrons and atomic nuclei) of cosmic origin, particles that comprise the so-called “cosmic radiation”. Since more than a century, the origin of these cosmic rays remains one of the most enduring mysteries of science. The particles, such as protons, electrons and atomic nuclei are electrically charged, and are hence strongly deflected by the interstellar magnetic fields that pervade our galaxy. Fortunately, cosmic rays interact with light and gas in the neighbourhood of their sources and thereby produce gamma rays. These gamma rays travel in straight lines, undeflected by magnetic fields, and can therefore be traced back to their origin.

The source of gamma rays

Researchers of the High Energy Stereoscopic System-consortium (H.E.S.S.-consortium) used their telescopes in Namibia for the measurement. Ten years ago, they had already uncovered a very powerful point source of gamma rays in the galactic centre region, but the nature of the source remained a mystery. Possible objects capable of producing cosmic rays of high energy were supernova remnant, a pulsar wind nebula, and a compact cluster of massive stars.

Deeper observations made it now possible to pinpoint the black hole at the centre of the Milky Way as the source of the particles. This cosmic accelerator is about 100 times as powerful as the LHC at CERN, the largest terrestrial particle accelerator. The black hole is the first discovery of an astrophysical source capable of accelerating protons to energies of about one petaelectronvolt.


Artist’s impression of the giant molecular clouds surrounding the Galactic Centre, bombarded by very high energy protons accelerated in the vicinity of the central black hole and subsequently shining in gamma rays. © Dr Mark A. Garlick/ HESS Collaboration

The scientists have published their findings on 16 March in the journal Nature. Jacco Vink, David Berge, David Salek, Rachel Simoni and Mark Bryan have contributed to the research. Berge, the coordinator of the galactic science program of H.E.S.S., says: “It is great that we as a team finally found the source of gamma rays in the galactic centre region, after years of measuring and modelling.”

– Publication details: H.E.S.S. collaboration, corresponding authors: F. Aharonian, S. Gabici, E. Moulin and A. Viana; “Acceleration of petaelectronvolt protons in the Galactic Centre” Nature, 16 March 2016.

02/03/2016: NWO-M grant for David Berge

The CTA group around David Berge at the University of Amsterdam received a NWO-M grant (http://www.nwo.nl/en/funding/our-funding-instruments/nwo/investment-grant-nwo-medium/index.html) worth 356k Euro to build the core of the Clock Distribution and Trigger time Stamping (CDTS) system, the precision timing backbone, for CTA. CTA, The Cherenkov Telescope Array (https://www.cta-observatory.org) is one of the major future facilities of the field of astroparticle physics and high-energy astrophysics, dedicated to exploring the high-energy universe with gamma rays. Planned to start full operation in the early 2020’s, it will address important scientific topics, such as the origin of cosmic rays and their interaction with their environment, the energetic output of accreting black holes and the existence of dark matter.

The video below is an animation of what the telescope is to look like when finished.

CTA will be an observatory with arrays of telescopes on two sites, one in Spain on the Canary Island of La Palma for the Northern hemisphere, one at the European Southern Observatory (ESO) in Paranal in Chile for the Southern hemisphere, with 100 and 20 telescopes in the South and North, respectively.

CTA employs the Imaging Atmospheric Cherenkov Technique to measure cosmic gamma rays by recording the 10-ns long Cherenkov light flashes emitted in air showers induced by these gamma rays in the Earth’s atmosphere. Precise nanosecond timing is therefore mandatory for CTA to correctly tag and identify these short light flashes in the various telescopes.

The CDTS system that dr. Berge is working on, including a common timing card in every telescope, is based on “White Rabbit” (http://www.ohwr.org/projects/white-rabbit/wiki). This is an extension of the Ethernet protocol that distributes timing signals with nanosecond precision in optical networks.

17/02/2016: Vici grant for Sera Markoff

Congratulations to Dr Sera Markoff, Associate Professor at the UvA Anton Pannekoek Institute for Astronomy and a GRAPPA memberhe GRAPPA Center of Excellence. She was awarded a prestigious Vici grant. Markoff receives the grant for her project entitled “From micro- to megascales: understanding how black holes shape the local universe”.


This is primarily a theoretical project, focusing on the very important role black holes play in “recycling” material and subsequently energising their surroundings. Although black holes are famous for sucking up everything in their paths, including light, in reality they manage to convert captured material into other forms with an efficiency that can be orders of magnitude larger than nuclear fusion.

Jets – The most dramatic outputs are immense streams of magnetised plasma moving at near light speed, called jets. Jets from a supermassive black hole like the one in the centre of our Galaxy (luckily not currently ‘active’) can dump the energy equivalent of 100 billion supernovae into their environment, heating the surrounding gas to the point where it cannot collapse to form stars and effectively halting future galaxy growth. The myriad small, stellar-remnant black holes in every galaxy also enact a ‘micro’ version of this feedback, locally affecting star formation. At the moment there is no predictive theory for how this fundamental process occurs. At the same time several new observatories are just about to come online, that will deliver incredibly precise data from thousands of newly discovered black holes, and even make images of (some of) their Event Horizons.

A picture from the X-ray satellites Chandra (NASA) and XMM-Newton (ESA) showing the hot gas trapped in a cluster of galaxies
Image: combined X-ray image from NASA/ESA satellites Chandra and XMM-Newton showing the hot gas trapped within a cluster of galaxies.The image is almost a million light years across, the bright central spot is a galaxy, buried inside is a supermassive black hole that has launched immense jets 100s of millions of times larger than itself, which have inflated symmetric ‘bubbles’ on either side.  Each bubble is many times larger than our Galaxy, and older sets of bubbles show that this process has been driving pressure waves and even weak shocks for millions of years, disrupting and heating the gas on massive scales. Markoff and collaborators seek to understand this process. Credits: NASA.


Research Team – Sera Markoff will use the Vici grant to build a research group of three PhD students and two postdocs to tackle this problem. They will use existing HPC facilities as well as building a local compute cluster to develop models that can be tested against the new, precision observations across the electromagnetic spectrum. There are strong links to astroparticle physics, because Markoff and group will test also against signals from particles like high-energy cosmic rays and now even gravitational waves from merging compact objects.

Finally, Markoff has a project that will focus on science outreach in the Indishe Buurt in Amsterdam, as well as in number of refugee centers.

12/02/2016: Gravitational Waves detected!

ligo20160211_TnFor the first time, scientists have observed ripples in the fabric of spacetime called gravitational waves, arriving at the earth from a cataclysmic event in the distant universe. This confirms a major prediction of Albert Einstein’s 1915 general theory of relativity and opens an unprecedented new window onto the cosmos.

Gravitational waves carry information about their dramatic origins and about the nature of gravity that cannot otherwise be obtained. Physicists have concluded that the detected gravitational waves were produced during the final fraction of a second of the merger of two black holes to produce a single, more massive spinning black hole. This collision of two black holes had been predicted but never observed.

The gravitational waves were detected on September 14, 2015 at 5:51 a.m. Eastern Daylight Time (09:51 UTC) by both of the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, USA. The LIGO Observatories are funded by the National Science Foundation (NSF), and were conceived, built, and are operated by Caltech and MIT. The discovery, accepted for publication in the journal Physical Review Letters, was made by the LIGO Scientific Collaboration (which includes the GEO Collaboration and the Australian Consortium for Interferometric Gravitational Astronomy) and the Virgo Collaboration using data from the two LIGO detectors.

Based on the observed signals, LIGO scientists estimate that the black holes for this event were about 29 and 36 times the mass of the sun, and the event took place 1.3 billion years ago. About 3 times the mass of the sun was converted into gravitational waves in a fraction of a second—with a peak power output about 50 times that of the whole visible universe. By looking at the time of arrival of the signals—the detector in Livingston recorded the event 7 milliseconds before the detector in Hanford—scientists can say that the source was located in the Southern Hemisphere.

According to general relativity, a pair of black holes orbiting around each other lose energy through the emission of gravitational waves, causing them to gradually approach each other over billions of years, and then much more quickly in the final minutes. During the final fraction of a second, the two black holes collide into each other at nearly one-half the speed of light and form a single more massive black hole, converting a portion of the combined black holes’ mass to energy, according to Einstein’s formula E=mc2. This energy is emitted as a final strong burst of gravitational waves. It is these gravitational waves that LIGO has observed.

The existence of gravitational waves was first demonstrated in the 1970s and 80s by Joseph Taylor, Jr., and colleagues. Taylor and Russell Hulse discovered in 1974 a binary system composed of a pulsar in orbit around a neutron star. Taylor and Joel M. Weisberg in 1982 found that the orbit of the pulsar was slowly shrinking over time because of the release of energy in the form of gravitational waves. For discovering the pulsar and showing that it would make possible this particular gravitational wave measurement, Hulse and Taylor were awarded the Nobel Prize in Physics in 1993.

The new LIGO discovery is the first observation of gravitational waves themselves, made by measuring the tiny disturbances the waves make to space and time as they pass through the earth.

“Our observation of gravitational waves accomplishes an ambitious goal set out over 5 decades ago to directly detect this elusive phenomenon and better understand the universe, and, fittingly, fulfills Einstein’s legacy on the 100th anniversary of his general theory of relativity,” says Caltech’s David H. Reitze, executive director of the LIGO Laboratory.

The discovery was made possible by the enhanced capabilities of Advanced LIGO, a major upgrade that increases the sensitivity of the instruments compared to the first generation LIGO detectors, enabling a large increase in the volume of the universe probed—and the discovery of gravitational waves during its first observation run. The US National Science Foundation leads in financial support for Advanced LIGO. Funding organizations in Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council, STFC) and Australia (Australian Research Council) also have made significant commitments to the project. Several of the key technologies that made Advanced LIGO so much more sensitive have been developed and tested by the German UK GEO collaboration. Significant computer resources have been contributed by the AEI Hannover Atlas Cluster, the LIGO Laboratory, Syracuse University, and the University of Wisconsin- Milwaukee. Several universities designed, built, and tested key components for Advanced LIGO: The Australian National University, the University of Adelaide, the University of Florida, Stanford University, Columbia University of the City of New York, and Louisiana State University.

“In 1992, when LIGO’s initial funding was approved, it represented the biggest investment the NSF had ever made,” says France Córdova, NSF director. “It was a big risk. But the National Science Foundation is the agency that takes these kinds of risks. We support fundamental science and engineering at a point in the road to discovery where that path is anything but clear. We fund trailblazers. It’s why the U.S. continues to be a global leader in advancing knowledge.”

LIGO research is carried out by the LIGO Scientific Collaboration (LSC), a group of more than 1000 scientists from universities around the United States and in 14 other countries. More than 90 universities and research institutes in the LSC develop detector technology and analyze data; approximately 250 students are strong contributing members of the collaboration. The LSC detector network includes the LIGO interferometers and the GEO600 detector. The GEO team includes scientists at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute, AEI), Leibniz Universität Hannover, along with partners at the University of Glasgow, Cardiff University, the University of Birmingham, other universities in the United Kingdom, and the University of the Balearic Islands in Spain.

“This detection is the beginning of a new era: The field of gravitational wave astronomy is now a reality,” says Gabriela González, LSC spokesperson and professor of physics and astronomy at Louisiana State University.

LIGO was originally proposed as a means of detecting these gravitational waves in the 1980s by Rainer Weiss, professor of physics, emeritus, from MIT; Kip Thorne, Caltech’s Richard P. Feynman Professor of Theoretical Physics, emeritus; and Ronald Drever, professor of physics, emeritus, also from Caltech.

“The description of this observation is beautifully described in the Einstein theory of general relativity formulated 100 years ago and comprises the first test of the theory in strong gravitation. It would have been wonderful to watch Einstein’s face had we been able to tell him,” says Weiss.

“With this discovery, we humans are embarking on a marvelous new quest: the quest to explore the warped side of the universe—objects and phenomena that are made from warped spacetime. Colliding black holes and gravitational waves are our first beautiful examples,” says Thorne.

Virgo research is carried out by the Virgo Collaboration, consisting of more than 250 physicists and engineers belonging to 19 different European research groups: 6 from Centre National de la Recherche Scientifique (CNRS) in France; 8 from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; 2 in The Netherlands with Nikhef; the Wigner RCP in Hungary; the POLGRAW group in Poland; and the European Gravitational Observatory (EGO), the laboratory hosting the Virgo detector near Pisa in Italy.

Fulvio Ricci, Virgo Spokesperson, notes that, “This is a significant milestone for physics, but more importantly merely the start of many new and exciting astrophysical discoveries to come with LIGO and Virgo.”

Bruce Allen, managing director of the Max Planck Institute for Gravitational Physics (Albert Einstein Institute), adds, “Einstein thought gravitational waves were too weak to detect, and didn’t believe in black holes. But I don’t think he’d have minded being wrong!”

“The Advanced LIGO detectors are a tour de force of science and technology, made possible by a truly exceptional international team of technicians, engineers, and scientists,” says David Shoemaker of MIT, the project leader for Advanced LIGO. “We are very proud that we finished this NSF-funded project on time and on budget.”

At each observatory, the two-and-a-half-mile (4-km) long L-shaped LIGO interferometer uses laser light split into two beams that travel back and forth down the arms (four-foot diameter tubes kept under a near-perfect vacuum). The beams are used to monitor the distance between mirrors precisely positioned at the ends of the arms. According to Einstein’s theory, the distance between the mirrors will change by an infinitesimal amount when a gravitational wave passes by the detector. A change in the lengths of the arms smaller than one-ten-thousandth the diameter of a proton (10-19 meter) can be detected.

“To make this fantastic milestone possible took a global collaboration of scientists—laser and suspension technology developed for our GEO600 detector was used to help make Advanced LIGO the most sophisticated gravitational wave detector ever created,” says Sheila Rowan, professor of physics and astronomy at the University of Glasgow.

Independent and widely separated observatories are necessary to determine the direction of the event causing the gravitational waves, and also to verify that the signals come from space and are not from some other local phenomenon.

Toward this end, the LIGO Laboratory is working closely with scientists in India at the Inter-University Centre for Astronomy and Astrophysics, the Raja Ramanna Centre for Advanced Technology, and the Institute for Plasma to establish a third Advanced LIGO detector on the Indian subcontinent. Awaiting approval by the government of India, it could be operational early in the next decade. The additional detector will greatly improve the ability of the global detector network to localize gravitational-wave sources.

“Hopefully this first observation will accelerate the construction of a global network of detectors to enable accurate source location in the era of multi-messenger astronomy,” says David McClelland, professor of physics and director of the Centre for Gravitational Physics at the Australian National University.

Additional video and image assets can be found here: http://mediaassets.caltech.edu/gwave

04/02/2016: Millisecond pulsars may explain Galactic center gamma-ray excess

The puzzling excess of gamma rays from the centre of the Milky Way probably originate from rapidly rotating neutron stars, or millisecond pulsars, and not from dark matter annihilation, as previously claimed. This is the conclusion of new data analyses by two independent research teams from the University of Amsterdam (UvA) and Princeton University/Massachusetts Institute of Technology. The researchers’ findings were published on Thursday, 4 February in Physical Review Letters.

In 2009 observations with the Fermi Large Area Telescope revealed an excess of high-energetic photons, or gamma rays, around 2 GeV (gigaelectronvolt) at the centre of our Galaxy. It was long speculated that this gamma ray excess could be a signal of dark matter annihilation. If true, it would constitute a breakthrough in fundamental physics and a major step forward in our understanding of the matter constituents of the universe.
However, many other hypotheses have emerged in recent years, suggesting the gamma ray excess in the centre of our Galaxy might have a more ordinary, astrophysical cause. Possible origins for the observed gamma ray excess range from the activity of the supermassive black hole in the centre of our Milky Way and star formation in the central molecular zone to the combined emission of a new dim source population in the galactic bulge.

Millisecond pulsars
New statistical analyses of the Fermi data by Dr Christoph Weniger, assistant professor at the UvA, and a research group from Princeton/MIT, now strongly suggest that the excess emission does indeed originate from unresolved point sources. The best candidates are millisecond pulsars, the researchers conclude.
Millisecond pulsars, or rapidly rotating neutron stars, were often formed billions of years ago. They are among the most extreme objects in the Galaxy. A population of hundreds or thousands of these millisecond pulsars must be lurking in the galactic centre, hidden from detection due to present day instrument sensitivity. Future radio surveys with existing and upcoming telescopes (e.g. Green Bank Telescope, Square Kilometre Array) will be able to further test this hypothesis in the coming years.

Gamma ray picture of the Milky Way, as seen by the NASA Fermi satellite. Inserts: two independent statistical analyses showed that the distribution of photons is clumpy rather than smooth, indicating that the excess gamma rays from the centre of our galaxy are unlikely to be caused by dark matter annihilation.


Image courtesy of Christoph Weniger, UvA , © UvA/Princeton

Win-win situation
In their analyses, the UvA and Princeton/MIT researchers each used a different statistical technique, ‘non-Poissonian noise’ and ‘wavelet transformation’, to analyse the Fermi data. What they found was that the distribution of photons was clumpy rather than smooth, indicating that the gamma rays were unlikely to be caused by dark matter particle collisions.

According to Weniger, lead author of one of the papers, this is a win-win situation. ‘Either we find hundreds or thousands of millisecond pulsars in the upcoming decade, shedding light on the history of the Milky Way, or we find nothing. In the latter case, a dark matter explanation for the gamma ray excess will become much more obvious.’

Mariangela Lisanti, assistant professor at Princeton University and one of the authors of the second paper, adds: ‘The results of our analysis probably mean that what we are seeing is evidence for a new population of astrophysical sources in the centre of the Galaxy. That in itself is something new and surprising.’

Publication details:
Richard Bartels, Suraj Krishnamurthy and Christoph Weniger: ‘Strong support for the millisecond pulsar origin of the Galactic center GeV excess’ in: Physical Review Letters, (February 4, 2016). http://arxiv.org/abs/1506.05104

Samuel K. Lee, Mariangela Lisanti, Benjamin R. Safdi, Tracy R. Slatyer and Wei Xue: ‘Evidence for Unresolved Gamma-Ray Point Sources in the Inner Galaxy’ in: Physical Review Letters, February 4, 2016, http://arxiv.org/abs/1506.05124


03/02/2016: Letter of Intent for KM3NeT 2.0

Scientists of the KM3NeT Collaboration have publicly announced KM3NeT 2.0, their ambition for the immediate future to further exploit the clear waters of the deep Mediterranean Sea for the detection of cosmic and atmospheric neutrinos. The published Letter of Intent details the science performance as well as the technical design of the KM3NeT 2.0 infrastructure.

km3net-geometry-cylinder-exampleThe two major scientific goals of KM3NeT 2.0 are the discovery of astrophysical sources of neutrinos in the Universe with the KM3NeT/ARCA detector and the measurement of the neutrino mass hierarchy using atmospheric neutrinos with the KM3NeT/ORCA detector. Thanks to the flexible KM3NeT design, efficient detection of neutrinos is possible over a wide energy range (GeV to PeV) with an almost identical implementation. The KM3NeT scientists estimate that with the ARCA detector installed at the KM3NeT-It site south of Sicily, Italy, the observation of the cosmic neutrino flux reported by the IceCube Collaboration will be possible within one year of operation. With the ORCA detector installed at the KM3NeT-Fr site south of Toulon, France, they expect to determine neutrino mass hierarchy with at least 3-sigma significance after three years of operation.

Rosa Coniglione, KM3NeT Workgroup leader HE Astrophysics: ”The combination of the cost effective design of the ARCA detector of KM3NeT and state-of-the-art reconstruction software allows for efficient detection of all three neutrino flavours from cosmic origin in a few years.”

Antoine Kouchner, KM3NeT Workgroup leader LE Physics: “With the densely instrumented ORCA detector of KM3NeT we will be able to determine the relative ordering of the neutrino masses, also referred to as the neutrino mass hierarchy.”

The Letter of Intent is now open for scrutiny by the neutrino scientific community and will serve as the reference document for requests for funding by the various stakeholders in Europe and abroad. Pending funding, KM3NeT 2.0 could become reality as early as in 2020.

Uli Katz, KM3NeT Physics and Software manager: “The modular design of KM3NeT with detector blocks for the telescope makes it possible to swiftly react on new scientific developments. With KM3NeT 2.0 we are able to not only perform all-flavour neutrino astroparticle physics but also advance fundamental neutrino particle physics.”

Reference: Letter of Intent for KM3NeT 2.0, arXiv:1601.07459

11/01/2016: GRAPPA will host “DM @ LHC” and the “2nd Anisotopic Universe” workshops

The GRAPPA Institute will host two exiting workshops in March/April.

The 3rd “Dark Matter at the Large Hadron Collider” workshop will be held from 30 March to 1 April 2016 jointly by GRAPPA and Nikhef. The aim of the workshop is to bring together the leading experts in the field of Dark Matter searches in order to review the latest results from both theory and the experiments, especially in the light of the new results from the 2015 LHC data sets.

The 2nd Anisotropic Universe workshop “Unveiling the Anisotropic Universe” will be held from 11 to 13 April 2016 with the aim to exploit the momentum recently gained by the cross-field topic of anisotropies to launch a collaborative effort to unravel fundamental issues in astrophysics and cosmology as, for example, the origin of ultra-high energy cosmic rays and neutrinos, and the nature of dark matter.

Register and stay tuned!

08/12/2015: Gamma-ray Cherenkov Telescope prototype inaugurated on 1 December 2015

The inauguration of the Gamma-ray Cherenkov Telescope (GCT) prototype on 1 December 2015 was hosted by l’Observatoire de Paris. The GCT will detect very high-energy gamma rays for the world’s largest gamma ray observatory: the Cherenkov Telescope Array (CTA). GRAPPA and the Anton Pannekoek Institute for Astronomy are among the major contributors to the development of the camera for the GCT.


CTA will consist of an array of many telescopes that will be used to make images of gamma-ray sources, such as remnants of supernova explosions, and matter swallowing black holes. The gamma-ray radiation cannot be detected directly, but gamma rays entering the atmosphere will cause a track of bluish light that can be detected by optical telescopes. By combining observations of many telescopes, the trajectory of the gamma-ray light can be reconstructed and images of the high energy sources can be obtained.

The inauguration of the prototype GCT on 1 December was held at the Observatory’s Meudon site with speeches and presentations by representatives from l’Observatoire de Paris, Centre National de la Recherche Scientifique (CNRS), Science and Technology Facilities Council (STFC), Region Ile-de-France, the CTA and GCT consortia.

The telescope is one of the very first to use the Schwarzschild-Couder dual-mirror optical design, which has recently been recognized as well-suited to ground-based gamma-ray astronomy, providing good image quality over a large field of view and allowing the construction of telescopes and cameras that are more compact than the single-mirror systems that are currently in use.

The GCT is one of CTA’s small size telescopes (SSTs) and will cover the high end of the CTA energy range, between about 1 and 300 TeV (tera-electronvolts). Around 70 SSTs are needed to make sure CTA is sufficiently sensitive at these enormous energies. The GCT is one of three different SST implementations being prototyped and tested around the world. Current expectations are that the array will include approximately 35 GCTs.

They will be built by an international collaboration with contributions from institutes and universities in Australia, France, Germany, Japan, the Netherlands and the United Kingdom.

[Photos by Akira Okumura]

18/11/2015: XENON1T inaugurated at Gran Sasso laboratory

An international collaboration of scientists, with GRAPPA member Patrick Decowski and his team, inaugurated the new XENON1T experiment in the underground Gran Sasso laboratory in Italy. It is designed to search with an unprecedented sensitivity for dark matter, one of the main ingredients of the Universe.

XENON1T is located in the Laboratori Nazionali del Gran Sasso in Italy, one of the largest underground laboratories in the world. “We perform our experiment in a water tank, 1400 meter underground, because we want to detect only dark matter, and filter out all other types of radiation. The massive layer of rock and the water shield off the sensitive equipment” says Decowski.


It took 20 research groups from 10 countries five years to complete the experiment. As soon as XENON1T is fully operational, it will take about a week for the experiment to become the most sensitive dark matter experiment in the world. With a total mass of 3500 kg it is the third generation of instruments in the XENON project that started 15 years ago. XENON1T is named after the noble gas xenon, with which the detector is filled. A collision of dark matter with xenon would result in a tiny flash of light. 248 extremely sensitive light sensors will be searching for such flashes. The first results are expected early 2016.

16/11/2015: Patrick Decowski among awardees of 2016 Breakthrough Prizes

The 2016 Breakthrough Prize in Fundamental Physics was awarded to five experiments investigating neutrino oscillation and will be shared equally among all five. GRAPPA member Patrick Decowski is among the awardees, as a team member of the KamLAND collaboration in Japan.


To all teams involved (and their combined 1,377 team leaders and members) the award is presented for the fundamental discovery and exploration of neutrino oscillations, revealing a new frontier beyond, and possibly far beyond, the standard model of particle physics. Decowski, now program leader of the Dark Matter research program of Nikhef, has been working since 2002 in the Japanese Alps on the KamLAND experiment, which has revealed and precisely measured a number of previously unknown neutrino properties, such as the neutrino oscillations now leading to the Breakthrough Prize.

Apart from the KamLAND collaboration, the awarded teams include Daya Bay (China); K2K / T2K (Japan); Sudbury Neutrino Observatory (Canada); and Super-Kamiokande (Japan).

30/10/2015: Book Prize for G. Bertone’s “Behind the Scenes of the Universe”

CQUweh3XAAICVoxThe French edition of the popular science book “Behind the Scenes of the Universe: from the Higgs to Dark Matter”, published by Dunod, has won the “Ciel et Espace” prize for the best astronomy book. Here’s the motivation, translated from French:

The scientific investigation proposed by Gianfranco Bertone in« Le mystère de la matière noire » captivated  the judging panel, who appreciated the quality of his popularization work  […]« Le mystère de la matière noire » tells with lively and entertaining language the discoveries that led scientists to postulate the existence of a new form of matter. This book plunged the reader behind the scenes of modern scientific research: methods, hopes, failures, of the searches performed by scientists.

26/10/2015: New GRAPPA Members

New post-docs and graduate students recently joined the GRAPPA institute which now includes 7 faculty members, 16 post-docs, 17 graduate students and several associated faculty members from API, Nikhef and the Institute of Physics.

Check out our full list of members!

18/08/2015: “Gamma Rays & Dark Matter” workshop on 7-11 December 2015

The workshop “Gamma Rays and Dark Matter“, organized by David Berge from GRAPPA and other colleagues, will take place from 7 to 11 December in Obergurgl in the Austrian Alps.

The event is focused on high and very high energy gamma ray measurements over large angular scales and in particular their relevance for indirect dark matter searches. The workshop will gather world-leading experts of dark matter phenomenology, dark matter searches in gamma rays, in high-energy astrophysics processes that produce gamma rays, and experimental aspects of gamma ray measurements in general. We will have focused discussions bridging across different fields, and we will develop new synergetic ideas and future strategies in the search for dark matter shining in gamma rays.

2015-08-18 12.18.55 pm

29/07/2015: Paranal and La Palma sites chosen for the Cherenkov Telescope Array

On 15 and 16 July 2015, the Cherenkov Telescope Array (CTA) Resource Board decided to enter into detailed contract negotiations for hosting CTA on the European Southern Observatory (ESO) Paranal grounds in Chile and at the Instituto de Astrofisica de Canarias (IAC), Roque de los Muchachos Observatory in La Palma, Spain.

This is a big step forward for the future of ground-based gamma-ray astronomy represented by the CTA observatory and several GRAPPA members are involved in this project.

The full CTA press release can be found here and downloaded here.


29/07/2015: 34th International Cosmic Ray Conference in The Hague

The Netherlands is hosting the 34th International Cosmic Ray Conference (ICRC) starting tomorrow July 30 till August 6, 2015, in The Hague.

The ICRC an important and large conference in the field of Astroparticle Physics covering cosmic-ray physics, solar and heliospheric physics, gamma-ray astronomy, neutrino astronomy, and dark matter physics.


14/04/2015: Patrick Decowski, professor of Experimental Astroparticle Physics

Congratulations to GRAPPA faculty member Dr M.P. Decowski who has been appointed professor of Experimental Astroparticle Physics at the University of Amsterdam’s (UvA) Faculty of Science.


Patrick Decowski conducts experimental research in the area of astroparticle physics, at the intersection of particle physics and astrophysics. His main current interests are the composition of dark matter and the properties of neutrinos. To conduct his research, he participates in experiments in deep underground labs in Italy and Japan. In the Italian Apennines, Decowski is working to unravel the particle composition of dark matter in the XENON project. Dark matter is an as-yet-unknown substance that constitutes over 85% of the universe’s mass. Decowski wants to observe dark matter particles colliding with ordinary matter and discover their properties using extremely sensitive liquid xenon detectors. In the near future, the XENON project will begin operating the XENON1T, the most sensitive dark matter detector on earth.

Since 2002, Decowski has also been working in the Japanese Alps on the KamLAND experiment, which has revealed and precisely measured a number of previously unknown neutrino properties, such as neutrino oscillations. The KamLAND detector is currently in a phase that aims to discover whether neutrinos could be their own antiparticles or ‘Majorana particles’ through a process known as neutrinoless double beta decay. If so, this would shed light on a number of areas, including the standard model of particle physics and cosmology. Dark matter particle collisions and neutrinoless double beta decays are extremely rare events and sensitive detectors constructed of very low radioactivity components are required.

Decowski has worked as an associate professor at the UvA since 2011. He obtained his PhD at the Massachusetts Institute of Technology (MIT), after which he was at the University of California, Berkeley for eight years. After returning to the Netherlands in 2009, he served as a senior scientist at the National Institute for Subatomic Physics (Nikhef). Still affiliated with Nikhef, Decowski is the programme leader of the Dark Matter research programme of the Foundation for Fundamental Research on Matter (FOM). He is also a visiting scientist at the Kavli Institute of the Physics and Mathematics of the Universe (IPMU) at the University of Tokyo. He has received various research grants, including grants from the FOM and the Netherlands Organisation for Scientific Research (NWO).

10/02/2015: First proof of dark matter in innermost region of Milky Way

An international team of researchers, which includes GRAPPA spokeperson Gianfranco Bertone, has obtained the first observational proof of the presence of dark matter in the innermost part of the Milky Way, where our own planet is located. Their results were published yesterday online in the journal “Nature Physics“.

The universe is pervaded by invisible dark matter, which is about five times more abundant than the “ordinary matter” comprised of atoms. Its existence in galaxies was established in the 1970s with a variety of techniques, including the measurement of the rotation speed of gas and stars, which provides a way to effectively “weigh” the host galaxy and determine its mass.


 This photograph of the Milky Way was taken from the Paranal Observatory in Chile’s Atacama Desert: John Colosimo (colosimophotography.com)/ESO.

Rotation Speed

This technique can also be applied to our own Galaxy. Although the existence of dark matter in the outer parts of the Milky Way is well established, it has historically proven very difficult to confirm the existence of dark matter within the innermost regions, where the solar system is located, due to the difficulty of measuring the rotation of gas and stars with the needed precision.

Bertone – with co-authors Fabio Iocco of the ICTP South American Institute for Fundamental Physics and Miguel Pato of Stockholm University – created the most complete compilation of published measurements of the motion of gas and stars in the Milky Way, and compared the measured rotation speed with that expected under the assumption that only luminous matter exists in the Galaxy. Their findings demonstrate that the observed rotation cannot be explained unless large amounts of dark matter exist around us, and between us and the galactic centre.

Gianfranco Bertone: “We anticipate that our results will lead to further developments in astroparticle physics and cosmology. With new upcoming astronomical observations, our method will allow us to measure the distribution of dark matter in our Galaxy with unprecedented precision. This will refine our understanding of the structure and evolution of our Galaxy, and it will trigger more robust predictions for the many experiments worldwide that search for dark matter particles. Our study therefore constitutes a fundamental step forward in the quest for the nature of dark matter.”

Pubblication Details. Fabio Iocco, Miguel Pato and Gianfranco Bertone, “Evidence for dark matter in the inner Milky Way“, Nature Physics (online publication 9 February). DOI: 10.1038/NPHYS3237

23/01/2015: Exceptionally powerful gamma-ray emitters in the Large Magellanic Cloud

The High Energy Stereoscopic System (H.E.S.S.) observed the Large Magellanic Cloud, a satellite galaxy of the Milky Way, for more than 200 hours. The impressive results of this observation have been published yesterday in Science, with an important contribution from Jacco Vink, part of the H.E.S.S. group at API-GRAPPA.



Three different type of sources have been detected at very-high gamma-ray energies: the superbubble 30DorC, the pulsar wind nebula N157B, and the supernova remnant N132D. This is the first time that such objects are unambiguously identified in gamma-rays beyond our own galaxy. The super bubble 30DorC is especially interesting as it is the first time gamma-rays from a superbubble have been detected.


13/01/2015: Debate “Dark Matter: a cosmic mystery” on January 22nd

On January 22nd, GRAPPA members Gianfranco Bertone, Nassim Bozorgnia and Christoph Weniger will present one of the main research lines of the GRAPPA institute in the public debate “Dark Matter: a cosmic mystery“.

The debate will stat at 17.00 and will be held at the Academische Club. The program will be the following:

  • Introduction to dark matter – Gianfranco Bertone
  • How do we search for something we know nothing about? – Christoph Weniger
  • How do we build an experiment to search for dark matter particles? – Nassim Bozorgnia
  • What happens if new particles are (not) discovered? – all
  • Q&A

More information about the program can be found here.

12/01/2015: New Dark Matter App

What is dark matter? The answer to this question – and a lot more information – can be found in the new app ‘Dark Matter – Behind the Scenes of the Universe’. Developed by UvA researcher Gianfranco Bertone, spokesperson of the GRAPPA research priority area, the app is available now on both iPhone and iPad.

The app is a follow-up to the book Behind the Scenes of the Universe: From the Higgs to Dark Matter (Bertone, Oxford University Press 2013). The text of this book is enriched with new visuals, videos and useful links within the fields of cosmology and astroparticle physics. Bertone: ‘The app allows to go beyond the limited possibilities offered by printed books. I wanted to explore ways of bringing science closer to society, especially students and young people…’

Bertone adds: ‘In collaboration with professional app developers in London, we started by designing a visually appealing interface. The result is an app that looks like a video game, reads like a popular science book and can be used as a portal to selected, high-quality science resources on the Internet.’

Available for download.

The app can be downloaded from the Apple App Store for both the iPhone and iPad. ‘The app is accessible to anyone. By navigating the app and the linked resources, students and young readers will learn about modern physics and cosmology, and the big open questions in science. More advanced readers will learn about the latest developments in the fields, including a description of the most recent experiments and the prospects for…future discoveries.’

In future, Bertone hopes to assist other scientists who would like to create similar apps. ‘We enjoyed developing this app and are collecting ideas for future projects.’

Click here to download the app.


20/11/2014: FOM grant for Ben Freivogel

Congratulations to GRAPPA faculty Ben Freivogel who has been awarded a “Projectruimte” FOM grant for his proposal “Quantifying violations of causality in quantum gravity”.

The award allows Freivogel to hire a PhD student and a Postdoc. Freivogel and his team will investigate in what situations the locality of physics may be violated, by studying aspects of quantum gravity.

The Projectruimte is one of the grant instruments that FOM has to fund physics research. The Projectruimte makes it possible to realise small-scale projects of fundamental research with an innovative character and a demonstrable scientific, industrial or societal urgency.

On 11 November 2014, the Executive Board of the FOM Foundation decided to award five proposals in the FOM-Projectruimte. A total of 2.3 million euros has been awarded to the projects.


13/10/2014: New GRAPPA Members

New post-docs and graduate students recently joined the GRAPPA institute which now includes 7 faculty members, 13 post-docs, 11 graduate students, with few more to come, and several associated faculty members from API, Nikhef and the Institute of Physics.

Check out our full list of members.

26/09/2014: Gianfranco Bertone appointed GRAPPA Spokesperson

Gianfranco Bertone has been appointed ‘GRAPPA Spokesperson’ by the GRAPPA Faculty council. He will be responsible for the coordination of a number of GRAPPA activities, including national and international collaborative research projects, grant submissions and hiring, as well as for institutional representation, and fund raising. 

The educational aspects of the GRAPPA MSc track will continue to be coordinated by Patrick Decowski.

29/07/2014: Veni grant for Fabio Zandanel

Congratulations to Fabio Zandanel, who has been awarded a NWO Veni grant for the project “Monsters Unveiled: Cosmic Rays and Dark Matter in Clusters of Galaxies”. In his own words:

“The Universe evolved from tiny fluctuations in an almost uniform density field. As matter surrounding these small over-densities collapsed due to gravitational force, the first stars formed. The latest and largest gravitationally bound structures to form are clusters of galaxies. The main goal of this project is to obtain a coherent picture of structure formation in clusters. These contain substantial amounts of cosmic rays (CRs) as well as dark matter (DM), a yet to be identified form of matter that dominates the Universe. My aim is to discover the connection between the CR population and acceleration processes generating diffuse synchrotron radio emission, called radio halos, and structure formation processes. Structure formation itself is mainly driven by the DM gravitational effect, thus DM identification, one of the most important goals of modern physics, is also crucial for the understanding of the evolutionary process.”