The top prize in high-energy astrophysics, the Bruno Rossi Prize 2020, has been awarded to the Event Horizon Telescope team for the landmark image and analysis of the first shadow of a black hole. The UvA-researchers Sera Markoff, Oliver Porth, Doosoon Yoon and Koushik Chatterjee are part of this team.
The American Astronomical Society awards the Rossi Prize in recognition of significant contributions as well as recent and original work in high-energy astrophysics.
The Event Horizon Telescope, is a planet-scale array of eight ground-based radio telescopes that was designed to capture images of black holes. In April 2019, the EHT collaboration announced that it had successfully taken the first picture of the black hole at the center of the Messier 87 galaxy, with the results published in a series of six papers in the Astrophysical Journal Letters. The image, a bright ring formed by light bending around the black hole, quickly circled the globe, appearing across the front pages of newspapers and throughout social media. The 2020 Rossi Prize recognizes this historic scientific achievement.
The prize is in honor of Professor Bruno Rossi, an authority on cosmic ray physics and a pioneer in the field of X-ray astronomy. The Rossi Prize includes an engraved certificate and a 1,500 dollar award. Dr. Doeleman will give a lecture at the 237th AAS meeting in Phoenix, Arizona, in January 2021.
The European Research Council (ERC) has awarded a €2 million consolidator grant to GRAPPA researcher Christoph Weniger for the project “UnDark – New Approaches to Uncover Dark Matter in the post-WIMP Era”.
The goal of the ERC project UnDark is to discover particle dark matter in the post-WIMP era. Weniger will search for deviations from the cold dark matter paradigm by studying the dark matter distribution in the Universe at the smallest scales, and search for anomalous emission from dark matter particles across the electromagnetic spectrum. He will develop a ‘principled lampposts’ approach to systematically identify gaps in searches for a large number of dark matter models, and probe astrophysical hints for sterile neutrino and axion dark matter, which are some of the most promising dark matter candidates next to the WIMP. To this end, Weniger will leverage recent breakthroughs in computer science that enabled the deep learning revolution.
The ‘DarkGenerators’ proposal by GRAPPA researcher Christoph Weniger was awarded an Innovative eScience Technologies for ‘Big Science’ grant from the Netherlands eScience Center and SURFsara. With the grant, Weniger will use advanced data science methods to enhance and accelerate the interpretation of astrophysical and collider data in the search for signals of dark matter.
Weniger’s grant-winning proposal was titled ‘DarkGenerators – Interpretable Large Scale Deep Generative Models for Dark Matter Searches’. Dark matter is five times more abundant in the universe than visible matter. Yet, its nature remains unknown and constitutes one of the most exciting and complex research questions today. The project will use advanced data science methods to enhance and accelerate the interpretation of astrophysical and collider data in the search for signals of dark matter. Deep generative models and differentiable probabilistic programming will be used to construct a framework for the fast and precise inference of high-dimensional data models.
Exciting new results from observations of a star orbiting a massive black hole, published in a recent Nature paper.
Observation of the radial velocity variations of a Galactic star suggest it is orbiting a black hole, in a first taste of how the Galactic black-hole population could be revealed by future time-domain spectroscopic surveys. The visible star is inferred to be a B-type star with a mass roughly 8 times greater than that of the Sun; this star is in a circular orbit with a period of 78.9 days around an unseen mass. Together this indicates a system containing a black hole of at least 6 solar masses, and one which is wider than any previously known Galactic black-hole binary.
The most exciting possibility comes If a H-alpha emission line from the system is interpreted as indicating the motion of the black hole. In that case then the black hole is inferred to have a mass of 68 solar masses. This is highly unexpected. Even though gravitational wave experiments have detected similarly massive black holes, forming black holes as massive as that in high-metallicity environment would be extremely challenging to current evolution theories.
We are delighted to welcome Philipp Moesta as a faculty member at GRAPPA, shared between IHEF and API. Philipp’s research focuses on high-energy general-relativistic astrophysics.
Philipp expressed his excitement by stating, “I am very excited to be joining GRAPPA and building up a multimessenger astrophysics group here. It is transformative time to be working in general-relativistic astrophysics with the routine detection of gravitational waves, electromagnetic signals, and neutrinos from the most powerful explosions in the universe. I am particularly looking forward to exploring the connections between my expertise in simulating these explosions with the already existing gravitation and astroparticle groups at GRAPPA and am thrilled to be working together with the outstanding students, postdocs and staff members in Physics and Astronomy at UvA and Nikhef across the road.”
Philipp has started working with GRAPPA in July 2019. We look forward to his contributions to our intellectual community for many years to come.
Today two Nature papers appeared on the detection of a gamma-ray bursts in the 100 GeV domain, observed by MAGIC and HESS.
After a decade-long search, scientist have for the first time detected a gamma-ray burst in very-high energy gamma light, discovered by the H.E.S.S. collaboration in July 2018. This gamma-ray burst, an extremely energetic flash following a cosmological cataclysm, was found to emit very-high-energy gamma-rays long after the initial explosion. Extremely energetic cosmic explosions generate gamma-ray bursts, typically lasting for only a few tens of seconds. They are the most luminous explosions in the universe, The burst is followed by a longer lasting afterglow mostly in the optical and X-ray spectral regions whose intensity decreases rapidly. The prompt high energy gamma-ray emission is mostly composed of photons several hundred-thousands to millions of times more energetic than visible light, that can only be observed by satellite-based instruments. Whilst these space-borne observatories have detected a few photons with even higher energies, the question if very-high-energy gamma radiation is emitted, has remained unanswered until now.
GRAPPA member, Jacco Vink, is one of the co-authors on the H.E.S.S. paper. He calls it a great success, which testifies to the power of these type of gamma-ray telescopes for finding distant explosions. A big surprise was, according to him, that the emission was picked up so long after the initial explosion occurred.
The National Science Agenda has awarded a 5 million euro grant to CORTEX – the Center for Optimal, Real-Time Machine Studies of the Explosive Universe. The CORTEX consortium of 12 partners from academia, industry and society will make self-learning machines faster, to figure out how massive cosmic explosions work, and to innovative systems that benefit our society.
Machine learning has rapidly become an integral part of our lives. It is now commonly used for speech recognition and information retrieval. This is also true in science, for detecting patterns in nature and the Universe. But the need is growing rapidly for such machines to respond quickly, for example in self-driving cars and for responsive manufacturing. On a more fundamental level, self-learning machines help us unveil a dynamical Universe we did not know existed up until recently. Bright explosions appear all over the radio and gravitational-wave sky. Many citizens and scientists are curious to understand where these come from.
The University of Amsterdam GRAPPA, Anton Pannekoek Institute for Astronomy and Institute of Physics led efforts focus on the numerical modelling, joint characterisation and interpretation of neutron star binary mergers using gravitational wave and radio observations. The effort comprises the participation of the groups led by Samaya Nissanke (UvA work package contact and lead), Antonia Rowlinson (co-project lead), Philipp Moesta, Oliver Porth, and Sera Markoff.
We will be welcoming Camila Correa at GRAPPA, who, together with 166 young researchers have been granted a Veni grant. The Dutch Research Council (NWO) has awarded a Veni grant worth up to 250,000 euros to 166 highly promising young scientists. The grant provides the laureates with the opportunity to further elaborate their own ideas during a period of three years.
Dr Camila Correa (Leiden University) will conduct her research within GRAPPA on: Do dark matter particles interact with each other? The nature of dark matter is a great unsolved mystery. The proposed research project will use state-of-the-art simulations to analyse signatures of forces between dark matter particles on galaxies colliding, filling a major gap in our understanding of dark matter.
This year, twelve bachelor students completed the workshop that was organized by Shin’ichiro Ando, Bradley Kavanagh and Oscar Macias. The topic of this year’s workshop was the potential discovery of dwarf galaxies and the role these may play in searches for dark matter. The students were responsible for the lion’s share of the research that went into the paper, which was published in the Journal of Cosmology and Astroparticle Physics last week.
More information can be found at the IOP news, and the paper can be found here.
The Breakthrough Prize Foundation announced the recipients of the prestigious 2020 Breakthrough Prizes and 2020 New Horizons Prizes in recognition of important achievements in the Life Sciences, Fundamental Physics, and Mathematics. The Event Horizon Telescope collaboration, including several UvA scientists, was awarded the Breakthrough Prize, while UvA astrophysicist Samaya Nissanke received the New Horizons in Physics Prize.
The annual Breakthrough Prize in Fundamental Physics, for a total amount of $3 million, goes to the 347 scientists that co-authored the six papers published by the Event Horizon Telescope collaboration in April 2019. The papers announced the first image of a supermassive black hole, taken by means of an Earth-sized alliance of telescopes. Among the laureates are UvA scientists Sera Markoff, Oliver Porth and Koushik Chatterjee. UvA postdoc Doosoo Yoon also contributed to the EHT results.
The $100,000 New Horizons Prize recognizes early-career achievements in physics and mathematics. Samaya Nissanke, an assistant professor at the GRAPPA center of excellence at the University of Amsterdam, received the prize together with her colleagues Jo Dunkley (Princeton University) and Kendrick Smith (Perimeter Institute). The prize was awarded for their development of novel techniques to extract fundamental physics from astronomical data. In 2016, Nissanke was also a member of the team receiving a Breakthrough Prize for the detection of gravitational waves.
The new laureates will be recognized at the eighth annual Breakthrough Prize gala awards ceremony on Sunday, November 3, at NASA Ames Research Center in Mountain View, California, and broadcast live on National Geographic. Each year, the program has a theme, and this year’s topic – “Seeing the Invisible” – is inspired by the Event Horizon Telescope collaboration.
Samaya Nissanke has been elected as the new spokesperson for the Gravitation and AstroParticle Physics Amsterdam (GRAPPA) centre of excellence at the University of Amsterdam. Nissanke is the successor of Gianfranco Bertone, who was recently appointed director of EuCAPT.
Nissanke is currently an assistant professor at the University of Amsterdam. She is a joint faculty member at the Anton Pannekoek Institute for Astronomy and the Institute for High Energy Physics, and is already a member of GRAPPA.
Nissanke’s predecessor, Gianfranco Bertone, said: ‘I am sure that thanks to her scientific excellence, enthusiasm and leadership, Samaya will shine in this role. I look forward to seeing GRAPPA further strengthening its scientific impact and establishing its presence at the local, national and international level under her leadership.’
On July 10, 2019, a group of leading theoretical physicists active in fields of astroparticle physics and cosmology met with representatives of APPEC and CERN to kick-off EuCAPT (European Consortium for AstroParticle Theory), a new initiative that aims to coordinate and favour theoretical astroparticle and cosmology activities in European centres and institutions.
The steering committee of EuCAPT includes internationally renowned scientists affiliated to leading European institutions: Gianfranco Bertone (U. of Amsterdam), Philippe Brax (CEA Saclay), Vitor Cardoso (IST Lisbon), Gian Giudice (CERN), David Langlois (APC Paris), Silvia Pascoli (U. of Durham), Hiranya Peiris (UCL London & OKC Stockholm) Antonio Riotto (U. of Geneva), Subir Sarkar (U. of Oxford), Piero Ullio (SISSA Trieste), Andrew Taylor (DESY Hamburg), Licia Verde (U. of Barcelona). CERN has agreed to act as central hub for EuCAPT, and committed to provide financial and administrative support to its activities.
GRAPPA Spokesperson Gianfranco Bertone, who has been appointed EuCAPT director, said: “EuCAPT is a bottom-up initiative that aims to be open and inclusive. We will soon reach out to to the scientific community and to the broader society, with an invitation to participate in our exciting programme of scientific and outreach activities. Stay tuned!”.
The first EuCAPT activities will include one annual meeting of the entire theoretical astroparticle community that will take place at CERN starting in 2020, and two topical workshops at other participating institutions. More information on EuCAPT activities will be released in September, when the website of the initiative will be be launched.
We will welcome Kenny Ng to GRAPPA later this year, who has been awarded, together with ten talented researchers, a Marie Skłodowska-Curie Individual Fellowship to conduct research at the University of Amsterdam (UvA). The awarded projects include research on public support for different interpretations of ‘Social Europe’, the transmission of pathogens from animals to humans and metaphorical narratives in discourses on dementia. The awarded fellowships range from 175,000 to 280,000 euros. The grants are awarded as part of the Marie Skłodowska-Curie Actions, which forms part of the European Union’s Horizon 2020 research and innovation programme. The aim of the fellowship is to equip researchers with the necessary skills and international experience to pursue a successful career.
Kenny Ng’s research will be on understanding the peculiar gamma-ray emission of the sun.
With space telescopes, we only recently gained the sensitivity to precisely study the gamma rays from the Sun, presumably caused by energetic cosmic particles (cosmic rays) bombarding the Sun. Surprisingly, many properties of these gamma rays are not yet explained. Kenny Chun Yu Ng plans to understand them through new observational and theoretical investigations, which will ultimately help us better understand the Sun itself and the solar system space environment.
Kenny Ng will collaborate with Dr Shin’ichiro Ando here at GRAPPA.
If upcoming direct searches discover the elusive dark matter in the universe, they may be able to measure the mass of the particle or the way it interacts with ordinary matter, but can only do both if we’re lucky, researchers from the UvA Institute of Physics argue.
It is one of the great open questions of modern-day physics and astronomy: what is the mysterious dark matter in the universe? Astronomers suspect that the universe contains much more matter than they can see through there telescopes – simply because there is much more gravity than visible matter can account for. So far, however, nobody has been able to find particles that this dark matter can be made of.
Yet, many astronomers and particle physicists are optimistic that a dark matter candidate particle can be found soon, in the next generation of experiments and observations. While this may be true, Amsterdam researchers now point out that even if such a new dark matter particle is found, this does not automatically mean that we will immediately know all of its properties.
In their investigation, the researchers looked at planned underground detectors which aim to detect dark matter by looking for its rare interactions with ordinary atomic nuclei. The as yet undiscovered dark matter particle has an unknown mass (how heavy it is) and an unknown cross section (how strongly it interacts with nuclei).
Using new statistical tools, inspired by a concept known as ‘information geometry’ that the same researchers developed earlier this year, the physicists mapped out what a discovery would look like, without assuming a particular dark matter particle mass or cross section – allowing to explore a wide range of these dark matter properties.
New materials and techniques
It was found that a discovery using multiple different target materials that the dark matter particle can interact with, will substantially improve the measurement of the dark matter properties. However, even with multiple detectors, it will be hard to measure the mass of heavy dark matter particles and at the same time understand their precise interactions. Only over a narrow range of properties can both of these things be measured simultaneously.
This result, which was accepted for publication in Physical Review Letters last week, should spur the dark matter community to explore new detector materials and techniques which will improve the prospects for pinning down the properties of the dark matter particle in the event of a future discovery.
In a Nature review article published this week, physicists Gianfranco Bertone (GRAPPA, UvA) and Tim Tait (UvA and UC Irvine) discuss the past accomplishments and the current status of dark matter search experiments and how they will shape the future efforts for dark matter searches.
More information can be found at the IOP news.
The nature article can be found here and the pre-print version can be found here.
For almost ten years, astronomers have been studying a mysterious diffuse radiation coming from the center of our Galaxy. Originally, it was thought that this radiation could originate from the elusive dark matter particles that many researchers are hoping to find. However, physicists from the University of Amsterdam and the Laboratoire d’Annecy-le-Vieux de Physique Théorique have now found further evidence that rapidly spinning neutron stars are a much more likely source for this radiation.
Observations of the gamma-ray radiation from the Galactic center region with the Fermi Large Area Telescope have revealed a mysterious diffuse and extended emission. Discovered almost 10 years ago, this emission generated a lot of excitement in the particle physics community, since it had all the characteristics of a long-sought-after signal from the self-annihilation of dark matter particles in the inner Galaxy. Finding such a signal would confirm that dark matter, a substance that so far has only been observed through its gravitational effects on other objects, is made out of new fundamental particles. Moreover, it would help to determine the mass and other properties of these elusive dark matter particles. However, recent studies show that arguably the best astrophysical interpretation of the excess emission is a new population in the Galactic bulge of thousands of rapidly spinning neutron stars called millisecond pulsars, which have escaped observations at other frequencies up to now.
Figure 1. Observed gamma-ray emission from the Galactic disk, with the bulge region indicated. The insets show the expected profiles of excess radiation coming from dark matter and stars respectively. The researchers were able to show that the stars profile matches the measurements much better than the dark matter profile.
Where there are stars, there is radiation
‘Understanding in detail the morphology [the location and shape] and spectrum [the combined frequencies] of the excess emission is of vital importance for discriminating between the dark matter and astrophysical interpretations of the Galactic Center excess radiation.’, says Christoph Weniger, one of the researchers that conducted the study. A new study by researchers at the University of Amsterdam and the Laboratoire d’Annecy-le-Vieux de Physique Théorique, a research unit of the French Centre National de la Recherche Scientifique, found strong evidence that the emission actually seems to come from regions where there is also a large amount of stellar mass in the Galactic bulge (the ‘boxy bulge’) and center (the ‘nuclear bulge’). Furthermore, the researchers found that the light-to-mass ratio in the Galactic bulge and center are mutually consistent, so that the gamma-ray GeV emission is a surprisingly accurate tracer of stellar mass in the inner Galaxy – see figure 2. This study was based on a new analysis tool, SkyFACT (Sky Factorization with Adaptive Constrained Templates), developed by the researchers themselves, which combines physical modeling with image analysis.
Figure 2. Comparison of the stellar mass (horizontal axis) and gamma-ray luminosity (vertical axis) for the “boxy bulge” (in blue) and for the “nuclear bulge” (in green). The prediction for a population of millisecond pulsars in the Galactic disk (in red) and the bulge of the nearby Andromeda galaxy (M31, in pink) are also shown. Stellar mass and luminosity are proportional to each other in the inner Galaxy (dashed line), which shows that the mysterious excess radiation very likely has a stellar origin and is not coming from dark matter.
The findings support the millisecond pulsar interpretation of the excess emission, since neither a dark matter signal nor other astrophysical interpretations are expected to show such a correlation. ‘The results will help guide upcoming radio searches for this hidden population of millisecond pulsars in the Galactic bulge with MeerKAT and the future Square Kilometre Array’, said Francesca Calore, another of the paper’s authors. ‘This makes these upcoming searches even more promising.’
R. Bartels, E. Storm, C. Weniger and F. Calore, The Fermi-LAT GeV excess traces stellar mass in the Galactic bulge, Nature Astronomy 2018.
In January 2018, UvA-IoP/GRAPPA researchers Shin’ichiro Ando and Bradley Kavanagh led a team of 9 bachelors students to investigate radiative neutrino decay and its impact on the cosmic microwave background. They set precise constraints on the neutrino lifetime, which was found to be orders of magnitude longer than the age of the universe. More information can be found at the IOP news .
This year’s TeVPA will be hosted in Berlin, Germany from 27 – 31 August, 2018. TeVPA is a five day conference which aims to bring together leading scientists in the field to discuss recent advances in Astroparticle Physics. Early bird registration closes on July 7, 2018.
We are delighted to welcome Samaya Nissanke as a faculty member at GRAPPA, shared between IHEF and API. Samaya’s current research focuses on the detection, measurement and interpretation of gravitational waves, the astrophysics of compact object (black holes, neutron stars and white dwarfs) binaries, and general relativity.
Samaya expressed her excitement by stating, “I am very excited to be joining the GRAPPA department and building a new dynamic gravitational wave and multi-messenger astrophysics group here. It is an incredible time to be working in strong-field gravity astrophysics thanks to the recent gravitational wave detections, time-domain electromagnetic surveys and astroparticle experiments, and recent advances in cosmology and computational astrophysics. I am greatly looking forward to the many scientific adventures here, and working with the excellent students, postdocs and staff members in both the physics and astronomy departments at UvA, as well as the nearby Nikhef institute.”
Samaya will start her first day at GRAPPA on June 15. We look forward to her contributions to our intellectual community for many years to come.
GRAPPA, the center of excellence in Astroparticle Physics of the University of Amsterdam, is a joint effort between the Institute for High Energy Physics, the Anton Pannekoek Institute, and the Institute for Theoretical Physics. It consists of eight faculty members – S. Ando, D. Baumann, G. Bertone (spokesperson), M.P. Decowski, B. Freivogel, S. Markoff, J. Vink and C. Weniger – whose research interests include black holes, cosmic rays, neutrinos, dark matter, dark energy, early universe cosmology, and string theory. In addition, there are about 15 affiliated GRAPPA faculty who are involved with experimental work on Antares/KM3NeT, ATLAS, CTA, LIGO/VIRGO, LOFAR and XENON100/XENON1T, as well as theory.
We invite applications for one or more postdoctoral positions in the fields of particle and astroparticle physics. One of the successful candidates will work in an interdisciplinary team led by G. Bertone. We are looking in particular for candidates who have experience in applying machine learning methods to particle and astroparticle physics problems. Candidates who have shown excellence in other relevant fields and are willing to broaden their research interests are also encouraged to apply. Additional postdoctoral positions might become available in the group of Christoph Weniger. All candidates will be automatically considered for those positions.
The appointment is for two years (with a possible extension to a third year), with a salary set by Dutch labor law, including generous benefits. Candidates should preferably have obtained a PhD in a field related to the group’s research interests after December 2013, or expect to obtain it by September 2018.
Artis Planetarium and GRAPPA are proud to present an evening on The Dark Universe.
Gianfranco Bertone (IoP/ GRAPPA), Hiranya Peiris (UCL) and Jocelyn Monroe (Royal Holloway, University of London) will give talks and answer questions on different aspects of the Dark Universe, moderated by popular science writer Govert Schilling.
The discussion will be followed by a screening of the film The Dark Universe, which was made by researchers at the American Museum of Natural History in New York for their exhibition on the same subject.
This event forms part of the social programme for GRAPPA@5, a conference organised in celebration of GRAPPA’s 5th anniversary. The evening will be aimed at a general audience and will be given in English.
The evening will take place at Artis Planetarium:
Plantage Kerklaan 38-40
1018 CZ Amsterdam
A tenure track position in the field of gravitational waves astrophysics is available in our group.
We are looking for a candidate with an exceptionally strong research program and a strong interest in excellent teaching in the areas of interest of GRAPPA, with a strong preference for candidates working in gravitational-wave astrophysics. For a balanced composition of GRAPPA, we also have a strong preference for female candidates.
The candidate is required to have a PhD in (astro-)physics, an excellent scientific track record, and the proven capability to attract funding. The candidate should have the capabilities to build up a research group of internationally outstanding level and to initiate and carry out scientific research. The candidate should also be able to develop and provide allotted cohesive academic course components for a wide range of target groups, based on the faculty’s curriculum, so that students may meet the course objectives in terms of knowledge, understanding, skills, competence and attitude.
The initial appointment will be for a period of six years. Based on performance indicators agreed on at the start of the appointment, the tenure track position will lead to a tenured position in a period of maximally 5 years. In the fifth year of the appointment the tenure decision will be taken. These conditions can be tailored appropriately for candidates that have somewhat greater seniority. Exceptional candidates may be directly considered for a tenured position.
We cordially invite you to “GRAPPA @ 5”, a symposium on astroparticle physics to be held in Amsterdam from 16 – 18 October 2017.
In 2012 the University of Amsterdam started Gravitation Astroparticle Physics Amsterdam (GRAPPA), its new excellence center for astroparticle physics. After five years GRAPPA has become an household name in astroparticle physics, and a thriving place to do astroparticle physics research, involving around 50 researchers.
In order to celebrate the 5 years of GRAPPA we are organising a symposium devoted to astroparticle physics. We have an impressive list of invited speakers who will inform you about the current state of astroparticle physics: John Beacom, Lars Bergström, Esra Bulbul, Luke Drury, Stefan Funk, Francis Halzen, Stavros Katsanevas, Matthew Kleban, Nergis Mavalvala, Jocelyn Monroe, Hiranya Peiris and Tim Tait. Apart from a host of excellent invited speakers we also have a number of open slots for interesting contributions in the field of astroparticle physics.
In addition to the symposium we will have a welcome reception on October 16, and a dinner/party on October 17 at two very interesting locations!! Thanks to contributions from several sponsors the contribution fee will be only 55 euro.
Please register here: https://indico.cern.ch/event/608844/. The poster for the symposium is also available for download on the conference website.
An interdisciplinary team of physicists and astronomers at the University of Amsterdam’s GRAPPA Center of Excellence for Gravitation and Astroparticle Physics has devised a new strategy to search for ‘primordial’ black holes produced in the early universe. Such black holes are possibly responsible for the gravitational wave events observed by the Laser Interferometer Gravitational-Wave Observatory. In a paper that appeared in Physical Review Letters this week, the researchers specifically show that the lack of bright X-ray and radio sources at the center of our galaxy strongly disfavours the possibility that these objects constitute all of the mysterious dark matter in the universe.
Primordial black holes
The existence of black holes tens of times more massive than our Sun was confirmed recently by the observation of gravitational waves, produced by the merger of pairs of massive black holes, with the LIGO interferometer. The origin of these objects is unclear, but one exciting possibility is that they originated in the very early universe, shortly after the Big Bang. It has been suggested that these ‘primordial’ black holes may constitute all of the universe’s dark matter – the mysterious substance that appears to permeate all astrophysical and cosmological structures, and that is fundamentally different from the matter made of atoms that we are familiar with.
An interdisciplinary team of UvA physicists and astronomers proposed to search for primordial black holes in our galaxy by studying the X-ray and radio emission that these objects would produce as they wander through the galaxy and accrete gas from the interstellar medium. The researchers have shown that the possibility that these objects constitute all of the dark matter in the galaxy is strongly disfavoured by the lack of bright sources observed at the galactic center.
‘Our results are based on a realistic modelling of the accretion of gas onto the black holes, and of the radiation they emit, which is compatible with current astronomical observations. These results are robust against astrophysical uncertainties’, says Riley Connors, PhD student at the UvA and an expert in black hole astrophysics. ‘What’s even more interesting”, adds Daniele Gaggero, first author of the publication, ‘is that with more sensitive future radio and X-ray telescopes, our proposed search strategy may allow us to discover a population of primordial black holes in our galaxy, even if their contribution to the dark matter is small.’
‘A convincing implementation of our original idea was possible thanks to the collective effort of an interdisciplinary team of scientists at the GRAPPA Center of Excellence for Astroparticle Physics’, says Gianfranco Bertone, GRAPPA spokesperson. ‘This includes theorists studying dark matter and the formation of black holes, astrophysicists modelling the subsequent accretion process, and astronomers working on radio and X-ray observations.’
The new findings are expected to shed light on the formation and origin of primordial black holes as well as of standard astrophysical black holes that are formed when stars collapse.
Searching for Primordial Black Holes in the radio and X-ray sky, Daniele Gaggero, Gianfranco Bertone, Francesca Calore, Riley M.T. Connors, Mark Lovell, Sera Markoff and Emma Storm, Phys. Rev. Lett. 118, 241101 [arXiv: 1612.00457].
Physicist Shin’ichiro Ando was awarded the prestigious Japanese Grant-in-Aid for Young Scientists. Ando, a member of the center of excellence for Gravitation and Astroparticle Physics Amsterdam, will use the grant for his research in astroparticle physics, high-energy astrophysics, and cosmology.
Next to his full-time position at UvA, Ando has also been affiliated to the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) at the University of Tokyo since the fall of 2016. The Grant-in-Aid for Young Scientists is the biggest Japanese grant for young individual researchers, similar to the Vidi grant in the Netherlands. The grant, awarded through Kavli IPMU, consists of an amount equivalent to €200,000, and can be spent over the next four years on travel, equipment and postdoc salaries. Ando will also take this as an opportunity to facilitate exchange of knowledge and people between Amsterdam and Tokyo.
The nature of dark matter is one of the most important open problems in today’s physics. When, how and why did scientists accept that most matter in the universe is actually invisible and unknown to us? An interdisciplinary collaboration of historians and physicists at the Institute of Physics, the GRAPPA Center of Excellence, and the Vossius Center has revisited these questions. Their results inform us about past and current practices in cosmology.
PhD student Jaco de Swart, astroparticle physicist Gianfranco Bertone and historian of science Jeroen van Dongen study the history of ‘how dark matter came to matter’. Their first results are published in an article in Nature Astronomy this week.
Forty years of darkness
Dark Matter has a long history. In the 1930s, first observations suggested that galaxies in clusters are moving so rapidly that their velocities cannot be understood by familiar and visible matter. Still, it took 40 years before consensus on this conclusion was reached. ‘[A] lot of things were not understood about masses of astronomical objects on the scales of galaxies and larger’, eminent physicist Jim Peebles recalled in an interview with Jaco de Swart. Peebles played a central role in the 1970s in convincing the scientific community that most of the matter in the universe is unknown to us: it is literally ‘dark’. But why did it take so long for scientists to realize this?
De Swart, Bertone and Van Dongen studied original sources, interviewed pioneering scientists and reconstructed the historical context of the dark matter hypothesis. In their paper, they show that newly observed phenomena, as well as institutional developments, partly driven by the Cold War, led astronomers and physicists to focus on cosmological problems. A quest to determine the mass density of the universe began: it is this mass density which decides the ultimate fate of the universe. In the search for the universe’s mass, galactic dynamics was finally taken to imply that 85% of the universe’s matter is missing.
History for the future
Collaborations between physicists, historians and philosophers are necessary to deepen our understanding of cosmology and dark matter. What kind of arguments and inferences are used in cosmology? When does data turn into evidence for astrophysicists? Answers to these questions will inform today’s heated debates on the nature of dark matter and the proper practice of cosmology.
Researchers from the University of Amsterdam’s (UvA) GRAPPA Center of Excellence have just published the most precise analysis of the fluctuations in the gamma-ray background to date. By making use of more than six years of data gathered by the Fermi Large Area Telescope, the researchers found two different source classes contributing to the gamma-ray background. No traces of a contribution of dark matter particles were found in the analysis. The collaborative study was performed by an international group of researchers and is published in the latest edition of the journal Physical Review D.
Gamma rays are particles of light, or photons, with the highest energy in the universe and are invisible to the human eye. The most common emitters of gamma rays are blazars: supermassive black holes at the centers of galaxies. In smaller numbers, gammy rays are also produced by a certain kind of stars called pulsars and in huge stellar explosions such as supernovae.
In 2008 NASA launched the Fermi satellite to map the gamma-ray universe with extreme accuracy. The Large Area Telescope, mounted on the Fermi satellite, has been taking data ever since. It continuously scans the entire sky every three hours. The majority of the detected gamma rays is produced in our own Galaxy (the Milky Way), but the Fermi telescope also managed to detect more than 3000 extragalactic sources (according to the latest count performed in January 2016). However, these individual sources are not enough to explain the total amount of gamma-ray photons coming from outside our Galaxy. In fact, about 75% of them are unaccounted for.
Isotropic gamma-ray background
As far back as the late 1960s, orbiting observatories found a diffuse background of gamma rays streaming from all directions in the universe. If you had gamma-ray vision, and looked at the sky, there would be no place that would be dark.
The source of this so-called isotropic gamma-ray background has hitherto remained unknown. This radiation could be produced by unresolved blazars, or other sources too faint to be detected with the Fermi telescope. Parts of the gamma-ray background might also hold the fingerprint of the illustrious dark matter particle, a so-far undetected particle held responsible for the missing 80% of the matter in our universe. If two dark matter particles collide, they can annihilate and produce a signature of gamma-ray photons.
Together with colleagues, Dr Mattia Fornasa, an astroparticle physicist at the UvA and lead author of the paper, performed an extensive analysis of the gamma-ray background by using 81 months of data gathered by the Fermi Large Area Telescope – much more data and with a larger energy range than in previous studies. By studying the fluctuations in the intensity of the gamma-ray background, the researchers were able to distinguish two different contributions to the gamma-ray background. One class of gamma-ray sources is needed to explain the fluctuations at low energies (below 1 GeV) and another type to generate the fluctuations at higher energy – the signatures of these two contributions is markedly different.
In their paper the researchers suggest that the gamma rays in the high-energy ranges – from a few GeV up – are likely originating from unresolved blazars. Further investigation into these potential sources is currently being carried out by Fornasa, fellow UvA researcher Shin’ichiro Ando and colleagues from the University of Torino, Italy. However, it seems much harder to pinpoint a source for the fluctuations with energies below 1 GeV. None of the known gamma-ray emitters have a behaviour that is consistent with the new data.
Constraints on dark matter
To date, the Fermi telescope has not detected any conclusive indication of gamma-ray emission originating from dark-matter particles. Also, this latest study showed no indication of a signal associated with dark matter. Using their data, Fornasa and colleagues were even able to rule out some models of dark matter that would have produced a detectable signal.
‘Our measurement complements other search campaigns that used gamma rays to look for dark matter and it confirms that there is little room left for dark matter induced gamma-ray emission in the isotropic gamma-ray background’, says Fornasa.
The data that were analysed in the work described here. Fluctuations in the isotropic gamma-ray background, based on 81 months of data. Emission from our own Galaxy, the Milky Way, is masked in grey. (Credits: Mattia Fornasa, UvA/Grappa)
Mattia Fornasa, Alessandro Cuoco, Jesús Zavala, Jennifer M. Gaskins, Miguel A. Sánchez-Conde, German Gomez-Vargas, Eiichiro Komatsu, Tim Linden, Francisco Prada, Fabio Zandanel and Aldo Morselli: ‘The Angular Power Spectrum of the Diffuse Gamma-ray Emission as Measured by the Fermi Large Area Telescope and Constraints on its Dark Matter Interpretation’ in Physical Review D. D 94, 123005, 9 December 2016.
GRAPPA (GRavitation and AstroParticle Physics in Amsterdam) is a center of excellence of the University of Amsterdam. GRAPPA brings together theoretical physicists, astronomers and particle physicists in order to answer some of the most profound questions in particle astrophysics and cosmology: What is the so-called dark matter? How was the universe created? Where do cosmic rays originate? What bounds the smallest particles? The GRAPPA members who contributed to this research paper are Mattia Fornasa (lead author), Jennifer M. Gaskins and Fabio Zandanel.
The European Research Council has awarded a prestigious Consolidator Grant to GRAPPA researcher Ben Freivogel, for the project “Quantifying Quantum Gravity Violations of Causality and the Equivalence Principle”
Freivogel’s ERC project intends to accurately identify the circumstances and scales where quantum-mechanical effects of gravity become relevant. Although these quantum effects are typically believed to be extremely tiny on scales that can be probed experimentally, recent results of Freivogel and others suggest that under certain circumstances quantum gravity effects can become large and perhaps even observable on much larger, macroscopic, length scales. This could in particular have major consequences for the possibility to probe quantum gravity through cosmology.
We invite applications for a joint postdoctoral position at the GRAPPA center of excellence in Astroparticle Physics at the U. of Amsterdam, and at the Lorentz Institute at the U. of Leiden. Preference will be given to candidates with expertise in the application of advanced statistical methods and/or machine learning, to astronomy and/or particle physics. The appointment is for two years with a starting date in the Fall 2017.