Sera Markoff, Monika Moscibrodzka, Wanga Mulaudzi, Aristomenis Yfantis

In 2020 and beyond, Event Horizon Telescope (EHT) will continue to expand in bandwidth, number of stations and observation runs. The objective of this WP is to build a robust, end-to-end pipeline to perform data and calibration/error analysis on large volumes of data, capable of handling the new problems inherent to multi-frequency runs and variability. This is necessary to understand the next EHT black hole target Sgr A*, which varies on timescales as short as minutes compared to the much slower varying M87*, as well as to connect the event horizon scales to the enormous jet structures observed across the electromagnetic spectrum, at galactic scales.

Heino Falcke, Noemi La Bella

The first run of EHT analysis focused on relatively ‘simple’ theoretical scenarios of magnetized material falling onto a spinning black hole. With the increased precision of the expanded array and multi-frequency expansion described in WP1, the main objective of WP2 is to further develop theoretical simulations to be able to conduct a more extensive exploration of black hole parameters as well as detailed tests of GR, including alternatives to black holes.

Chris Van Den Broeck, Samaya Nissanke

Since 2015, binary mergers of (presumed) black holes and neutron stars are being observed on a regular basis by the LIGO and Virgo gravitational wave (GW) detectors, with a detection rate that is currently reaching about one per week [18,19]. With expected upgrades in detector sensitivities already over the next few years, we will soon be in a position to address a question that goes to the core of this proposal: how certain can we be that the massive binary objects whose mergers we have been observing are the standard (Kerr) black holes of classical general relativity?

Alejandra Castro, Frank Saueressig, Jildou Hollander

In this work package we want to deepen our theoretical knowledge of black holes and black hole
mimickers and to confront our theoretical understanding with experiment. This will help optimize the data analysis and simulations and guide the search for novel physical phenomena in WP1, WP2 and WP3, and provide valuable input for experimental design choices.

Geert-Jan Vis, Michiel van der Meulen, Jasper Maars

With this work package we want to study the possible location for the Einstein Telescope (ET) in South-Limburg. To do so, we will develop a 3D geological model of the desired location, based on updated geological concepts.  Also we want to make our data available for geothermal exploration. The model will be made freely available on TNO’s digital portal.

Stefan Hild, Alessandro Bertolini, Enrico Porcelli

Currently gravitational waves (GW) observatories LIGO and VIRGO are limited, in their most sensitive frequency band, by Brownian noise, thermally induced fluctuations of the mirror front surface position associated with the mechanical losses in the substrate and, mainly, in the high reflectivity multi-layer coating. In this respect, a major leap forward is expected in the Einstein Telescope (ET) by replacing the standard fused silica mirrors with larger ones made out of single crystal silicon and cooling them down either to 123K or 10K. A world wide effort is ongoing in the GW community to develop high reflectivity coatings optimized for low temperatures and for the longer laser wavelengths (1.55-2μm) dictated by the silicon substrates. It is crucial, in order to inform the ET design, to be able to perform direct precision measurements of coating thermal noise (CTN) at low temperature. The reason is that, besides the novelty of substrate and coating materials, the cryogenic environment poses new challenges as, for example, the adsorption of vacuum residual gas (mostly water molecules) on the surface of the cold mirror. The adsorbed layer causes changes in the mirror reflectance, transmittance and absorption, and it might affect the CTN figures as well due to the introduced additional mechanical losses [21]. We propose to realize the first worldwide lab-scale setup to perform CTN direct measurements on cold sample mirrors, by using the same interferometric technique successfully applied by Evans and Gras [22] at room temperature. Such an instrument, by providing rapid and accurate characterizations of the coating losses, will naturally complement and support the activities of larger R&D infrastructures like the ETPathfinder now in construction at University of Maastricht.

Pedro Russo, Joanna Holt,

With this workpackage we want to stimulate interest in science and technology amongst young people with a focus on girls and under-represented minorities.  We will also develop a lesson package for the last years of primary education called “Frontiers of Science: Black Holes”. Additionally we offer teacher training for both primary and secondary school teachers and research experience for secondary school teachers, with a focus on teachers from schools with students with low uptake in STEM studies. In the end we also want to engage with national educational policymakers and key national textbook publishers and advocate for use of black holes content and educational resources in formal educational textbooks.

Elwin Savelsbergh, Marijn van Nijhuis

In collaboration with the institutes in the consortium and the teacher education program of Utrecht University of Applied Sciences, a network will be set up to get researchers into teacher education programs, and to provide site visits and short-term intensive research internships for teacher education candidates. In a design research approach, a training module will be developed to precede and to conclude the research experience. Participants’ experiences will be documented through observations and reflective logs and participants’ understanding both about the black holes and about the process of doing research will be monitored before and after the program.

Peter Jonker, Elena Rossi, Steven Bloemen

We will use the three newly built telescopes located in Chile called BlackGEM for a citizens science project (see www.blackgem.org). These NOVA, Radboud University and KU Leuven-funded telescopes will automatically find thousands of "transients" each night. These transients are new "stars" appearing suddenly where no star or object was detectable before. These new objects can be caused by many phenomena, including a massive star exploding while its core implodes to a black hole (a so called supernova), the formation of a small black hole after two small compact stars called neutron stars merge, and a massive black hole ripping apart a star that wandered too close (a so called tidal disruption event). BlackGEM's data will be processed in the Google Cloud, and advanced machine learning techniques will help to weed out false positives such as new "stars" appearing due to asteroids, man-made satellites orbiting Earth, charged particles hitting the telescope detectors and other artefacts. A small number of such false positives is expected to remain even after the machine learning filters have been applied. However, people can filter these remaining false positives out effectively. Furthermore, citizens can provide context to the thousands of good transient events detected each night. By looking at what is located around the position of the transient citizens will inform astronomers who can then prioritise the objects based on this information. The reason behind this prioritisation is that the astronomical resources to obtain follow-up information are limited. We only want to follow up events involving black holes. A completely new aspect to this citizens science project is that citizens can do their classification work in near real- time. It takes only minutes for the data to be processed and for the transient candidates to appear in the Google Cloud ready for citizens to add their part. Research has shown that citizens appreciate that their work contributes to science done now. An aspect under study is whether citizens with a proven track record can trigger follow-up observations on one of the Las Cumbres Observatory (LCO) telescopes for which in-kind time has been made available to our Dutch Black Hole consortium.

Jeroen van Dongen, Emilie Skulberg, Annelore Scholten, Ad Maas

We want to prepare and organize a Black Hole exhibition at Rijksmuseum Boerhaave and do a  historical-philosophical study of black hole image in theory and observation. 

The concept of a black hole has pushed science to the boundaries of what is known and what can be known about the most fundamental building blocks of nature:space, time, matter, and the laws governing these. Thus, it provides a unique opportunity for Boerhaave to shed light on cutting edge science. The exhibit will take as a central theme what the image of the black hole is, what it has been, and how these images have been formed in different research traditions. All DBHC researchers will deliver input for this, either by research or educational material. Similarly, we wish to show at Boerhaave how today’s string theorists in their highly abstract approach ‘imagine’ a black hole (see also WP4). String theory notions of black hole entropy and holography suggest that space and time are ‘emergent’. How are they currently informing black hole observational efforts? These issues offer unique opportunities to present today’s most abstract science in a museum: no museum, as far as we are aware, has ever attempted to exhibit the concepts of string theory, despite its strong hold on the public’s imagination. This exhibit, thus, will clearly innovate science communication. Finally, novel audio-visual and other educational materials will be developed that showcase DBHC research. These will feature at the exhibits of WP9-10 and circulate with open access afterwards. 

With our historical-philosophical study of black hole image in theory and observation we want to answer the question: how do particular research traditions shape what is considered to be a black hole? String theorists’ insight into the microphysics of black holes is not without critics: observation is absent in such accounts. How universal is then the notion of scientific progress, and what role does empirical observation play in today’s theory construction? Furthermore, black holes cannot directly be seen (except perhaps for their still hypothetical Hawking radiation), yet are claimed to be observed all the time since the X-ray binary Cygnus-1 was identified as containing a black hole in 1972. There is a general sense that the observation of black holes has increasingly become more ‘direct’, as illustrated by the EHT’s black hole photo and LIGO’s gravitational wave detection. But what does ‘observing’ a black hole actually mean according to various groups of astronomers and physicists? What ‘images’ of a black hole are made in the various research traditions, and how have images of black holes changed in the interaction between theory and observation over time? This activity will strongly collaborate with WP1, 2, and 4. Emilie Skulberg will research how different images and understandings of black holes are tied to different traditions in modern fundamental physics, and thus offer insight on what is and what is not universal about observation and the empirical in modern day notions of scientific rationality and progress. 

Gideon Koekoek, Gène Bertrand, Mischa Horninge

The creation, in close collaboration with Stichting Museumplein Limburg (Continium discovery center, Columbus earth center and Cube design museum), of a large screen dome film of fundamental gravitational wave physics and its instrumentation, and of the local efforts in the province of Limburg in developing the region. This movie aims to inform and enthuse the general public, and to offer a natural and inspiring meeting point for politicians and other stakeholders to learn about the prospect of the ET-Pathfinder and the Einstein Telescope.