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StrongGravity Report Summary

Project ID: 312789
Funded under: FP7-SPACE
Country: Czech Republic

Periodic Report Summary 2 - STRONGGRAVITY (Probing Strong Gravity by Black Holes Across the Range of Masses)

Project Context and Objectives:
The objective of STRONGGRAVITY is to develop analytical tools to study processes occurring near astrophysical black holes, acquire observational data on the Galactic solar-mass black holes in binary systems, super-massive black holes in the centres of galaxies and our central black hole of the Milky Way, and use the created tools together with the new and archival data for better understanding the properties of black holes and their immediate neighbourhood.
Black holes provide a crucial link between Einstein’s theory of gravity and real cosmic objects which astronomers can observe and study in the Universe. This project is oriented towards legacy of the cornerstone XMM-Newton X-ray satellite mission of European Space Agency in synergy with relevant data in other spectral domains that are covered by ground-based infrared and radio interferometric techniques at European Southern Observatory and elsewhere. Information in different wavelengths will be gathered and explored in order to understand radiation processes in places of strong gravity, near black holes.
It is almost impossible to see black holes directly, therefore it is the observation of the matter moving in close vicinity of these objects, either orbiting them, falling down upon them or being ejected from their neighbourhood that can reveal their properties. In this project we will analyse and interpret multiwavelength spectral and fast timing observations of systems containing different kinds of black holes, according to their mass – the solar-mass black holes in the binary systems in our Galaxy and the supermassive black holes in the centres of galaxies with masses of more than billion suns.
Over the course of the project, we are seeking valuable data from archives and complement them by performing new observations where needed. Our main objective is to use and enhance computational tools that the participating groups have been developing over two decades, and to join our effort in a dedicated program of data analysis and science interpretation of the most bizarre cosmic objects – black holes.

Project Results:
During the first two project periods, the StrongGravity project has already made a number of significant achievements and has produced many important results.
We have been developing new methods and analytical tools that are set off to be used with the observational data to model physical properties of active galaxies, Milky Way's central black hole or black holes in binary stars. Those tools are now largely finished and ready to be used to study spectral and timing characteristics of systems of interest. Our codes predict shapes of spectra of radiation that comes from a hot corona surrounding black holes as well as how this radiation is reprocessed by reflection from the surface of an accretion disk. We also compute variability patterns from which we can reconstruct physical properties of the corona from the observed reflected radiation. Other codes deal with modeling characteristics of ambient gas media in accretion disc winds and warm absorbers with the aim to uncover their column densities, inclinations, distances and speeds. The sparse flares that are produced by the super-massive black hole in the center of our galaxy are modeled with our polarimetric code with the aim of constraining spin and inclination of the central black hole and learn about the mechanisms and the geometry of the emitting region.
Our second main focus has been on data exploitation. We have acquired observational data from numerous instruments both ground-based and space-born and this newly obtained data has been completed with archive data when needed. We have been largely successful in securing observing time at some of the most powerful X-ray and infrared instruments like XMM-Newton, NuStar or VLT telescope and Large Binocular Telescope to gather the top-class data of sources of our interest. Those data together with the archive data have been then analyzed using the tools that we have been developing and we have already published some important findings.
In accordance with our commitment to “use the analytical tools provided by our project in the preparation of the ESA mission projects and to provide accurate simulations for the scientific performance of next generation space-based X-ray observatories,” we have contributed to the successfully accepted proposal of the new X-ray mission Athena, which will be the next big thing in X-ray astronomy once launched (almost half of the researchers from our consortium are involved), and to other smaller proposals for X-ray/polarimetry missions (Loft, Xipe, Ixpe, Xilpe, PolStar). We also contribute to development of infrared spectrometer instruments for both James Webb Space Telescope and for the European Extremely Large Telescope.
The consortium has so far published 126 papers in scientific journals and presented its results on 134 occasions at scientific conferences and workshops. Beside of that there has been a strong encouragement in public outreach – the project has been presented in several national TV news and shows, on radio and in popular magazines. Several public lectures have been given to spread the knowledge and excitement to the civil society. A special section on the project web page is devoted to public outreach and explains the fundamentals of black-hole physics and accretion and another section is dedicated to astrophysical community to spread the codes developed by our consortium.

Potential Impact:
The StrongGravity project brings together theoreticians and observers from seven different European countries with the goal of producing a significant leap forward in the understanding of strong gravity effects around black holes. In particular, we aim at obtaining the most reliable census so far of the spin of the black holes in both stellar-mass and super-massive black holes. This objective will be reached by a combination of theoretical/computational and observational efforts. We are pursuing the following two lines of research:
I. Develop new tools for the computation of the spectral, timing and polarization properties of the radiation emitted close to the black hole. These tools will include all relevant physical processes at work in these systems, to account for the effects of general relativity on the properties of the radiation, and the further modifications due to the interaction of photons with matter in the surroundings of black holes. We will then be able to determine the best signatures of GR effects, separating them from other effects. The tools will be made compatible with public data analysis packages, so that they can be used freely by the community at large.
II. Apply the tools to data (either from the public archives or obtained via dedicated proposals) mainly from current and near-future X-ray satellites. In particular, the data from European Space Agency (ESA) satellite XMM-Newton (whose scientific products and archives are maintained at ESAC) will be heavily exploited. We will then be able to measure, more precisely and robustly than now, the spin of the black holes and, in more general, to improve upon our knowledge of the strong gravity effects around black holes across the range of masses. In addition to that, we will be able to provide accurate simulations for the scientific performance of next generation space-based X-ray observatories as they are currently considered by ESA.
The project will contribute to fundamental science in astrophysics, and the main exploitation/dissemination of the results will consist, as customary for this kind of research, in scientific papers published in international refereed astrophysical journals and in presentations at international conferences. Our results are thus going to be spread in the scientific community by the usual channels; they will trigger new discussions in our field, and thereby give additional drive to the scientific progress.
It is important to us that our modelling and observational analysis can be tested and possibly extended by other research groups. Therefore we will set up a web site in which the computational tools will be described and made available for download. The results of our research will also be promoted on line as well as our related scientific papers and presentations. We are certain that our tools are going to be used outside of our collaboration as well and we presume that they give rise to new developments or even scientific ideas in Europe and elsewhere.

List of Websites:

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Czech Republic
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