NOVA Network 3

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merging-black-holes

Simulated image of two black holes that are about to merge. Their strong gravitational fields warp the light of stars and galaxies in the background. In the process of merging, gravitational waves are emitted. The image above is representative of the merger event detected by the Laser Interferometer Gravitational wave Observatory (LIGO) in September 2015. Image courtesy of the Simulating eXtreme Spacetimes project.

Network 3: Astrophysics in extreme conditions

Network 3 focuses on the physics of compact objects and the interaction with their environment. Stellar compact objects, such as white dwarfs, neutron stars, and stellar-mass black holes are the end products of stellar evolution and are often found in binaries. Super-massive black holes in the centers of galaxies, have very different formation history, but share very similar physics and allow the study of black holes on different scales.  Compact objects manifest themselves as sources of high-energy radiation, non-thermal emission, highly energetic particles, gravitational waves, and high time variability. They are also natural sites to study the physics of strong gravity, dense matter, extremely high magnetic fields, accretion processes, and particle acceleration. Its main themes are: (1) Fast transients, (2) Accretion, ejection and feedback, (3) Physics of compact objects, (4) From binary star to high-energy phenomena and (5) Supernova remnants as particle accelerators.

NOVA instrumentation that is particularly important for Network 3 includes VLT X-Shooter, LOFAR, ARTS, BlackGEM and CTA, as well as the AMUSE software framework for multi-physics simulations. LOFAR operations are now routine and recent results range from AGN and radio galaxies, via transients and radio pulsars to the signals of cosmic rays interacting with the Earth atmosphere. The latter were even used to study the origin of lightning in our atmosphere.

Two topics that bring together different groups in the network are Tidal Disruption Events (TDEs), in which a star is disrupted around a black hole producing a sudden burst of accretion, and transitional millisecond pulsars, i.e., binary systems with a neutron star that switches between a state of accretion from the companion to being a radio pulsar and, unexpectedly, back. For both topics the focus is still on discovery and characterization of these objects, but they promise to give a new view on (rapid) accretion and properties of black holes for the TDEs and on the evolutionary link between accreting neutron stars and radio pulsars, as well as the interaction between the pulsar and the companion star.

There is also much research on type Ia supernovae. A unique population synthesis code comparison has been performed led by students. Binary evolution studies of potential progenitors show that there is a clear lack of understanding of the different paths that potentially lead to type Ia explosions and that they occur more often in nature that in the models. These studies are complemented by observational studies of potential pre-supernova X-ray emission potentially directly identifying progenitors (which was not found) and studies of the properties of type Ia supernova remnants (that suggest significant pre-supernova mass loss in the Kepler and possibly Tycho supernova systems). Finally, the Galactic center remains a focus of attention for the study of accretion onto super-massive black holes.

 

Network 3 members:

 Dr. A.L.Watts (chair) UvA
Prof.dr. B. Achterberg RU
Dr. D. Berge UvA
Prof.dr. H.Falcke RU
Prof.dr. P. Groot RU
Dr. J.W.T. Hessels UvA
Dr. J.R. Hörandel RU
Prof.dr. M. van der Klis UvA
Dr. E. Körding RU
Dr. S.B. Markoff UvA
Prof.dr. R.M. Mendez RUG
Dr. S. de Mink (nw 2 & nw3) UvA
Dr. S. Nissanke RU
Prof.dr. G. Nelemans RU
Dr. O. Pols RU
Prof.dr. S. Portegies Zwart UL
Dr. E.M. Rossi (nw1 & nw2) UL
Dr. A. Rowlinson UvA
Dr. P. Uttley UvA
Prof.dr. F. Verbunt RU
Dr. J. Vink UvA
Prof.dr. R.A.M.J. Wijers UvA
Dr. R. Wijnands UvA