Final Activity Report Summary - XRB-AGN Connections (Black hole accretion on all mass scales)
How similar are white dwarfs, neutron stars and black holes? While these objects are physically very different, they all interact with their surrounding gas mainly via gravity so their chemical composition does not play a major role. On earth we can only observe these sources because some gas is gravitationally attracted by the central mass and falls towards the object. This process, called accretion, liberates energy that is partially radiated in form of light. An intriguing phenomenon of most accreting sources is that one observes highly collimated streams of gas originating from the source. Thus, they do not only accrete matter, but a small fraction of the accreted matter is ejected again from the system in form of jets. The project was aimed to answer the question how similar accretion onto the different types of objects and their related jet phenomena are.
Accretion of matter onto a compact object is a common and extremely efficient source of energy. It powers active galactic nuclei (AGN), accreting black holes with masses that can reach billions of solar masses. Also stellar mass objects, like neutron star and black hole X-ray binaries (XRBs) but also white dwarfs are also thought to be powered by accretion. In this project we have found that all these objects can be described by a common model describing the coupling between the jet and the accretion disc.
Prior to this project the unified model has been proposed for black hole X-ray binaries. We have been able to extend it to AGN by showing that all black holes follow correlations between their black hole masses, their accretion rate and X-ray luminosity or their timing properties. We also showed that their outburst cycle is likely to be similar to XRBs by generalising the hardness-intensity diagrams used for XRBs.
It is generally assumed that AGN have a strong influence on the structure formation in our Universe. However, those AGN that are responsible for this process are extremely far away from us and thus hard to observe. We have therefore scaled our model established for local XRBs and AGN to the AGN found in the distant universe. We were able to calculate the total power created by AGN available to influence the structure formation.
Finally, we showed that also white dwarfs can be included in the unified model. For the first time we have shown that dwarf novae, a type of accreting non-magnetic white dwarfs, also show jet. These jets follow the same disc/jet coupling as XRBs and also their strength relative to their accretion power is similar. Thus, we have found that accretion onto different types of objects indeed seems to follow a generic pattern.
Accretion of matter onto a compact object is a common and extremely efficient source of energy. It powers active galactic nuclei (AGN), accreting black holes with masses that can reach billions of solar masses. Also stellar mass objects, like neutron star and black hole X-ray binaries (XRBs) but also white dwarfs are also thought to be powered by accretion. In this project we have found that all these objects can be described by a common model describing the coupling between the jet and the accretion disc.
Prior to this project the unified model has been proposed for black hole X-ray binaries. We have been able to extend it to AGN by showing that all black holes follow correlations between their black hole masses, their accretion rate and X-ray luminosity or their timing properties. We also showed that their outburst cycle is likely to be similar to XRBs by generalising the hardness-intensity diagrams used for XRBs.
It is generally assumed that AGN have a strong influence on the structure formation in our Universe. However, those AGN that are responsible for this process are extremely far away from us and thus hard to observe. We have therefore scaled our model established for local XRBs and AGN to the AGN found in the distant universe. We were able to calculate the total power created by AGN available to influence the structure formation.
Finally, we showed that also white dwarfs can be included in the unified model. For the first time we have shown that dwarf novae, a type of accreting non-magnetic white dwarfs, also show jet. These jets follow the same disc/jet coupling as XRBs and also their strength relative to their accretion power is similar. Thus, we have found that accretion onto different types of objects indeed seems to follow a generic pattern.