TASER

Timing And Spectroscopy in the Eddington Regime

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 Obiettivo del progetto (Objective)

'The process of accretion onto black holes is well studied at sub-Eddington rates, but as the flow approaches the Eddington limit for spherical accretion, our understanding breaks down. This project seeks to investigate the properties of accretion in the Eddington-regime using the latest advanced spectral-timing methods. These will provide a hitherto unseen view of accretion at extreme rates, the nature of which will have important consequences for our view of quasar growth in the early universe and the behaviour of outflows seen to originate from these bright accreting sources. The project will incorporate the vast quantities of excellent data available for Eddington rate X-ray binaries (XRBs) and also include the available high-quality data for Eddington rate active galactic nuclei (AGN) and ultra-luminous X-ray sources (ULXs). Such a wide survey of properties of Eddington-regime objects has never been undertaken, yet the broad range of masses incorporated into the sample will reveal behaviours spanning many decades in scaled frequency and energy making for a complete characterisation of the regime. The broad survey will identify any patterns of variability originating from the global properties of Eddington accretion and may also identify the presence of instabilities with important consequences for our models describing the accretion flow. In searching for the signatures of uncollimated outflows, we will identify the physical properties of the wind and also the effect these have upon the observed variability properties. Due to the focus on timing behaviour and the significant quantity of XRB physics that will be required, the API at the University of Amsterdam is the natural host institution for this project as it benefits from having unparalleled group expertise which can provide the necessary, high level of training and development.'

Introduzione (Teaser)

Supermassive black holes (SMBHs) with masses over a billion times that of our Sun accumulated their mass more quickly than conventional theory can calculate. Scientists are analysing a large sample of similar cosmic systems to understand how this might have happened.

Descrizione progetto (Article)

Black holes (BHs) are the remnants of former stars that have collapsed upon themselves, becoming so dense and compact that not even light can escape their gravitational pull. BHs have a voracious appetite for other material in the Universe for the same reason and accrete it on a regular basis.

SMBHs include those in active galactic nuclei (AGN) at the centres of many galaxies, among them the Milky Way. They were full-grown very early on and their rapid accretion exceeds the classical limit (Eddington limit) imposed by the balance between gravity and liberated radiation.

SMBHs in AGN accrete over decades to millennia, making their study impractical. EU-funded scientists launched the project 'Timing and spectroscopy in the Eddington regime' (TASER) to conduct a comprehensive study of suitable analogues on faster time scales close to home.

Black-hole binaries (BHBs) are systems where a normal star orbits a black hole, feeding it material, which the black hole accretes. The black holes in these systems are only ten times more massive than our sun and these smaller BHs that accrete at or near the Eddington limit undergo changes on much smaller timescales than the supermassive black holes. The team set out to identify and study many of these and their joint time and energy (spectral) properties

Just prior to project initiation, the fellow discovered the first extragalactic microquasar in our nearest galaxy Andromeda. Microquasars are BHBs that spew out a powerful jet of plasma when accretion rates spike. Work showing that the microquasar accreted at close to Eddington rates led to a publication in the prestigious peer-reviewed journal Nature.

Subsequent studies investigated how the jet and inflow might couple together, a key component of Eddington accretion. The seminal work established that the phenomenon can in fact be studied with extragalactic microquasars in nearby galaxies, providing a larger sample population than found in the Milky Way.

This has opened the door to a comprehensive search for more extragalactic microquasars. In the meantime, researchers developed algorithms for analysis of the spectral and timing characteristics of those sources. The spectral-timing codes are expected to provide important insight into the nature of 'super-Eddington' accretion in BHs and thus shed light on the origins and evolution of the Universe.