Accreting compact stars and the evolution of structure in the Universe

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Ομιλητής :  
Δρ. Φίλιππος Κολιοπάνος (Obs. Midi-Pyrénées - IRAP, Γαλλία)
Αίθουσα :  
Online seminar
Ημερομηνία :  

Ώρα : 

Περίληψη :

Supermassive black holes (SMBHs) of millions to billions of solar masses lie in the centers of most (if not all) galaxies. As more and more evidence point towards the co-evolution between SMBHs and their host galaxies, the question of their formation becomes a key factor for understanding the evolution of the structure of our Universe as it is currently observed. The recent discoveries of SMBHs with a mass exceeding five hundred million solar masses at a redshift higher than 7.5, elevates this question into one of the most intriguing problems of modern astrophysics. Namely: How do these massive "Titans" form within less than seven hundred million years from the Big Bang? 

Since there is no direct progenitor for a million (or billion) solar mass black hole, SMBHs have to grow via accretion onto smaller seeds. Given the tight time constraints for their creation, SMBHs may grow in one of two ways: 1) Episodic supercritical accretion of mass onto "light" seeds of less than 1000Msol, at rates that exceed the limitations imposed by the balancing between the pressure of the accretion powered emission vs the pressure of the in-falling gas (i.e. the Eddington limit). 2) Moderate accretion onto massive seeds that form directly at the mass range of 105Msol.

In my talk I will discuss these questions, briefly review  the current observational and theoretical status and also present my own work and a long-term and ambitious future program through which I aim to address them. This work involves the entire mass range of compact objects, from SMBHs to ultraluminous neutron stars, spans the entire E/M band and attempts to tackle several open astrophysical problems, including accretion above the Eddington limit and the existence of the elusive Intermediate Mass Black Holes.