[Depfis] Miércoles 20/3 14hs: Coloquio IAFE

[Andrea P. Buccino]

MIÉRCOLES 20 de marzo, 14hs
Aula del Edificio IAFE

"Black Holes at cosmic dawn: Impact in Cosmology and Gravitational-Wave 
Astrophysics"

  Dr. Felix Mirabel

Theoretical models and observations suggest that the first Black Holes 
(BHs) formed in the universe, namely, the remnants of the most massive 
primordial stars (Pop III stars), were prolifically formed in High Mass 
X-ray Binaries (HMXBs) of Pop III (Mirabel et al. 2011).  BH-HMXBs are 
also called Microquasars (MQs); besides radiation in the X-rays and 
gamma-rays (Mirabel 2012), MQs produce powerful synchrotron relativistic 
jets and massive outflows (Mirabel & Rodriguez 1994; 1998; 1999).

Two possible observational signatures of synchrotron radio emission 
from that putative large population of BH-HMXB-MQs at cosmic dawn may 
have been found recently. (1) A smooth cosmic radio background (CRB) of 
synchrotron spectrum but of unknown origin reported from ARCADE 2 
observations (Fixsen et al. 2011); and (2) A deep absorption in the rest 
frame 21cm transition of atomic hydrogen (HI) observed by EDGES, 
centered at redshift z=17, with an amplitude of the absorption profile 
more than twice the largest predictions (Bowman et al. 2018). The 
enhanced global absorption signal observed by EDGES could be due to 
excess radiation from a smooth Cosmic Radio Background (CRB), like the 
one reported with ARCADE 2.

The most likely sources of a very early smooth synchrotron CRB are the 
powerful relativistic jets from BHs formed by direct collapse, with no 
SNe (Mirabel & Rodrigues 2003) in BH-HMXB-MQs of Pop III. These are the 
first formed compact remnants of the most massive stars of Pop III, 
which precede supernova (SN) explosions, the formation of neutron stars, 
and dust.

BH-HMXB-MQs of Pop III promptly inject hard X-rays and relativistic 
jets into the IGM, which overtake the slowly expanding HII regions 
produced by the UV radiation of their progenitor Pop III stars, 
pre-heating and partially ionizing the IGM over larger distance scales. 
In this context BH-HMXB-MQs determine the early thermal history of the 
universe, the properties of the faintest galaxies at high redshifts, and 
the smallest dwarf galaxies in the local universe.

BH-HMXBs in the early universe are also of topical interest for the 
incipient Gravitational Waves Astrophysics. BH-HMXBs are channels for 
the formation of stellar binary black holes (BBHs; Mirabel 2017), the 
first detected sources of gravitational waves (GWs) produced when BBHs 
merge. The large masses of up to 40 solar masses of those merging BHs, 
relative to the masses of stellar BHs identified from X-ray observations 
in the Local Universe, and the high merging rates of BBHs found by the 
LIGO-Virgo collaboration, can naturally be accounted for in the context 
of the hypothesis of a high formation rate of BH-HMXBs and BBHs at 
cosmic dawn. A review of this work is in press (Mirabel 2019).

References:
Bowman, J.D., Rogers, A.E E., Monsalve, R.A. et al. 2018, Nature, 555, 
67
Fixsen D.J., Kogut A., Levin, S. etal. 2011, ApJ, 734, 5
Mirabel, I.F. & Rodriguez, L.F. 1994, Nature, 371, 46
Mirabel, I.F. & Rodriguez, L.F. 1998, Nature, 392, 673-677
Mirabel, I.F. & Rodriguez, L.F. 1999, ARAA, 37, 409-443
Mirabel, I.F. & Rodrigues, I. 2003, Science, 300, 1119
Mirabel, I.F., Dijkstra, M., Loeb, A., Laurent, Ph., Pritchard, D. 
2011, A&A, 528, A149
Mirabel, I.F. 2012, Science, 335, 175
Mirabel, I.F. 2017, New Astron. Revs. 78, 1
Mirabel, I.F. 2019, Invited review. Proceedings the IAU Symp. 346, in 
press: arXiv#1902.00511.pdf

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Andrea Paola Buccino
URL (Home Page): http://cms.iafe.uba.ar/abuccino
e-mail: abuccino en iafe.uba.ar
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