1,582 research outputs found
Probing the formation of the seeds of supermassive black holes with gravitational waves
The existence of black holes in the intermediate mass interval between one
hundred and ten thousand solar masses, filling the gap between the stellar and
the supermassive black holes is a key prediction to explain the origin of
luminous QSOs at redshifts as large as seven. There is a sheer difficulty in
forming giant black holes of billion suns in less than one billion years. This
has led to the concept of seed black holes. They are high redshift intermediate
mass black holes that formed during cosmic dawn. Seeds are a transient
population, which later grew massive through episodes of accretion and mergers.
In this chapter we explore the possibility of discovering seed black holes and
track their growth across all cosmic epoch, by detecting the gravitational wave
signal they emit at the time of their coalescence, when they pair to form close
binaries. We show that the ESA LISA mission for the detection of low frequency
gravitational waves will be paramount in granting this insight. Gravitational
waves travel unimpeded through the cosmos and carry exquisite information on
the masses and spins of the merging black holes. To this purpose we introduce
key concepts on the gravitational wave emission from binaries, describing
briefly their formation pathway during halo mergers and galaxy collisions.Comment: Preprint of a review volume chapter to be published in Latiff, M.,
and Schleicher, D. entitled Probing the formation of the seeds of
supermassive black holes with gravitational waves. Volume title: Formation of
the First Black Holes, 2018. Copyright World Scientific Publishing Company -
link - https://www.worldscientific.com/worldscibooks/10.1142/1065
Massive Binary Black Holes in the Cosmic Landscape
Binary black holes occupy a special place in our quest for understanding the
evolution of galaxies along cosmic history. If massive black holes grow at the
center of (pre-)galactic structures that experience a sequence of merger
episodes, then dual black holes form as inescapable outcome of galaxy assembly.
But, if the black holes reach coalescence, then they become the loudest sources
of gravitational waves ever in the universe. Nature seems to provide a pathway
for the formation of these exotic binaries, and a number of key questions need
to be addressed: How do massive black holes pair in a merger? Depending on the
properties of the underlying galaxies, do black holes always form a close
Keplerian binary? If a binary forms, does hardening proceed down to the domain
controlled by gravitational wave back reaction? What is the role played by gas
and/or stars in braking the black holes, and on which timescale does
coalescence occur? Can the black holes accrete on flight and shine during their
pathway to coalescence? N-Body/hydrodynamical codes have proven to be vital
tools for studying their evolution, and progress in this field is expected to
grow rapidly in the effort to describe, in full realism, the physics of stars
and gas around the black holes, starting from the cosmological large scale of a
merger. If detected in the new window provided by the upcoming gravitational
wave experiments, binary black holes will provide a deep view into the process
of hierarchical clustering which is at the heart of the current paradigm of
galaxy formation. They will also be exquisite probes for testing General
Relativity, as the theory of gravity. The waveforms emitted during the
inspiral, coalescence and ring-down phase carry in their shape the sign of a
dynamically evolving space-time and the proof of the existence of an horizon.Comment: Invited Review to appear on Advanced Science Letters (ASL), Special
Issue on Computational Astrophysics, edited by Lucio Maye
Unveiling black holes ejected from globular clusters
Was the black hole in XTE J1118+480 ejected from a globular cluster or kicked
away from the galactic disk?Comment: 2 pages, newpasp.sty. To appear in "New Horizons in Globular Cluster
Astronomy", eds. G. Piotto, G. Meylan, G.Djorgovski, M. Riell
LISA double black holes: Dynamics in gaseous nuclear discs
We study the inspiral of double black holes, with masses in the LISA window
of detectability, orbiting inside a massive circum-nuclear disc. Using
high-resolution SPH simulations, we follow the black hole dynamics in the early
phase when gas-dynamical friction acts on the black holes individually, and
continue our simulation until they form a close binary. We find that in the
early sinking the black holes lose memory of their initial orbital eccentricity
if they co-rotate with the gaseous disc, forming a binary with a low
eccentricity, consistent with zero within our numerical resolution limit. The
cause of circularization resides in the rotation present in the gaseous
background where dynamical friction operates. Circularization may hinder
gravitational waves from taking over and leading the binary to coalescence. In
the case of counter-rotating orbits the initial eccentricity does not decrease,
and the black holes may bind forming an eccentric binary. When dynamical
friction has subsided, for equal mass black holes and regardless their initial
eccentricity, angular momentum loss, driven by the gravitational torque exerted
on the binary by surrounding gas, is nevertheless observable down to the
smallest scale probed. In the case of unequal masses, dynamical friction
remains efficient down to our resolution limit, and there is no sign of
formation of any ellipsoidal gas distribution that may further harden the
binary. During inspiral, gravitational capture of gas by the black holes occurs
mainly along circular orbits: eccentric orbits imply high relative velocities
and weak gravitational focusing. Thus, AGN activity may be excited during the
black hole pairing process and double active nuclei may form when
circularization is completed, on distance-scales of tens of pcs.Comment: Minor changes, accepted to MNRAS (11 pags, 14 figs). Movies (.avi)
are available at http://pitto.mib.infn.it/~haardt/MOVIES
Is NGC6752 hiding a double black hole binary in its core ?
NGC6752 hosts in its halo PSR J1911-5958A, a newly discovered binary
millisecond pulsar which is the most distant pulsar ever known from the core of
a globular cluster. Interestingly, its recycling history seems in conflict with
a scenario of ejection resulting from ordinary stellar dynamical encounters. A
scattering event off a binary system of two black holes with masses in the
range of 3-50 solar masses that propelled PSR J1911-5958A into its current
peripheral orbit seems more likely. It is still an observational challenge to
unveil the imprint(s) left from such a dark massive binary on cluster's stars:
PSR J1911-5958A may be the first case.Comment: 2 pages, newpasp.sty. To appear in "New Horizons in Globular Cluster
Astronomy", eds. G. Piotto, G. Meylan, G.Djorgovski, M. Riell
On tilted Giraud subcategories
Firstly we provide a technique to move torsion pairs in abelian categories via adjoint functors and in particular through Giraud subcategories. We apply this point in order to develop a correspondence between Giraud subcategories of an abelian category C and those of its tilt H(C) i.e., the heart of a t-structure on the derived category D(C)i nduced by a torsion pair
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