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

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

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

Is NGC 6752 Hosting a Single or a Binary Black Hole?

The five millisecond pulsars that inhabit NGC 6752 display locations or accelerations remarkably different with respect to all other pulsars known in globular clusters. This may reflect the occurrence of an uncommon dynamics in the cluster core that could be attributed to the presence of a massive perturber. We here investigate whether a single intermediate-mass black hole, lying on the extrapolation of the mass versus sigma relation observed in galaxy spheroids, or, a less massive black hole binary could play the requested role.Comment: To appear in "Carnegie Observatories Astrophysics Series, Vol. 1: Coevolution of Black Holes and Galaxies," ed. L. C. Ho (Pasadena: Carnegie Observatories, http://www.ociw.edu/ociw/symposia/series/symposium1/proceedings.html

Will a Black Hole Soon Emerge from SN 1997D ?

Observations combined with theoretical modeling of the light curve of the recently discovered supernova 1997D in NGC 1536 suggest that it might host a black hole formed in the aftermath of the explosion. We consider some observable consequences of a black hole in SN 1997D and estimate the late--time accretion luminosity of the material which falls back onto the hole. We find that this luminosity, decaying with a characteristic power--law dependence on time, may emerge above the emission of the envelope in just a few years. Its detection would thus provide unmistakable evidence for the presence of a black hole.Comment: 8 pages, LaTeX, aaspp4.sty style file (AASTEX package), 2 postscript figures (included). To appear in The Astrophysical Journal Letters (scheduled for August 1, 1998 issue, Vol. 502

Hydrodynamical simulations of the tidal stripping of binary stars by massive black holes

In a galactic nucleus, a star on a low angular momentum orbit around the central massive black hole can be fully or partially disrupted by the black hole tidal field, lighting up the compact object via gas accretion. This phenomenon can repeat if the star, not fully disrupted, is on a closed orbit. Because of the multiplicity of stars in binary systems, also binary stars may experience in pairs such a fate, immediately after being tidally separated. The consumption of both the binary components by the black hole is expected to power a double-peaked flare. In this paper, we perform for the first time, with GADGET2, a suite of smoothed particle hydrodynamics simulations of binary stars around a galactic central black hole in the Newtonian regime. We show that accretion luminosity light curves from double tidal disruptions reveal a more prominent knee, rather than a double peak, when decreasing the impact parameter of the encounter and when elevating the difference between the mass of the star which leaves the system after binary separation and the mass of the companion. The detection of a knee can anticipate the onset of periodic accretion luminosity flares if one of the stars, only partially disrupted, remains bound to the black hole after binary separation. Thus knees could be precursors of periodic flares, which can then be predicted, followed up and better modelled. Analytical estimates in the black hole mass range $10^5-10^8 \rm M_{\rm \odot}$ show that the knee signature is enhanced in the case of black holes of mass $10^6-10^7 \rm M_{\rm \odot}$.Comment: 14 pages, 6 figures, 8 tables. Accepted by MNRA

Radiation from the first forming stars

The evolution of radiation emitted during the dynamical collapse of metal-free protostellar clouds is investigated within a spherically symmetric hydrodynamical scheme that includes the transfer of radiation and the chemistry of the primordial gas. The cloud centre collapses on a time scale of about 10^5-10^6 years, thanks to line cooling from molecular hydrogen (H2). For most of the collapse time, when the evolution proceeds self-similarly, the luminosity slowly rises up to about 10^36 erg/s and is essentially due to H2 IR line emission. Later, continuum IR radiation provides an additional contribution, which is mostly due to the accretion of an infalling envelope upon a small hydrostatic protostellar core which develops in the centre. We follow the beginning of the accretion phase, when the enormous accretion rate (~ 0.1 Msun/yr) produces a very high continuum luminosity of about 10^36 erg/s. Despite the high luminosities, the radiation field is unable to affect the gas dynamics during the collapse and the first phases of accretion, because the opacity of the infalling gas is too small; this is quite different from present-day star formation. We also find that the protostellar evolution is similar among clouds with different initial configurations, including those resulting from 3D cosmological simulations of primordial objects; in particular, the shape of the molecular spectra is quite universal. Finally, we briefly discuss the detectability of this pristine cosmic star formation activity.Comment: 39 pages, 12 figures; revised version with major changes (including title) to appear in MNRA