Three-Body Kick to a Bright Quasar out of Its Galaxy During a Merger

The quasar HE0450-2958 was recently discovered to reside ~7kpc away from a galaxy that was likely disturbed by a recent merger. The lack of a massive spheroid of stars around the quasar raised the unlikely suggestion that it may have formed in a dark galaxy. Here we explain this discovery as a natural consequence of a dynamical kick imparted to the quasar as it interacted with a binary black hole system during a galaxy merger event. The typical stalling radius for a ~10^9 solar mass binary provides a kick of order the escape velocity of the stellar spheroid, bringing the quasar out to around the observed radius before it turns around. This is consistent with the observed low relative velocity between the quasar and the merger-remnant galaxy. The gas carried with the black hole throughout the three-body interaction fuels the quasar for the duration of its journey, ~2x10^7 years. Gravitational radiation recoil could not have produced the required kick.Comment: 5 pages, 2 figures, ApJ Letters, in pres

Localizing Sagittarius A* and M87 on Microarcsecond Scales with Millimeter VLBI

With the advent of the Event Horizon Telescope (EHT), a millimeter/sub-millimeter very-long baseline interferometer (VLBI), it has become possible to image a handful of black holes with sub-horizon resolutions. However, these images do not translate into microarcsecond absolute positions due to the lack of absolute phase information when an external phase reference is not used. Due to the short atmospheric coherence time at these wavelengths, nodding between the source and phase reference is impractical. However, here we suggest an alternative scheme which makes use of the fact that many of the VLBI stations within the EHT are arrays in their own right. With this we show that it should be possible to absolutely position the supermassive black holes at the centers of the Milky Way (Sgr A*) and M87 relative to nearby objects with precisions of roughly 1 microarcsecond. This is sufficient to detect the perturbations to Sgr A*'s position resulting from interactions with the stars and stellar-mass black holes in the Galactic cusp on year timescales, and severely constrain the astrophysically relevant parameter space for an orbiting intermediate mass black hole, implicated in some mechanisms for producing the young massive stars in the Galactic center. For M87, it allows the registering of millimeter images, in which the black hole may be identified by its silhouette against nearby emission, and existing larger scale radio images, eliminating present ambiguities in the nature of the radio core and inclination, opening angle, and source of the radio jet.Comment: 18 pages, 4 figures, Accepted for publication in Ap

Gravitational waves from coalescing binaries and Doppler experiments

Doppler tracking of interplanetary spacecraft provides the only method presently available for broad-band searches of low frequency gravitational waves. The instruments have a peak sensitivity around the reciprocal of the round-trip light-time T of the radio link connecting the Earth to the space-probe and therefore are particularly suitable to search for coalescing binaries containing massive black holes in galactic nuclei. A number of Doppler experiments -- the most recent involving the probes ULYSSES, GALILEO and MARS OBSERVER -- have been carried out so far; moreover, in 2002-2004 the CASSINI spacecraft will perform three 40 days data acquisition runs with expected sensitivity about twenty times better than that achieved so far. Central aims of this paper are: (i) to explore, as a function of the relevant instrumental and astrophysical parameters, the Doppler output produced by in-spiral signals -- sinusoids of increasing frequency and amplitude (the so-called chirp); (ii) to identify the most important parameter regions where to concentrate intense and dedicated data analysis; (iii) to analyze the all-sky and all-frequency sensitivity of the CASSINI's experiments, with particular emphasis on possible astrophysical targets, such as our Galactic Centre and the Virgo Cluster.Comment: 52 pages, LaTeX, 19 Postscript Figures, submitted to Phys. Rev.

Menus for Feeding Black Holes

Black holes are the ultimate prisons of the Universe, regions of spacetime where the enormous gravity prohibits matter or even light to escape to infinity. Yet, matter falling toward the black holes may shine spectacularly, generating the strongest source of radiation. These sources provide us with astrophysical laboratories of extreme physical conditions that cannot be realized on Earth. This chapter offers a review of the basic menus for feeding matter onto black holes and discusses their observational implications.Comment: 27 pages. Accepted for publication in Space Science Reviews. Also to appear in hard cover in the Space Sciences Series of ISSI "The Physics of Accretion onto Black Holes" (Springer Publisher

Super-massive binary black holes and emission lines in active galactic nuclei

The broad emission spectral lines emitted from AGNs are our main probe of the geometry and physics of the broad line region (BLR) close to the SMBH. There is a group of AGNs that emits very broad and complex line profiles, showing two displaced peaks, one blueshifted and one redshifted from the systemic velocity defined by the narrow lines, or a single such peak. It has been proposed that such line shapes could indicate a supermassive binary black hole (SMB) system. We discuss here how the presence of an SMB will affect the BLRs of AGNs and what the observational consequences might be. We review previous claims of SMBs based on broad line profiles and find that they may have non-SMB explanations as a consequence of a complex BLR structure. Because of these effects it is very hard to put limits on the number of SMBs from broad line profiles. It is still possible, however, that unusual broad line profiles in combination with other observational effects (line ratios, quasi-periodical oscillations, spectropolarimetry, etc.) could be used for SMBs detection. Some narrow lines (e.g., [O\,III]) in some AGNs show a double-peaked profile. Such profiles can be caused by streams in the Narrow Line Region (NLR), but may also indicate the presence of a kilo-parsec scale mergers. A few objects indicated as double-peaked narrow line emitters are confirmed as kpc-scale margers, but double-peaked narrow line profiles are mostly caused by the complex NLR geometry. We briefly discuss the expected line profile of broad Fe K$\alpha$ that probably originated in the accretion disk(s) around SMBs. Finally we consider rare configurations where a SMB system might be gravitationally lensed by a foreground galaxy, and discuss the expected line profiles in these systems.Comment: The work was presented as an invited talk at special workshop "Spectral lines and super-massive black holes" held on June 10, 2011 as a part of activity within the frame of COST action 0905 "Black holes in a violent universe" and as a part of the 8th Serbian Conference on Spectral Line Shapes in Astrophysics.Sent to New Astronomy Review as a review pape

Balancing repair and tolerance of DNA damage caused by alkylating agents

Alkylating agents constitute a major class of frontline chemotherapeutic drugs that inflict cytotoxic DNA damage as their main mode of action, in addition to collateral mutagenic damage. Numerous cellular pathways, including direct DNA damage reversal, base excision repair (BER) and mismatch repair (MMR), respond to alkylation damage to defend against alkylation-induced cell death or mutation. However, maintaining a proper balance of activity both within and between these pathways is crucial for a favourable response of an organism to alkylating agents. Furthermore, the response of an individual to alkylating agents can vary considerably from tissue to tissue and from person to person, pointing to genetic and epigenetic mechanisms that modulate alkylating agent toxicity

Doet extreme droogte stikstofbom in droge heide barsten?

In oude heide is veel koolstof en stikstof vastgelegd in de organische bodemlagen. Zelfs sterk verhoogde stikstoftoevoer doet het heidesysteem nauwelijks lekken: er spoelt ook dan vrijwel geen nitraat of ammonium uit naar dieper grondwater. Echter, ernstige verstoringen zijn een risico voor het vrijkomen van deze stikstof, zoals extreme droogte. Om dit te onderzoeken is een laboratoriumexperiment uitgevoerd, aangevuld met veldmetingen na de extreem droge zomer van 2018. Het blijkt dat de N-huishouding ernstig verstoord is door extreme droogte met zeer hoge concentraties beschikbaar ammonium en veel nitraatuitspoeling als gevolg

Grip op beekslib : hoe meer aandacht voor slib de KRW-doelen dichterbij kan brengen

In veel beken worden ecologische KRW- en Natura2000-doelen voor waterplanten en vegetatie niet gehaald. De meeste doelsoorten prefereren matig voedselrijke omstandigheden, soms in combinatie met zacht, bicarbonaatarm water. Hoewel de fosfaatconcentratie in het oppervlaktewater van beken wel omlaag gebracht is, heeft dit op plekken met slibophoping niet geleid tot voldoende verbetering. Woekerende waterplanten kunnen gebruik maken van nutriënten en koolstof uit het slib, waarmee ze door hun snelle groei een betere concurrentiepositie hebbenten opzichte van veel doelsoorten. Dit vraagt om een aanpak waarin de rol van slib erkend wordt en sedimentatie van voedselrijk slib in beken wordt verminderd

Doet extreme droogte stikstofbom in droge heide barsten?

In oude heide is veel koolstof en stikstof vastgelegd in de organische bodemlagen. Zelfs sterk verhoogde stikstoftoevoer doet het heidesysteem nauwelijks lekken: er spoelt ook dan vrijwel geen nitraat of ammonium uit naar dieper grondwater. Echter, ernstige verstoringen zijn een risico voor het vrijkomen van deze stikstof, zoals extreme droogte. Om dit te onderzoeken is een laboratoriumexperiment uitgevoerd, aangevuld met veldmetingen na de extreem droge zomer van 2018. Het blijkt dat de N-huishouding ernstig verstoord is door extreme droogte met zeer hoge concentraties beschikbaar ammonium en veel nitraatuitspoeling als gevolg

Middellange termijn effecten van chopperen en drukbegrazing als alternatieven voor plaggen op natte heide

Herstel van de habitatkwaliteit van natte heide is zowel op nationaal als op Europees niveau een belangrijke opgave. Dit vergt behalve hydrologisch herstel ook een zorgvuldige afweging tussen verschillende maatregelen voor vegetatiebeheer en herstel van buffercapaciteit (Wallis de Vries et al., 2016). Vanwege de ingrijpende invloed van plaggen op bodem, vegetatie en fauna zijn in dit onderzoek chopperen en drukbegrazing, al of niet in combinatie met bekalking, als mogelijke alternatieven onderzocht