The imprint of massive black hole formation models on the LISA data stream

The formation, merging and accretion history of massive black holes (MBHs) along the hierarchical build-up of cosmic structures leaves a unique imprint on the background of gravitational waves (GWs) at mHz frequencies. We study here, by means of dedicated simulations of black hole build-up, the possibility of constraining different models of black hole cosmic evolution using future GW space-borne missions, such as LISA . We consider two main scenarios for black hole formation, namely, one where seeds are light (  ≃10² M_⊙  , remnant of Population III stars) and one where seeds are heavy (  ≳10⁴ M_⊙  , direct collapse). In all the models we have investigated, MBH binary coalescences do not produce a stochastic GW background, but rather, a set of individual resolved events. Detection of several hundreds merging events in a 3-yr LISA mission will be the sign of a heavy seed scenario with efficient formation of black hole seeds in a large fraction of high-redshift haloes. At the other extreme, a low event rate, about a few tens in 3 yr, is peculiar of scenarios where either the seeds are light, and many coalescences do not fall into the LISA band, or seeds are massive, but rare. In this case a decisive diagnostic is provided by the shape of the mass distribution of detected events. Light binaries  ( m < 10⁴ M_⊙)  are predicted in a fairly large number in Population III remnant models, but are totally absent in direct collapse models. Finally, a further, helpful diagnostic of black hole formation models lies in the distribution of the mass ratios in binary coalescences. While heavy seed models predict that most of the detected events involve equal-mass binaries, in the case of light seeds, mass ratios are equally distributed in the range 0.1–1.     

黑洞吸积理论及其天体物理学应用的近期发展(Ⅰ)

黑洞吸积理论是天体物理学的一个基础理论,是认识许多高能天体系统,如活动星系核、黑洞X射线双星、伽马射线暴等的重要物理基础。该文评述了近年来黑洞吸积理论,尤其是径移主导吸积流(advection-dominated accretion flow,ADAF)模型及其变种的主要发展,并介绍该理论在银河系中心、低光度活动星系核、黑洞X射线双星等方面的应用。全文分为两篇,该文是第一篇,内容是关于黑洞的热吸积流理论及其在银河系中心的应用。     

Parallel tracks in infrared versus X-ray emission in black hole X-ray transient outbursts: a hysteresis effect?

We report the discovery of a new hysteresis effect in black hole X-ray binary state transitions, that of the near-infrared (NIR) flux (which most likely originates in the jets) versus X-ray flux. We find, looking at existing data sets, that the IR emission of black hole X-ray transients appears to be weaker in the low/hard state rise of an outburst than the low/hard state decline of an outburst at a given X-ray luminosity. We discuss how this effect may be caused by a shift in the radiative efficiency of the inflowing or outflowing matter, or variations in the disc viscosity or the spectrum/power of the jet. In addition we show that there is a correlation (in slope but not in normalization) between IR and X-ray luminosities on the rise and decline, for all three low-mass black hole X-ray binaries with well-sampled IR and X-ray coverage:   L _NIR∝ L ^0.5–0.7_X  . In the high/soft state this slope is much shallower;   L _NIR∝ L ^0.1–0.2_X  , and we find that the NIR emission in this state is most likely dominated by the viscously heated (as opposed to X-ray heated) accretion disc in all three sources.     

The Steep Balmer Decrement of Quasars and Seyfert I Galaxies and its Origin

Observations of QSOs and Seyfert I galaxies show an anomalously steep Balmer decrement, which is in contradiction to the prediction of the traditional recombination theory. This is a long standing puzzle in past three decades in the study of AGNs. In this paper, we provide an alternative approach to solve this puzzle by using a newly recognized line emission mechanism, namely, the “Cerenkov line-like radiation”. For this purpose, we collected about a hundred of QSOs and Seyfert I galaxies, whose Balmer decrements have been measured and published in the past 30 years, and make the theoretical calculations on the observed Balmer decrements using an improved formula for the Cerenkov line intensity. The agreement between the calculations and observations is excellent. Therefore, we argue that the broad hydrogen lines of the QSOs and Seyfert I galaxies mainly originate from the Cerenkov line-like radiation of relativistic electrons. If this suggestion is further confirmed, our knowledge about the physics of AGNs will be greatly changed.     

Ecotoxicity of Cadmium to Maize and Soybean Seedling in Black Soil

Ecotoxicity and bioavailability of cadmium(Cd)to the maize(Zea mays L.)and the soybean(Glycine max(L.)Merr.)were investigated by acute toxicity experiment in the laboratory with black soil.Ecotoxicity and bioavailability of Cd were quantified by calculating the median effective concentration(EC50)and bioaccumulation factor(BAF).The measurement endpoints used were seed germination and seedling growth(shoot and root).The results showed that concentrations of Cd in the soil had adverse effect on the growth of roots and shoots.Seed germination was not the sensitive indicator for the ecotoxicity of Cd in the soil,while the growth of roots was the most sensitive measurement endpoint.Absorbability and transport of Cd in plants depended on the test crop species and Cd concentrations in the soil.The maize retains more Cd in its roots,while the soybean transports more Cd to the shoots from roots.     

Variability of black hole accretion discs: the cool, thermal disc component

We extend the model of King et al. for variability in black hole accretion discs by taking proper account of the thermal properties of the disc. Because the degree of variability in the King et al. model depends sensitively on the ratio of disc thickness to radius, H / R , it is important to follow the time dependence of the local disc structure as the variability proceeds. In common with previous authors, we develop a one-zone model for the local disc structure. We agree that radial heat advection plays an important role in determining the inner disc structure, and also find limit-cycle behaviour. When the stochastic magnetic dynamo model of King et al. is added to these models, we find similar variability behaviour to before.
We are now better placed to put physical constraints on model parameters. In particular, we find that in order to be consistent with the low degree of variability seen in the thermal disc component of black hole binaries, we need to limit the energy density of the poloidal field that can be produced by local dynamo cells in the disc to less than a few per cent of the energy density of the dynamo field within the disc itself.