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In recent numerical simulations (Matsubayashi et al. 2007;Löckmann, & Baumgardt 2008), it has been found that the eccentricity of supermassive black hole(SMBH) -intermediate black hole(IMBH) binaries grows toward unity through interactions with stellar background. This increase of eccentricity reduces the merging timescale of the binary through the gravitational radiation to the value well below the Hubble Time. It also gives the theoretical explanation of the existence of eccentric binary such as that in OJ287 (Lehto, & Valtonen 1996;Valtonen et al. 2008). In self-consistent N-body simulations, this increase of eccentricity is always observed. On the other hand, the result of scattering experiment between SMBH binaries and field stars (Quinlan 1996) indicated no increase of eccentricity. This discrepancy leaves the high eccentricity of the SMBH binaries in N-body simulations unexplained. Here we present a stellar-dynamical mechanism that drives the increase of the eccentricity of an SMBH binary with large mass ratio. There are two key processes involved. The first one is the Kozai mechanism under non-axisymmetric potential, which effectively randomizes the angular momenta of surrounding stars. The other is the selective ejection of stars with prograde orbits. Through these two mechanisms, field stars extract the orbital angular momentum of the SMBH binary. Our proposed mechanism causes the increase in the eccentricity of most of SMBH binaries, resulting in the rapid merger through gravitational wave radiation. Our result has given a definite solution to the "last-parsec problem"

The discovery of an intermediate-mass black hole (IMBH ) supports a runaway path of supermassive black hole (SMBH ) formation in galactic nuclei. No concrete model to explain all the steps of this bottom-up scenario for SMBHs is yet known, but here we propose to use gravitational radiation to probe the merging history of IMBHs. Collisions of black holes of mass 10 3 -10 6 M will produce gravitational radiation of 10 À1 to 10 2 Hz in their final merging phase. We assume that a thousand 10 3 M IMBHs form a 10 6 M black hole in each galaxy via two different merging histories-hierarchical growth and monopolistic growth-using a theoretical model of quasar formation having a peak at z ' 2:5. We find that there would be 22-67 IMBH merging events per year in the universe and that the event numbers of the two models apparently differ in the frequency of gravitational radiation. Most of the bursts by these events will be detectable by currently proposed space gravitational wave antennas, such as LISA or DECIGO. We conclude that the statistics of the signals would provide both a galaxy distribution and a formation model of SMBHs. Subject heading gs: black hole physics -gravitational waves 864

Based on the gamma-ray burst event rate at redshifts of , which is assessed by the spectral peak 4 ≤ z ≤ 12 energy-to-luminosity relation recently found by Yonetoku et al., we observationally derive the star formation rate (SFR) for Population III (Pop. III) stars in a high-redshift universe. As a result, we find that Pop. III stars could form continuously at . Using the derived Pop. III SFR, we attempt to estimate the ultraviolet (UV) 4 ≤ z ≤ 12 photon emission rate at in which redshift range no observational information has been hitherto obtained 7 ≤ z ≤ 12 on ionizing radiation intensity. We find that the UV emissivity at can make a noticeable contribution 7 ≤ z ≤ 12 to the early reionization. The maximal emissivity is higher than the level required to keep ionizing the intergalactic matter (IGM) at . However, if the escape fraction of ionizing photons from Pop. III objects is smaller 7 ≤ z ≤ 12 than 10%, then the IGM can be neutralized at some redshift, which may lead to the double reionization. As for the enrichment, the ejection of all metals synthesized in Pop. III objects is marginally consistent with the IGM metallicity, although the confinement of metals in Pop. III objects can reduce the enrichment significantly.

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