4 research outputs found
Investigating the retention of intermediate-mass black holes in star clusters using N-body simulations
Contrary to supermassive and stellar-mass black holes (SBHs), the existence
of intermediate-mass black holes (IMBHs) with masses ranging between 10^{2-5}
Msun has not yet been confirmed. The main problem in the detection is that the
innermost stellar kinematics of globular clusters (GCs) or small galaxies, the
possible natural loci to IMBHs, are very difficult to resolve. However, if
IMBHs reside in the centre of GCs, a possibility is that they interact
dynamically with their environment. A binary formed with the IMBH and a compact
object of the GC would naturally lead to a prominent source of gravitational
radiation, detectable with future observatories. We use N-body simulations to
study the evolution of GCs containing an IMBH and calculate the gravitational
radiation emitted from dynamically formed IMBH-SBH binaries and the possibility
that the IMBH escapes the GC after an IMBH-SBH merger. We run for the first
time direct-summation integrations of GCs with an IMBH including the dynamical
evolution of the IMBH with the stellar system and relativistic effects, such as
energy loss in gravitational waves (GWs) and periapsis shift, and gravitational
recoil. We find in one of our models an intermediate mass-ratio inspiral
(IMRI), which leads to a merger with a recoiling velocity higher than the
escape velocity of the GC. The GWs emitted fall in the range of frequencies
that a LISA-like observatory could detect, like the European eLISA or in
mission options considered in the recent preliminary mission study conducted in
China. The merger has an impact on the global dynamics of the cluster, as an
important heating source is removed when the merged system leaves the GC. The
detection of one IMRI would constitute a test of GR, as well as an irrefutable
proof of the existence of IMBHs.Comment: Accepted for publication by A&A, minor modification
Ultrafast Pulse Radiolysis Using a Terawatt Laser Wakefield Accelerator
We report the first ultrafast pulse radiolysis transient absorption
spectroscopy measurements from the Terawatt Ultrafast High Field Facility
(TUHFF) at Argonne National Laboratory. TUHFF houses a 20 TW Ti:sapphire laser
system that generates 2.5 nC sub-picosecond pulses of multi-MeV electrons at 10
Hz using laser wakefield acceleration. The system has been specifically
optimized for kinetic measurements in a pump-probe fashion. This requires
averaging over many shots which necessitates stable, reliable generation of
electron pulses. The latter were used to generate excess electrons in pulse
radiolysis of liquid water and concentrated solutions of perchloric acid. The
hydronium ions in the acidic solutions react with the hydrated electrons
resulting in the rapid decay of the transient absorbance at 800 nm on the
picosecond time scale. Time resolution of a few picoseconds has been
demonstrated. The current time resolution is determined primarily by the
physical dimensions of the sample and the detection sensitivity. Subpicosecond
time resolution can be achieved by using thinner samples, more sensitive
detection techniques and improved electron beam quality.Comment: submitted to J. Appl. Phys. 5 figures, 23 page
Subpicosecond radiolysis by means of terawatt laser wakefield accelerator
This is the publisher's version, also available electronically from http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=1274463A novel subpicosecond pulse radiolysis experimental system has been developed in Terawatt Ultrafast High Field Facility (TUHFF) at Argonne National Laboratory. TUHFF houses a 20 TW Ti:sapphire laser system that generates 2.5 nC sub-picosecond pulses of 4-25 MeV electrons at 10 Hz using laser wakefield acceleration. The system has been optimized for chemical studies. The subpicosecond electron pulses were used to generate hydrated electrons in pulse radiolysis of liquid water. Preliminary transient absorption spectroscopy data with picosecond resolution is presented