research
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Probability that a star will produce a BH vs the star's initial mass. We derive this probability in two limits. In one we assume that the most massive stars explode as supernovae and produce neutron stars. In the other limit we do not place any restrictions on the massive stars.
Collaborators: Tony Piro and Christian Ott
All massive stars undergo core collapse at the end of their lives, but it is not known which stars will produce black holes instead of neutron stars as a result of this collapse. The mapping between initial stellar mass and neutron star vs. black hole formation is complicated by binarity, mass loss, metallicity, and perhaps even stochastic structural differences from star to star. Given these factors, we have argued for a probabilistic description of black hole formation. We have made a first attempt at deriving the black hole formation probability as a function of zero age main sequence mass using the mass distribution of black holes in X-ray binaires.
Related papers:
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Snapshot from a simulation of a 0.55 solar mass WD being tidally disrupted by a 10,000 solar mass BH.
Collaborators: Mike Eracleous, Steinn Sigurdsson, and Jimmy Irwin
When a star gets too close to a black hole, the tidal acceleration across its diameter exceeds its self gravity and it gets ripped apart. We have modeled the emission lines produced when the accretion flare produced by such events photoionizes a portion of the debris. The models combine dynamical models for the evolution of the debris (both analytic and SPH) with photoionization models. We’ve looked at the tidal disruption of white dwarfs (in both bound and unbound orbits) and horizontal branch stars by intermediate mass black holes.
Related papers and posters:
Clausen, Sigurdsson, Eracleous & Irwin, 2012, MNRAS, 424, 1268
Clausen & Eracleous, 2011, ApJ, 726, 34
"Tidal Disruption Events and AGN Outbursts" conference proceedings
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log g - log T diagram showing the evolution of a 0.6 solar mass star with a uniform composition of 60% helium by mass. The star is formed by the merger of a helium white dwarf with an M-dwarf and evolves to spend 210 Myr as a subdwarf.
Collaborators: Richard Wade, Richard O'Shaughnessy, Ravi Kopparapu, and Mike Eracleous
We’ve studied the formation of hot subdwarfs using fast binary evolution codes (e.g., Hurley et al.'s BSE) and Paxton et al.’s detailed stellar evolution code MESA Star. We’ve proposed a new formation channel for single subdwarfs that involves the merger of a helium white dwarf with an M-dwarf. Furthermore, our models suggest that the period distribution of F-dwarf + subdwarf binaries is useful in constraining binary evolution models.
Related papers:
Clausen & Wade, 2011, ApJL, 733, 42
Clausen, Wade, Kopparapu, & O'Shaughnessy, 2012, ApJ, 746, 186
We are also using fast binary evolution codes to explore whether observed properties of extragalactic X-ray binary populations can be understood given the present knowledge about binary evolution.
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Initial locations of the BH-NS binaries in the (1-e2 )-a plane. The gravitational radiation merger time is constant along the solid lines. From left to right, the lines correspond to 106, 108, 1010 yrs. Although many binaries are formed with merger times that are much longer than a Hubble time, subsequent interactions with stars in the cluster drive them to merge on much shorter time scales.
Collaborators: Steinn Sigurdsson & David Chernoff
In globular clusters the stars are so densely packed that they interact with each other. We’ve simulated interactions between BH-binaries and single stars to investigate the formation of BH-neutron star (BH-NS) binaries. We find that in dense, massive clusters, many of the BH-NS binaries formed by these encounters undergo gravitational radiation driven mergers. BHs retained by the cluster after merging with a NS can acquire subsequent NS companions and undergo several mergers. Systems that do not merge may be observable as BH-millisecond pulsar binaries. We have explored the distribution of orbital parameters in such binaries and the cluster properties that promote their formation.
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