arXiv subjects

Nicholas Chamberlain Stone

Publications and source records attributed to Nicholas Chamberlain Stone.

5 recordsLinked to original sources

arXiv2026

Anisotropic wind in tidal disruption events

Over the coming years, the number of tidal disruption events (TDEs) is expected to substantially increase with observations from the Vera Rubin Observatory (g and r band) and {\it ULTRASAT} (near UV) wide-field surveys. These future samples have great promise to characterize the bottom end of the massive black hole mass function, but existing detections of intermediate mass black hole TDEs are primarily in X-rays, leaving their optical/UV emission largely unexplored. We present a time- and angle-dependent analysis of the outflow produced by dissipation near pericentre in a three-dimensional end-to-end radiation-hydrodynamics simulation of a TDE by a $10^4 M_\odot$ black hole with realistic parameters, run with the code RICH. We find that outflow anisotropy produces viewing-angle-dependent observables. Towards the poles and the pericentre region, mass-loss rates are low and bolometric luminosities reach $\sim2$--$3$ times the Eddington luminosity. Towards the stream, the properties show a stronger dependence on latitude: the mass-loss rate increases and the bolometric luminosity decreases as the line of sight approaches the orbital plane. These denser regions favour H$\alpha$ and H$\beta$ emission. Despite these variations, all viewing directions show a common spectral evolution, with an initial soft X-ray flare followed (around $1.25t_{\rm fb}\approx3$~days) by the reprocessing of shock-powered emission into the UV and optical bands. Although the optical/UV luminosities we predict for this TDE are likely too dim for past surveys (e.g. ASAS-SN, ZTF), they are within the detection capabilities of LSST and ULTRASAT to horizons of $\sim 790$ and $\sim 340$ Mpc, respectively, for the brightest viewing directions.

astro-ph.HE↗

arXiv2025

Wind-mediated Eddington-limited emission in a $10^{4}M_\odot$ Black Hole Tidal Disruption Event

Observations of tidal disruption events (TDEs) have already produced tens of strong candidate flares, and their number will greatly increase with upcoming wide field surveys. Nevertheless, the origin of the measured luminosity peak at early times is still unknown, and the ultimate sources of energy dissipation in TDEs are not fully understood. Here we present the first three-dimensional end-to-end simulation of a TDE by a $10^{4}M_\odot$ intermediate mass black hole (IMBH) with realistic parameters, run with the radiation-hydrodynamics code RICH. We find that the stellar debris fails to circularize efficiently, while a low-density, radiation-driven wind forms near pericenter and expands quasi-spherically. Radiation is advected by this outflow and released at the photosphere, which expands to radii of $\approx10^{13}$ cm and reaches temperatures of ~few $10^{4}$K at the peak of the light curve. The resulting luminosity briefly exceeds the Eddington limit before settling near that value. We systematically test the numerical convergence of our simulation by running it at three resolutions. While the nozzle shock at pericenter may be under-resolved, we find that global results are qualitatively converged and, largely, quantitatively robust. The upcoming Vera Rubin Observatory's LSST (g and r band) and ULTRASAT (near UV) will be able to observe events like our simulated IMBH TDE up to redshifts of z$\approx$0.1 and z$\approx$0.06, respectively.

astro-ph.HE↗

arXiv2024

Boson Cloud Atlas: Direct mass measurements of superradiance clouds near black holes

Ultralight scalars emerge naturally in several motivated particle physics scenarios and are viable candidates for dark matter. While laboratory detection of such bosons is challenging, their existence in nature can be imprinted on measurable properties of astrophysical black holes (BHs). The phenomenon of superradiance can convert the BH spin kinetic energy into a bound cloud of scalars. In this letter, we propose a new technique for directly measuring the mass of a dark cloud around a spinning BH. We compare the measurement of the BH spin obtained with two independent electromagnetic techniques: continuum fitting and iron K$\alpha$ spectroscopy. Since the former technique depends on a dynamical observation of the BH mass while the latter does not, a mismatch between the two measurements can be used to infer the presence of additional extended mass around the BH. We find that a precision of $\sim 1\%$ on the two spin measurements is required to exclude the null hypothesis of no dark mass around the BH at a 2$\sigma$ confidence level for dark masses about a few percent of the BH mass, as motivated in some superradiance scenarios.

astro-ph.HE↗

arXiv2022

Revisiting Stellar Orbits and the Sgr A$^*$ Quadrupole Moment

The "no-hair" theorem can, in principle, be tested at the center of the Milky Way by measuring the spin and the quadrupole moment of Sgr A$^*$ with the orbital precession of S-stars, measured over their full periods. Contrary to the original method, we show why it is possible to test the no-hair theorem using observations from only a single star, by measuring precession angles over a half-orbit. There are observational and theoretical reasons to expect S-stars to spin rapidly, and we have quantified the effect of stellar spin, via spin-curvature coupling (the leading-order manifestation of the Mathisson-Papapetrou-Dixon equations), on future quadrupole measurements. We find that they will typically suffer from errors of order a few percentage points, but for some orbital parameters, the error can be much higher. We re-examine the more general problem of astrophysical noise sources that may impede future quadrupole measurements, and find that a judicious choice of measurable precession angles can often eliminate individual noise sources. We have derived optimal combinations of observables to eliminate the large noise source of mass precession, the novel noise of spin-curvature coupling due to stellar spin, and the more complicated noise source arising from transient quadrupole moments in the stellar potential.

astro-ph.GA↗

arXiv2018

A Generalised Bondi Accretion Model for the Galactic Centre

We develop an analytic, steady-state model for the gas environment in quiescent galactic nuclei. We assume that the mass is constantly supplied by a spherically symmetric distribution of wind emitting stars, and that gravity is solely due to a central supermassive black hole. We show that at some finite radius, where the Keplerian velocity is comparable to the wind velocity, the bulk velocity vanishes. Matter generated below that radius will be accreted onto the black hole, while matter outside it will escape the system. Under certain conditions, the flow may become supersonic at both domains. We obtain radial profiles of the hydrodynamic variables and verify them using a time-dependent hydrodynamic simulation. We delineate the conditions under which radiative cooling can be neglected, and predict the luminosity and spectrum of the free-free X-ray emission from such a system. We discuss applications of our solution to our own Galactic Centre and other quiescent galactic nuclei.

astro-ph.GA↗