Starfall: A heavy rain of stars in 'turning on' AGN

McKernan, B.; Ford, K. E. S.; Cantiello, M.; Graham, M. J.; Jermyn, A. S.; Leigh, N. W. C.; Ryu, T.; Stern, D.

doi:10.48550/arxiv.2110.03741

Cited by 6 publications

(12 citation statements)

References 46 publications

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“…Tidal disruptions may also occur in active galactic nuclei (e.g. Chan et al 2019Chan et al , 2020McKernan et al 2021), as hinted at by some observations (e.g. Blanchard et al 2017;Liu et al 2018Liu et al , 2020.…”

Section: Introductionmentioning

confidence: 82%

An Analytic, Fully Relativistic Framework for Tidal Disruption Event Streams in Schwarzschild Geometry

Dittmann

2021

Preprint

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We present an analytic and fully relativistic framework for studying the self-intersection of tidal disruption event (TDE) streams, restricting ourselves to the Schwarzschild spacetime. By taking advantage of the closed-form solution to the geodesic equations in the Schwarzschild metric, we calculate properties of the self-intersection without numerically evaluating the geodesic equations or making any post-Newtonian approximations. Our analytic treatment also facilitates geometric definitions of the orbital semi-major axis and eccentricity, as opposed to Newtonian formulas which lead to unphysical results for highly-relativistic orbits. Combined with assumptions about energy dissipation during the self-intersection shock, our framework enables the calculation of quantities such as the fraction of material unbound during the selfintersection shock, and the characteristic semi-major axes and eccentricities of the material which remains in orbit after the collision. As an example, we calculate grids of post-intersection properties in stellar and supermassive black hole (SMBH) masses for disruptions of main sequence stars, identifying regions where no material is ejected during self intersection (e.g. SMBH mass 5 × 10 6 M for 1 M stars disrupted at the tidal radius), potentially explaining the TDEs observed by SGR/eROSITA which are visible in X-rays but not optical wavelengths. We also identify parameters for which the post-intersection accretion flow has low eccentricity (𝑒 0.6), and find that the luminosity generated by self-intersection shocks only agrees with observed trends in the relationship between light curve decay timescales and peak luminosities over a narrow range of SMBH masses.

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Section: Introductionmentioning

confidence: 82%

An Analytic, Fully Relativistic Framework for Tidal Disruption Event Streams in Schwarzschild Geometry

Dittmann

2021

Preprint

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“…Their model suggests TDEs with mildly-relativistic outflows are likely important contributors to the cosmic neutrino flux, particularly at high energies, and also shows the key role that UV observations play in probing extreme AGN events, touching on AGN ( § 9), TDEs ( § 10), and multimessenger astrophysics ( § 11). Finally, from the theoretical side, McKernan et al (2021) and McKernan et al (in prep. ) discuss how stars embedded in AGN accretion disks can lead to TDEs.…”

Section: Active Galactic Nucleimentioning

confidence: 94%

Science with the Ultraviolet Explorer (UVEX)

Kulkarni¹,

Harrison²,

Grefenstette³

et al. 2021

Preprint

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The Ultraviolet Explorer (UVEX ) will undertake a synoptic survey of the entire sky in near-UV (NUV) and far-UV (FUV) bands, probing the dynamic FUV and NUV universe, as well as perform a modern, all-sky imaging survey that reaches ≥ 50 times deeper than GALEX . Combined with a powerful broadband spectroscopic capability and timely response to target of opportunity discoveries, UVEX will address fundamental questions from the NASA Astrophysics Roadmap and the Astro2020 Decadal Survey, enabling unique and important studies across the breadth of astrophysics. Imaging and spectroscopic surveys with UVEX will probe key aspects of the evolution of galaxies by understanding how star formation and stellar evolution at low metallicities affect the growth and evolution of lowmetallicity, low-mass galaxies in the local universe. Such galaxies contain half the mass in the local universe, and are analogs for the first galaxies, but observed at distances that make them accessible to detailed study. The UVEX time-domain surveys and prompt spectroscopic follow-up capability will probe the environments, energetics, and emission processes in the early aftermaths of gravitational wave-discovered compact object mergers, discover hot, fast UV transients, and diagnose the early stages of explosive phenomena. UVEX will become a key community resource by filling a gap in the new generation of wide-field, sensitive optical and infrared surveys provided by the Rubin, Euclid , and Roman observatories. We discuss the scientific potential of UVEX , including unique studies UVEX will enable for studying exoplanet atmospheres, hot stars, explosive phenomena, black holes, and galaxy evolution.

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“…The resulting TDE is super-luminous, since none of the stellar ejecta escapes; rather it collides with AGN disk gas at small disk radii and drives a high accretion rate event. These events should be more luminous than TDEs in quiescent galactic nuclei and have shorter characteristic timescales (McKernan et al 2021).…”

Section: Immortal Star + Smbhmentioning

confidence: 98%

“…There is an AGN loss-cone which results from the scatterings of stars and other objects onto the SMBH (e.g. McKernan et al 2021). If an immortal star is scattered onto, or close enough to, the SMBH, a tidal disruption event (TDE) can occur.…”

Section: Immortal Star + Smbhmentioning

confidence: 99%

Effects of an Immortal Stellar Population in AGN Disks

Jermyn,

Dittmann,

McKernan

et al. 2022

Preprint

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Stars are likely embedded in the gas disks of Active Galactic Nuclei (AGN). Theoretical models predict that in the inner regions of the disk these stars accrete rapidly, with fresh gas replenishing hydrogen in their cores faster than it is burned into helium, effectively stalling their evolution at hydrogen burning. We produce order-of-magnitude estimates of the number of such stars in a fiducial AGN disk. We find numbers of order 10 2−4 , confined to the inner r cap ∼ 3000r s ∼ 0.03pc. These stars can profoundly alter the chemistry of AGN disks, enriching them in helium and depleting them in hydrogen, both by order-unity amounts. We further consider mergers between these stars and other disk objects, suggesting that star-star mergers result in rapid mass loss from the remnant to restore an equilibrium mass, while star-compact object mergers may result in exotic outcomes and even host binary black hole mergers within themselves. Finally, we examine how these stars react as the disk dissipates towards the end of its life, and find that they may return mass to the disk fast enough to extend its lifetime by a factor of several and/or may drive powerful outflows from the disk. Post-AGN, these stars rapidly lose mass and form a population of stellar mass black holes around 10M . Due to the complex and uncertain interactions between embedded stars and the disk, their plausible ubiquity, and their order unity impact on disk structure and evolution, they must be included in realistic disk models.

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Starfall: A heavy rain of stars in 'turning on' AGN

Cited by 6 publications

References 46 publications

An Analytic, Fully Relativistic Framework for Tidal Disruption Event Streams in Schwarzschild Geometry

An Analytic, Fully Relativistic Framework for Tidal Disruption Event Streams in Schwarzschild Geometry

Science with the Ultraviolet Explorer (UVEX)

Effects of an Immortal Stellar Population in AGN Disks

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