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EMRI + TDE = QPE: Periodic X-ray Flares from Star-Disk Collisions in Galactic Nuclei
High Energy Astrophysical Phenomena · Submitted 28 Mar 2023
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim We show that a main-sequence star (brought into the nucleus as an extreme mass-ratio inspiral; EMRI) which passes twice per orbit through the accretion disk of the supermassive black-hole (SMBH) on a mildly eccentric inclined orbit, each time shocking and ejecting optically-thick gas clouds above and below the midplane, naturally reproduces observed properties of QPE flares.
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The abstract, sentence by sentence
Roughly half of the quasi-periodic eruption (QPE) sources in galactic nuclei exhibit a remarkably regular alternating "long-short'' pattern of recurrence times between consecutive flares. We show that a main-sequence star (brought into the nucleus as an extreme mass-ratio inspiral; EMRI) which passes twice per orbit through the accretion disk of the supermassive black-hole (SMBH) on a mildly eccentric inclined orbit, each time shocking and ejecting optically-thick gas clouds above and below the midplane, naturally reproduces observed properties of QPE flares. Inefficient photon production in the ejecta renders the QPE emission much harder than the blackbody temperature, enabling the flares to stick out from the softer quiescent disk spectrum. Destruction of the star via mass ablation limits the QPE lifetime to decades, precluding a long-lived AGN as the gaseous disk. By contrast, a tidal disruption event (TDE) naturally provides a transient gaseous disk on the requisite radial scale, with a rate exceeding the EMRI inward migration rate, suggesting that many TDEs should host a QPE. This picture is consistent with the X-ray TDE observed several years prior to the QPE appearance from GSN 069. Remarkably, a second TDE-like flare was observed from this event, starting immediately after detectable QPE activity ceased; this event could plausibly result from the (partial or complete) destruction of the QPE-generating star triggered by runaway mass-loss, though other explanations cannot be excluded. Our model can also be applied to black hole-disk collisions, such as those invoked in the context of the candidate SMBH binary OJ 287.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Roughly half of the quasi-periodic eruption (QPE) sources in galactic nuclei exhibit a remarkably regular alternating "long-short'' pattern of recurrence times between consecutive flares. | background 0.86 | 0.23 | 0.07 | asserted 0.98 |
| s1 | We show that a main-sequence star (brought into the nucleus as an extreme mass-ratio inspiral; EMRI) which passes twice per orbit through the accretion disk of the supermassive black-hole (SMBH) on a mildly eccentric inclined orbit, each time shocking and ejecting optically-thick gas clouds above and below the midplane, naturally reproduces observed properties of QPE flares. | contribution 0.76 | 0.85 | 0.79 | asserted 1.00 |
| s2 | Inefficient photon production in the ejecta renders the QPE emission much harder than the blackbody temperature, enabling the flares to stick out from the softer quiescent disk spectrum. | interpretation 0.50 | 0.64 | 0.05 | asserted 1.00 |
| s3 | Destruction of the star via mass ablation limits the QPE lifetime to decades, precluding a long-lived AGN as the gaseous disk. | result 0.65 | 0.67 | 0.08 | asserted 1.00 |
| s4 | By contrast, a tidal disruption event (TDE) naturally provides a transient gaseous disk on the requisite radial scale, with a rate exceeding the EMRI inward migration rate, suggesting that many TDEs should host a QPE. | interpretation 0.68 | 0.48 | 0.19 | hedged possibility 0.92 |
| s5 | This picture is consistent with the X-ray TDE observed several years prior to the QPE appearance from GSN 069. | interpretation 0.73 | 0.16 | 0.05 | hedged possibility 0.96 |
| s6 | Remarkably, a second TDE-like flare was observed from this event, starting immediately after detectable QPE activity ceased; this event could plausibly result from the (partial or complete) destruction of the QPE-generating star triggered by runaway mass-loss, though other explanations cannot be excluded. | interpretation 0.92 | 0.21 | 0.05 | hedged possibility 0.99 |
| s7 | Our model can also be applied to black hole-disk collisions, such as those invoked in the context of the candidate SMBH binary OJ 287. | interpretation 0.53 | 0.40 | 0.04 | asserted 0.49 |
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The paper
Original abstract
Roughly half of the quasi-periodic eruption (QPE) sources in galactic nuclei exhibit a remarkably regular alternating "long-short'' pattern of recurrence times between consecutive flares. We show that a main-sequence star (brought into the nucleus as an extreme mass-ratio inspiral; EMRI) which passes twice per orbit through the accretion disk of the supermassive black-hole (SMBH) on a mildly eccentric inclined orbit, each time shocking and ejecting optically-thick gas clouds above and below the midplane, naturally reproduces observed properties of QPE flares. Inefficient photon production in the ejecta renders the QPE emission much harder than the blackbody temperature, enabling the flares to stick out from the softer quiescent disk spectrum. Destruction of the star via mass ablation limits the QPE lifetime to decades, precluding a long-lived AGN as the gaseous disk. By contrast, a tidal disruption event (TDE) naturally provides a transient gaseous disk on the requisite radial scale, with a rate exceeding the EMRI inward migration rate, suggesting that many TDEs should host a QPE. This picture is consistent with the X-ray TDE observed several years prior to the QPE appearance from GSN 069. Remarkably, a second TDE-like flare was observed from this event, starting immediately after detectable QPE activity ceased; this event could plausibly result from the (partial or complete) destruction of the QPE-generating star triggered by runaway mass-loss, though other explanations cannot be excluded. Our model can also be applied to black hole-disk collisions, such as those invoked in the context of the candidate SMBH binary OJ 287.
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References
How the literature uses it
29 arXiv papers cite this in 75 sentences
Papers citing it · 54 sentences without a confident label
Contests it 1 paper
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Meanwhile, in [ref] , the luminosity may be overestimated since the photon diffusion velocity is slower than the expansion velocity of shocked gas in their fiducial model, which needs to be considered as in [ref] .
Flares from stars crossing active galactic nuclei disks on low-inclination orbits · Conclusions · contest 0.73
Compares with it 3 papers
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Nevertheless, our conclusions are similar to those of [ref] and [ref] , namely that collisions between a star and an AGN disk offers a viable explanation for observed QPE flares.
Flares from stars crossing active galactic nuclei disks on low-inclination orbits · Conclusions · 0.94
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We note that the star-disc interaction described in [ref] involves a low-mass, compact accretion disc which originated from a second star undergoing a TDE in the same galactic nucleus, such that star-disc collisions only commence once the EMRI is on few-hour period, as opposed to the case of an extended AGN disc.
Period Evolution of Repeating Transients in Galactic Nuclei · Formation channel for PNTs · 0.81
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In comparison with [ref] , who study star-disk collisions, [ref] prefer secondary black holes of $∼100 M_⊙$ crossing the disk.
X-ray eruptions every 22 days from the nucleus of a nearby galaxy · Accretion disc – perturber interaction · 0.97
Cites it as background 14 papers
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The nature of the QPEs is still unclear, and its period $∼$ 9 hrs may correspond to the orbital period of a body orbiting the SMBH, but the radiative processes and the nature of the body are controversial [ref] .
Tidal disruption event associated with the quasi-periodic eruptions from GSN 069: Possible disruption of a common envelope · Introduction · 0.96
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While many models have been proposed for QPEs [ref] , only a few account for an important clue: a regular alternating behavior, observed in at least two of the QPE sources$-$GSN 069 [ref] and eRO-QPE2 [ref] , in which the temporal spacing between consecutive eruptions varies back and forth by around 10%.
Coupled Disk-Star Evolution in Galactic Nuclei and the Lifetimes of QPE Sources · Introduction · 0.95
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Many models have been proposed for explaining the physical origin of QPEs, based on different disk instabilities[The classical limit-cycle instability in AGN disks is disfavored because the the QPE periods, burst timescales and burst profiles cannot be reconciled with the limit-cycle prediction [ref] . ] [ref] , self-lensing binary massive black hole [ref] , mass transfer at pericenter from stars or white dwarfs orbiting around the SMBH [ref] , (periodic) impacts between a stellar-mass object (SMO), a star or a stellar mass black hole (sBH), and the accretion disk that is formed following a recent TDE (dubbed as EMRI+TDE disk model) [ref] .
Probing orbits of stellar mass objects deep in galactic nuclei with quasi-periodic eruptions · Introduction · 0.83
What it cites · 25 sentences without a confident label
Contests 1 paper
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* Although aspects of our model resemble those which attribute QPE X-ray emission to shocks associated with the circularization of tidally stripped matter from a stellar EMRI on a mildly eccentric orbit [ref] , this class of models are in tension with the observed long-short oscillations, which are more easily explained with two flares occurring per orbital period.
Quasi-periodic eruptions from mildly eccentric unstable mass transfer in galactic nuclei · Discussion and Conclusions · contest 0.77
Cites as support 1 paper
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* Since two collisions occur per orbit, and (half of) the debris is visible from both sides of the disk (i.e., for most observer viewing angles), a moderately eccentric orbit naturally gives rise to alternating long-short recurrence interval between QPE flares [ref] .
Quasi-periodic eruptions from impacts between the secondary and a rigidly precessing accretion disc in an extreme mass-ratio inspiral system · Discussion and Conclusions · 0.98
Cites as background 6 papers
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Several theoretical models have been proposed to explain the QPE phenomenon, including (i) accretion disc instabilities [ref] ; (ii) gravitational lensing of a SMBH binary [ref] ; (iii) mass transfer onto a SMBH from one or more orbiting bodies [ref] ; and (iv) collisions between an orbiting secondary body and the SMBH accretion disk [ref] .
Modified models of radiation pressure instability in application to 10, 10$^5$, and 10$^7$ $M_{\odot}$ accreting black holes · Introduction · 0.99
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Several theoretical models have been proposed to explain the QPE phenomenon, including (i) accretion disc instabilities [ref] ; (ii) gravitational lensing of a SMBH binary [ref] ; (iii) mass transfer onto a SMBH from one or more orbiting bodies [ref] ; and (iv) collisions between an orbiting secondary body and the SMBH accretion disk [ref] .
Quasi-periodic eruptions from mildly eccentric unstable mass transfer in galactic nuclei · Introduction · 0.99
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Several theoretical models have been proposed to explain the QPE phenomenon, including (i) accretion disc instabilities [ref] ; (ii) gravitational lensing of a SMBH binary [ref] ; (iii) mass transfer onto a SMBH from one or more orbiting bodies [ref] ; and (iv) collisions between an orbiting secondary body and the SMBH accretion disk [ref] .
Tidal Stripping of a White Dwarf by an Intermediate-Mass Black Hole · Introduction · 0.99
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