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Nature | Letter

日本語要約

Flows of X-ray gas reveal the disruption of a star by a massive black hole

Journal name:
Nature
Volume:
526,
Pages:
542–545
Date published:
DOI:
doi:10.1038/nature15708
Received
Accepted
Published online

Tidal forces close to massive black holes can violently disrupt stars that make a close approach. These extreme events are discovered via bright X-ray1, 2, 3, 4 and optical/ultraviolet5, 6 flares in galactic centres. Prior studies based on modelling decaying flux trends have been able to estimate broad properties, such as the mass accretion rate6, 7. Here we report the detection of flows of hot, ionized gas in high-resolution X-ray spectra of a nearby tidal disruption event, ASASSN-14li in the galaxy PGC 043234. Variability within the absorption-dominated spectra indicates that the gas is relatively close to the black hole. Narrow linewidths indicate that the gas does not stretch over a large range of radii, giving a low volume filling factor. Modest outflow speeds of a few hundred kilometres per second are observed; these are below the escape speed from the radius set by variability. The gas flow is consistent with a rotating wind from the inner, super-Eddington region of a nascent accretion disk, or with a filament of disrupted stellar gas near to the apocentre of an elliptical orbit. Flows of this sort are predicted by fundamental analytical theory8 and more recent numerical simulations7, 9, 10, 11, 12, 13, 14.

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  1. The multi-wavelength light curves of ASASSN-14li clearly signal a tidal disruption event.
    Figure 1: The multi-wavelength light curves of ASASSN-14li clearly signal a tidal disruption event.

    The light curves are based on monitoring observations with the Swift satellite. The errors shown on plotting symbols are the 1σ confidence limits on the flux in each band (V, B, U, UVW1 (here W1), UVM2 (M2), UVW2 (W2). Contributions from the host galaxy have been subtracted (see Methods). The UVM2 filter samples the ultraviolet light especially well. The grey shading depicts the t−5/3 flux decay predicted by fundamental theory8, 19. The X-ray flux points carry relatively large errors; a representative error bar is shown at right. Fits to the decay curve are described in the main text and in the Methods.

  2. The high-resolution X-ray spectra of ASASSN-14li reveal blueshifted absorption lines.
    Figure 2: The high-resolution X-ray spectra of ASASSN-14li reveal blueshifted absorption lines.

    Spectra from the ‘long stare’ with XMM-Newton and the combined Chandra spectrum are shown. XMM-Newton spectra from the RGS1 and RGS2 units are shown in black and blue, respectively; the RGS2 unit is missing a detector in the 20–24 Å band. The best-fit photoionized absorption model for the outflowing gas detected in each spectrum is shown in red (see Methods), and selected strong lines are indicated. Below each spectrum, the goodness-of-fit statistic (Δχ2) is shown before (cyan) and after (black) modelling the absorbing gas. The errors on the spectra are 1σ confidence limits on the flux in each bin.

  3. The temperature of the blackbody continuum emission from ASASSN-14li is steady over time.
    Figure 3: The temperature of the blackbody continuum emission from ASASSN-14li is steady over time.

    The temperature measured in simple blackbody fits to Swift/XRT monitoring observations is plotted versus time. Errors are 1σ confidence intervals. The temperature is remarkably steady, contrasting strongly with the declining fluxes shown in Fig. 1. Recent theory suggests that winds may serve to maintain steady temperatures in some TDEs14.

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Author information

Affiliations

  1. Department of Astronomy, The University of Michigan, 1085 South University Avenue, Ann Arbor, Michigan 48103, USA

    • Jon M. Miller,
    • Mark T. Reynolds &
    • Kayhan Gultekin

  2. SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands

    • Jelle S. Kaastra &
    • Jelle de Plaa

  3. Department of Physics and Astronomy, Universiteit Utrecht, PO Box 80000, 3508 TA Utrecht, The Netherlands

    • Jelle S. Kaastra

  4. Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

    • Jelle S. Kaastra

  5. Department of Astronomy, The University of Maryland, College Park, Maryland 20742, USA

    • M. Coleman Miller,
    • Suvi Gezari &
    • Richard Mushotzky

  6. Department of Physics, University of Warwick, Coventry CV4 7AL, UK

    • Gregory Brown &
    • Andrew Levan

  7. Joint Space-Science Institute, University of Maryland, College Park, Maryland 02742, USA

    • S. Bradley Cenko &
    • Tod Strohmayer

  8. Astrophysics Science Division, NASA Goddard Space Flight Center, MC 661, Greenbelt, Maryland 20771, USA

    • S. Bradley Cenko

  9. Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, Massachusetts 02138, USA

    • Jeremy J. Drake

  10. The Institute for Theory and Computation, Harvard–Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA

    • James Guillochon

  11. Department of Physics and Astronomy, University of Alabama, PO Box 870324, Tuscaloosa, Alabama 35487, USA

    • Jimmy Irwin &
    • W. Peter Maksym

  12. Department of Physics and Astronomy, Wheaton College, Norton, Massachusetts 02766, USA

    • Dipankar Maitra

  13. Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK

    • Paul O’Brien &
    • Nial Tanvir

  14. Columbia Astrophysics Laboratory and Department of Astronomy, Columbia University, 550 West 120th Street, New York, New York 10027, USA

    • Frits Paerels

  15. Department of Astronomy and Astrophysics, University of California, Santa Cruz, California 95064, USA

    • Enrico Ramirez-Ruiz

Contributions

J.M.M. led the Chandra and XMM-Newton data reduction and analysis, with contributions from J.S.K., J.J.D. and J.d.P. M.T.R. led the Swift data reduction and analysis (with help from S.B.C., S.G. and R.M.). M.C.M., E.R.-R. and J.G. provided theoretical insights. G.B., K.G., J.I., A.L., D.M., W.P.M., P.O’B., F.P., T.S. and N.T. contributed to the discussion and interpretation.

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The authors declare no competing financial interests.

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