Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

An energetic hot wind from the low-luminosity active galactic nucleus M81*


For most of their lifetime, super-massive black holes (SMBHs) commonly found in galactic nuclei obtain mass from the ambient medium at a rate well below the Eddington limit1, which is mediated by a radiatively inefficient, hot accretion flow2. Both theory and numerical simulations predict that a strong wind must exist in such hot accretion flows3,4,5,6. The wind is of special interest not only because it is an indispensable ingredient of accretion but also, perhaps more importantly, because it is believed to play a crucial role in the evolution of the host galaxy via the so-called kinetic mode active galactic nucleus feedback7,8. Observational evidence for this wind, however, remains scarce and indirect9,10,11,12. Here we report the detection of a hot outflow from the low-luminosity active galactic nucleus in M81, based on Chandra high-resolution X-ray spectroscopy. The outflow is evidenced by a pair of Fe xxvi Lyα lines redshifted and blueshifted at a bulk line-of-sight velocity of ±2.8 × 103 km s−1 and a high line ratio of Fe xxvi Lyα to Fe xxv Kα implying a plasma temperature of 1.3 × 108 K. This high-velocity, hot plasma cannot be produced by stellar activity or the accretion inflow onto the SMBH. Our magnetohydrodynamical simulations show that, instead, it is naturally explained by a wind from the hot accretion flow, propagating out to 106 times the gravitational radius of the SMBH. The kinetic energy and momentum of this wind can significantly affect the evolution of the circumnuclear environment and beyond.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Prices vary by article type



Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Detection and characterization of highly ionized Fe lines.
Fig. 2: The hot wind model.

Data availability

Source data are provided with this paper. The original X-ray data used in this work are publicly available in the online HEASARC archive at Reduced X-ray spectra are available in Supplementary Data 15.

Code availability

Spectral analysis is conducted using Xspec (https://heasarc.gsfc.nasa. gov/docs/xanadu/xspec/), which employs ATOMDB for the modelling of atomic lines. The ZEUS-MP/2 and ATHENA++ codes used in this work are publicly available at and at The wind simulation data for Fig. 2 are provided with this paper.


  1. Ho, L. C. Nuclear activity in nearby galaxies. Annu. Rev. Astron. Astrophys. 46, 475–539 (2008).

    Article  ADS  Google Scholar 

  2. Yuan, F. & Narayan, R. Hot accretion flows around black holes. Annu. Rev. Astron. Astrophys. 52, 529–588 (2014).

    Article  ADS  Google Scholar 

  3. Blandford, R. D. & Begelman, M. C. On the fate of gas accreting at a low rate on to a black hole. Mon. Not. R. Astron. Soc. 303, L1–L5 (1999).

    Article  ADS  Google Scholar 

  4. Yuan, F., Bu, D. & Wu, M. Numerical simulation of hot accretion flows. II. Nature, origin, and properties of outflows and their possible observational applications. Astrophys. J. 761, 130 (2012).

    Article  ADS  Google Scholar 

  5. Narayan, R., Sądowski, A., Penna, R. F. & Kulkarni, A. K. GRMHD simulations of magnetized advection-dominated accretion on a non-spinning black hole: role of outflows. Mon. Not. R. Astron. Soc. 426, 3241–3259 (2012).

    Article  ADS  Google Scholar 

  6. Yuan, F. et al. Numerical simulation of hot accretion flows. III. Revisiting wind properties using the trajectory approach. Astrophys. J. 804, 101 (2015).

    Article  ADS  Google Scholar 

  7. Weinberger, R. et al. Simulating galaxy formation with black hole driven thermal and kinetic feedback. Mon. Not. R. Astron. Soc. 465, 3291–3308 (2017).

    Article  ADS  Google Scholar 

  8. Yoon, D., Yuan, F., Ostriker, J. P., Ciotti, L. & Zhu, B. On the role of the hot feedback mode in active galactic nuclei feedback in an elliptical galaxy. Astrophys. J. 885, 16 (2019).

    Article  ADS  Google Scholar 

  9. Wang, Q. D. et al. Dissecting X-ray-emitting gas around the center of our Galaxy. Science 341, 981–983 (2013).

    Article  ADS  Google Scholar 

  10. Cheung, E. et al. Suppressing star formation in quiescent galaxies with supermassive black hole winds. Nature 533, 504–508 (2016).

    Article  ADS  Google Scholar 

  11. Tombesi, F. et al. Ultrafast outflows in radio-loud active galactic nuclei. Mon. Not. R. Astron. Soc. 443, 2154–2182 (2014).

    Article  ADS  Google Scholar 

  12. Peng, S. et al. Resolving the nuclear radio emission from M32 with the Very Large Array. Astrophys. J. 894, 61 (2020).

    Article  ADS  Google Scholar 

  13. Freedman, W. L. et al. The Hubble Space Telescope Extragalactic Distance Scale Key Project. I. The discovery of Cepheids and a new distance to M81. Astrophys. J. 427, 628–655 (1994).

    Article  ADS  Google Scholar 

  14. Devereux, N., Ford, H., Tsvetanov, Z. & Jacoby, G. STIS spectroscopy of the central 10 parsecs of M81: evidence for a massive black hole. Astron. J. 125, 1226–1235 (2003).

    Article  ADS  Google Scholar 

  15. Nemmen, R. S., Storchi-Bergmann, T. & Eracleous, M. Spectral models for low-luminosity active galactic nuclei in LINERs: the role of advection-dominated accretion and jets. Mon. Not. R. Astron. Soc. 438, 2804–2827 (2014).

    Article  ADS  Google Scholar 

  16. Bietenholz, M. F., Bartel, N. & Rupen, M. P. A stationary core with a one-sided jet in the center of M81. Astrophys. J. 532, 895–908 (2000).

    Article  ADS  Google Scholar 

  17. Ho, L. C., Filippenko, A. V. & Sargent, W. L. W. New insights into the physical nature of LINERs from a multiwavelength analysis of the nucleus of M81. Astrophys. J. 462, 183–202 (1996).

    Article  ADS  Google Scholar 

  18. Young, A. J., McHardy, I., Emmanoulopoulos, D. & Connolly, S. The absence of a thin disc in M81*. Mon. Not. R. Astron. Soc. 476, 5698–5703 (2018).

    Article  ADS  Google Scholar 

  19. Dewangan, G. C., Griffiths, R. E., Di Matteo, T. & Schurch, N. J. Iron Kα emission from the low-luminosity active galaxies M81 and NGC 4579. Astrophys. J. 607, 788–793 (2004).

    Article  ADS  Google Scholar 

  20. Page, M. J., Soria, R., Zane, S., Wu, K. & Starling, R. L. C. Highly ionized Fe Kα emission lines from the LINER galaxy M 81. Astron. Astrophys. 422, 77–84 (2004).

    Article  ADS  Google Scholar 

  21. Young, A. J., Nowak, M. A., Markoff, S., Marshall, H. L. & Canizares, C. R. High-resolution X-ray spectroscopy of a low-luminosity active galactic nucleus: the structure and dynamics of M81*. Astrophys. J. 669, 830–840 (2007).

    Article  ADS  Google Scholar 

  22. Palmeri, P., Mendoza, C., Kallman, T. R., Bautista, M. A. & Meléndez, M. Modeling of iron K lines: radiative and Auger decay data for Fe ii–Fe ix. Astron. Astrophys. 410, 359–364 (2003).

    Article  ADS  Google Scholar 

  23. Smith, R. K., Brickhouse, N. S., Liedahl, D. A. & Raymond, J. C. Collisional plasma models with APEC/APED: emission-line diagnostics of hydrogen-like and helium-like ions. Astrophys. J. 556, L91–L95 (2001).

    Article  ADS  Google Scholar 

  24. Dwarkadas, V. V. & Gruszko, J. What are published X-ray light curves telling us about young supernova expansion? Mon. Not. R. Astron. Soc. 419, 1515–1524 (2012).

    Article  ADS  Google Scholar 

  25. Schmidt, B. P. et al. The unusual supernova SN1993J in the galaxy M81. Nature 364, 600–602 (1993).

    Article  ADS  Google Scholar 

  26. Gagné, M. et al. An X-ray survey of colliding wind binaries. ASP Conf. Ser. 465, 301 (2012).

    ADS  Google Scholar 

  27. Guo, F., Duan, X. & Yuan, Y.-F. Reversing cooling flows with AGN jets: shock waves, rarefaction waves and trailing outflows. Mon. Not. R. Astron. Soc. 473, 1332–1345 (2018).

    Article  ADS  Google Scholar 

  28. King, A. L. et al. Discrete knot ejection from the jet in a nearby low-luminosity active galactic nucleus, M81*. Nat. Phys. 12, 772–777 (2016).

    Article  Google Scholar 

  29. Schnorr Müller, A. et al. Gas streaming motions towards the nucleus of M81. Mon. Not. R. Astron. Soc. 413, 149–161 (2011).

    Article  ADS  Google Scholar 

  30. Ricci, T. V., Steiner, J. E. & Giansante, L. A hot bubble at the centre of M 81. Astron. Astrophys. 576, A58 (2015).

    Article  ADS  Google Scholar 

  31. Sell, P. H. et al. Luminosity functions and point-source properties from multiple Chandra observations of M81. Astrophys. J. 735, 26 (2011).

    Article  ADS  Google Scholar 

  32. Cash, W. Parameter estimation in astronomy through application of the likelihood ratio. Astrophys. J. 228, 939–947 (1979).

    Article  ADS  Google Scholar 

  33. Kalberla, P. M. W. et al. The Leiden/Argentine/Bonn (LAB) Survey of Galactic H i. Final data release of the combined LDS and IAR surveys with improved stray-radiation corrections. Astron. Astrophys. 440, 775–782 (2005).

    Article  ADS  Google Scholar 

  34. La Parola, V. et al. Long-term X-ray spectral variability of the nucleus of M81. Astrophys. J. 601, 831–844 (2004).

    Article  ADS  Google Scholar 

  35. Miller, J. M., Nowak, M., Markoff, S., Rupen, M. P. & Maitra, D. Exploring accretion and disk–jet connections in the LLAGN M81*. Astrophys. J. 720, 1033–1037 (2010).

    Article  ADS  Google Scholar 

  36. Tombesi, F. et al. Evidence for ultra-fast outflows in radio-quiet AGNs. I. Detection and statistical incidence of Fe K-shell absorption lines. Astron. Astrophys. 521, A57 (2010).

    Article  Google Scholar 

  37. Bower, G. A. et al. The stellar dynamics in the centers of the LINER galaxies M81 and NGC 3998. Bull. Am. Astron. Soc. 32, 1566 (2000).

    ADS  Google Scholar 

  38. Kormendy, J. & Ho, L. C. Coevolution (or not) of supermassive black holes and host galaxies. Annu. Rev. Astron. Astrophys. 51, 511–653 (2013).

    Article  ADS  Google Scholar 

  39. Mannucci, F. et al. The supernova rate per unit mass. Astron. Astrophys. 433, 807–814 (2005).

    Article  ADS  Google Scholar 

  40. Kennicutt, R. C.Jr Star formation in galaxies along the Hubble sequence. Annu. Rev. Astron. Astrophys. 36, 189–232 (1998).

    Article  ADS  Google Scholar 

  41. Rimoldi, A., Rossi, E. M., Costantini, E. & Portegies Zwart, S. The contribution of young core-collapse supernova remnants to the X-ray emission near quiescent supermassive black holes. Mon. Not. R. Astron. Soc. 456, 2537–2549 (2016).

    Article  ADS  Google Scholar 

  42. Lehmer, B. D. et al. A Chandra perspective on galaxy-wide X-ray binary emission and its correlation with star formation rate and stellar mass: new results from luminous infrared galaxies. Astrophys. J. 724, 559–571 (2010).

    Article  ADS  Google Scholar 

  43. Ranalli, P., Comastri, A. & Setti, G. The 2–10 keV luminosity as a Star Formation Rate indicator. Astron. Astrophys. 399, 39–50 (2003).

    Article  ADS  Google Scholar 

  44. Ferland, G. J. et al. The 2017 release of Cloudy. Rev. Mex. Astron. Astrofis. 53, 385–438 (2017).

    ADS  Google Scholar 

  45. Bianchi, S. & Matt, G. Ionized iron Kα lines in AGN X-ray spectra. Astron. Astrophys. 387, 76–81 (2002).

    Article  ADS  Google Scholar 

  46. White, C. J., Stone, J. M. & Gammie, C. F. An extension of the Athena++ code framework for GRMHD based on advanced Riemann solvers and staggered-mesh constrained transport. Astrophys. J. Suppl. Ser. 225, 22 (2016).

    Article  ADS  Google Scholar 

  47. Yang, H., Yuan, F., Yuan, Y.-F., White, C. J. Numerical simulation of hot accretion flow (IV): effects of black hole spin and magnetic field strength on the wind and the comparison between wind and jet properties. Preprint at (2021).

Download references


This research made use of observations taken at the Chandra X-ray Observatory, the software package CIAO provided by the Chandra X-ray Center, the spectral fitting package Xspec, and the High Performance Computing Resource at the Core Facility for Advanced Research Computing at the Shanghai Astronomical Observatory. Z.L. and F.S. acknowledges support by the National Key Research and Development Program of China (grant no. 2017YFA0402703) and Natural Science Foundation of China (grant no. 11873028). F.Y. and B.Z. are supported in part by the National Key Research and Development Program of China (grant no. 2016YFA0400704), the Natural Science Foundation of China (grant no. 11633006) and the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences (grant no. QYZDJSSW-SYS008). We thank C. Cui and H. Yang for help with initial model tests and GRMHD simulation of hot accretion flows, and J. Wang for helpful discussions.

Author information

Authors and Affiliations



This research programme was designed and framed by Z.L. and F.Y. Analysis and modelling of the X-ray data were performed by F.S. with the help of Z.L. Numerical simulations of the accretion flow and wind were performed by B.Z. and F.Y. All authors were involved in the discussion and interpretation of the results presented, and all contributed to writing the paper.

Corresponding authors

Correspondence to Zhiyuan Li or Feng Yuan.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature Astronomy thanks Andrew Young and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 The combined Chandra/HETG images highlighting the 1st-order MEG/HEG arms.

Spectra are extracted from the individual observations of different roll angles and then combined to form the final spectrum. The green rectangles illustrate the spectral extraction region (solid rectangles for the source and the adjacent dashed rectangles for the background) for one of the 15 observations. The NuSTAR source region is marked by the vermillion solid circle, while the corresponding background region is marked by the vermillion dashed annulus. Discrete sources falling within the NuSTAR spectral extraction regions are not excluded, but their collective flux contribution is negligible.

Extended Data Fig. 2 Observed X-ray spectra of M81*.

Red: coadded Chandra/MEG 1st-order spectrum; Black: coadded Chandra/HEG 1st-order spectrum; Green: NuSTAR/FPMA spectrum; Blue: NuSTAR/FPMB spectrum. The error bars are of 1σ. The best-fit absorbed power-law model is shown by the solid lines. The ratio of residual/error is shown in the bottom panel. Significant excess is seen between 6–7 keV due to the presence of Fe lines. The spectra shown here are binned to achieve a S/N greater than 3 for better illustration, while in the actual spectral fit throughout this work the spectra are binned to have at least one count per bin to optimize the spectral resolution.

Extended Data Fig. 3 Blind line search of the MEG and HEG spectra over 1–3 keV.

Blue, green and orange contours indicate confidence level of 99%, 90% and 68%, respectively, of a test line according to the differential C-stat value against the baseline continuum model. The black contour denotes where ΔC = + 0.5. Significant lines with an identified atomic transition are denoted with the pink vertical dashed lines.

Extended Data Fig. 4 Coadded HETG zeroth-order spectrum from an annulus of inner-to-outer radii of 2.5 –5.0 around M81*.

The spectrum can be well fitted by an absorbed power-law, shown as the magenta line. The error bars are of 1σ. The ratio of residual/error is shown in the bottom panel. An additional thermal component, represent by an apec model with a plasma temperature of 0.9 keV, is allowed by the data and shown as the blue line. The sum of the power-law and apec is plotted as the black line.

Extended Data Fig. 5 Predicted Fe line luminosity of an isotropic and uniform gas cloud photonionized by a central AGN.

The upper (lower) panel is for Fe XXVI Lyα (XXV Kα). The ionization parameter is evaluated for an intrinsic X-ray spectrum same as M81* and over photon energy of 2–10 keV. The cloud has an equivalent hydrogen column density of NH = 1023cm−2 (black solid line), 1022cm−2 (red dash-dotted line) and 1021cm−2 (blue dashed line). The black dotted horizontal line in each panel marks the observed line luminosity, which is substantially higher than the predicted values.

Extended Data Fig. 6 Predicted 6.5–7.3 keV spectrum from simulation of the hot accretion flow.

The viewing angle is set to be 45 with respect to the jet axis. The blue, red and black curves show the blueshifted, redshifted and total spectrum, respectively. The spectra have been convolved with the HEG instrumental response. The black crosses mark the observed spectrum as a reference. The error bars are of 1σ. The observed Fe XXVI and XXV lines have an equivalent width substantially higher than predicted by the hot accretion flow.

Extended Data Table 1 Log of X-ray observations
Extended Data Table 2 Additional Emission lines in the HETG spectrum

Supplementary information

Supplementary Data 1

The stacked Chandra HEG source and background spectra with the instrumental response files.

Supplementary Data 2

The stacked Chandra MEG source and background spectra with the instrumental response files.

Supplementary Data 3

The NuSTAR FPMA source and background spectra with instrumental response files.

Supplementary Data 4

The NuSTAR FPMB source and background spectra with instrumental response files.

Supplementary Data 5

The stacked Chandra HETG zero-order spectrum of an off-nuclear region with instrumental response files.

Source data

Source Data Fig. 2

Source data for the simulation results that can reproduce Fig. 2.

Rights and permissions

Reprints and Permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Shi, F., Li, Z., Yuan, F. et al. An energetic hot wind from the low-luminosity active galactic nucleus M81*. Nat Astron 5, 928–935 (2021).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing