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.

You are viewing this page in draft mode.

The quiescent intracluster medium in the core of the Perseus cluster


Clusters of galaxies are the most massive gravitationally bound objects in the Universe and are still forming. They are thus important probes1 of cosmological parameters and many astrophysical processes. However, knowledge of the dynamics of the pervasive hot gas, the mass of which is much larger than the combined mass of all the stars in the cluster, is lacking. Such knowledge would enable insights into the injection of mechanical energy by the central supermassive black hole and the use of hydrostatic equilibrium for determining cluster masses. X-rays from the core of the Perseus cluster are emitted by the 50-million-kelvin diffuse hot plasma filling its gravitational potential well. The active galactic nucleus of the central galaxy NGC 1275 is pumping jetted energy into the surrounding intracluster medium, creating buoyant bubbles filled with relativistic plasma. These bubbles probably induce motions in the intracluster medium and heat the inner gas, preventing runaway radiative cooling—a process known as active galactic nucleus feedback2,3,4,5,6. Here we report X-ray observations of the core of the Perseus cluster, which reveal a remarkably quiescent atmosphere in which the gas has a line-of-sight velocity dispersion of 164 ± 10 kilometres per second in the region 30–60 kiloparsecs from the central nucleus. A gradient in the line-of-sight velocity of 150 ± 70 kilometres per second is found across the 60-kiloparsec image of the cluster core. Turbulent pressure support in the gas is four per cent of the thermodynamic pressure, with large-scale shear at most doubling this estimate. We infer that a total cluster mass determined from hydrostatic equilibrium in a central region would require little correction for turbulent pressure.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Full array spectrum of the core of the Perseus cluster obtained by the Hitomi observatory.
Figure 2: Spectra of Fe xxv Heα, Fe xxvi Lyα and Fe xxv Heβ from the outer region.
Figure 3: The region of the Perseus cluster observed by the SXS.


  1. 1

    Allen, S. W., Evrard, A. E. & Mantz, A. B. Cosmological parameters from observations of galaxy clusters. Annu. Rev. Astron. Astrophys. 49, 409–470 (2011)

    ADS  Article  Google Scholar 

  2. 2

    Boehringer, H., Voges, W., Fabian, A. C., Edge, A. C. & Neumann, D. M. A ROSAT HRI study of the interaction of the X-ray-emitting gas and radio lobes of NGC 1275. Mon. Not. R. Astron. Soc. 264, L25–L28 (1993)

    ADS  Article  Google Scholar 

  3. 3

    Churazov, E., Forman, W., Jones, C. & Böhringer, H. Asymmetric, arc minute scale structures around NGC 1275. Astron. Astrophys. 356, 788–794 (2000)

    ADS  Google Scholar 

  4. 4

    McNamara, B. R. et al. Chandra X-Ray observations of the Hydra A cluster: an interaction between the radio source and the X-Ray-emitting gas. Astrophys. J. 534, L135–L138 (2000)

    ADS  CAS  Article  Google Scholar 

  5. 5

    Fabian, A. C. et al. Chandra imaging of the complex X-ray core of the Perseus cluster. Mon. Not. R. Astron. Soc. 318, L65–L68 (2000)

    ADS  Article  Google Scholar 

  6. 6

    Fabian, A. C. Observational evidence of active galactic nuclei feedback. Annu. Rev. Astron. Astrophys. 50, 455–489 (2012)

    ADS  CAS  Article  Google Scholar 

  7. 7

    Takahashi, T. et al. The ASTRO-H X-ray astronomy satellite. Proc. SPIE 9144, 914425 (2014)

    Article  Google Scholar 

  8. 8

    Mitsuda, K. et al. Soft x-ray spectrometer (SXS): the high-resolution cryogenic spectrometer onboard ASTRO-H. Proc. SPIE 9144, 91442A (2014)

    Google Scholar 

  9. 9

    Soong, Y. et al. ASTRO-H soft X-ray telescope (SXT). Proc. SPIE 9144, 914428 (2014)

    Article  Google Scholar 

  10. 10

    Tamura, T. et al. X-ray spectroscopy of the core of the Perseus cluster with Suzaku: elemental abundances in the intracluster medium. Astrophys. J. 705, L62–L66 (2009)

    ADS  CAS  Article  Google Scholar 

  11. 11

    Sanders, J. S., Fabian, A. C., Smith, R. K. & Peterson, J. R. A direct limit on the turbulent velocity of the intracluster medium in the core of Abell 1835 from XMM-Newton. Mon. Not. R. Astron. Soc. 402, L11–L15 (2010)

    ADS  Article  Google Scholar 

  12. 12

    Sanders, J. S., Fabian, A. C. & Smith, R. K. Constraints on turbulent velocity broadening for a sample of clusters, groups and elliptical galaxies using XMM-Newton. Mon. Not. R. Astron. Soc. 410, 1797–1812 (2011)

    ADS  CAS  Google Scholar 

  13. 13

    Pinto, C. et al. Chemical Enrichment RGS cluster Sample (CHEERS): constraints on turbulence. Astron. Astrophys. 575, A38 (2015)

    Article  Google Scholar 

  14. 14

    Churazov, E., Forman, W., Jones, C. & Böhringer, H. XMM-Newton observations of the Perseus cluster. I. The temperature and surface brightness structure. Astrophys. J. 590, 225–237 (2003)

    ADS  Article  Google Scholar 

  15. 15

    Churazov, E., Sunyaev, R., Gilfanov, M., Forman, W. & Jones, C. The 6.4-keV fluorescent iron line from cluster cooling flows. Mon. Not. R. Astron. Soc. 297, 1274–1278 (1998)

    ADS  CAS  Article  Google Scholar 

  16. 16

    Foster, A. R., Li, J., Smith, R. K. & Brickhouse, N. S. Updated atomic data and calculations for X-Ray spectroscopy. Astrophys. J. 756, 128 (2012)

    ADS  Article  Google Scholar 

  17. 17

    Kaastra, J. S., Mewe, R. & Nieuwenhuijzen, H. SPEX: a new code for spectral analysis of X & UV spectra. In 11th Colloquium on UV and X-ray Spectroscopy of Astrophysical and Laboratory Plasmas (eds Yamashita, K. & Watanabe, T. ) 411–414 (1996)

  18. 18

    Gil’fanov, M. R., Syunyaev, R. A. & Churazov, E. M. Radial brightness profiles of resonance x-ray lines in galaxy clusters. Sov. Astron. Lett. 13, 3–7 (1987)

    ADS  Google Scholar 

  19. 19

    Zhuravleva, I. et al. Resonant scattering in the Perseus cluster: spectral model for constraining gas motions with Astro-H. Mon. Not. R. Astron. Soc. 435, 3111–3121 (2013)

    ADS  Article  Google Scholar 

  20. 20

    Tamura, T. et al. Gas bulk motion in the Perseus cluster measured with Suzaku. Astrophys. J. 782, 38 (2014)

    ADS  Article  Google Scholar 

  21. 21

    Salomé, P. et al. A very extended molecular web around NGC 1275. Astron. Astrophys. 531, A85 (2011)

    Article  Google Scholar 

  22. 22

    Hatch, N. A., Crawford, C. S., Johnstone, R. M. & Fabian, A. C. On the origin and excitation of the extended nebula surrounding NGC 1275. Mon. Not. R. Astron. Soc. 367, 433–448 (2006)

    ADS  CAS  Article  Google Scholar 

  23. 23

    Bruggen, M., Hoeft, M. & Ruszkowski, M. X-Ray line tomography of AGN-induced motion in clusters of galaxies. Astrophys. J. 628, 153–159 (2005)

    ADS  Article  Google Scholar 

  24. 24

    Heinz, S., Bruggen, M. & Morsony, B. Prospects of high-resolution X-ray spectroscopy for active galactic nucleus feedback in galaxy clusters. Astrophys. J. 708, 462–468 (2010)

    ADS  CAS  Article  Google Scholar 

  25. 25

    Markevitch, M. & Vikhlinin, A. Shocks and cold fronts in galaxy clusters. Phys. Rep. 443, 1–53 (2007)

    ADS  Article  Google Scholar 

  26. 26

    Fabian, A. C. et al. A deep Chandra observation of the Perseus cluster: shocks and ripples. Mon. Not. R. Astron. Soc. 344, L43–L47 (2003)

    ADS  Article  Google Scholar 

  27. 27

    Ruszkowski, M., Brüggen, M. & Begelman, M. C. Cluster heating by viscous dissipation of sound waves. Astrophys. J. 611, 158–163 (2004)

    ADS  Article  Google Scholar 

  28. 28

    Zhuravleva, I. et al. Turbulent heating in galaxy clusters brightest in X-rays. Nature 515, 85–87 (2014)

    ADS  CAS  Article  Google Scholar 

  29. 29

    Gu, L. et al. Probing of the interactions between the hot plasmas and galaxies in clusters from z = 0.1 to 0.9. Astrophys. J. 767, 157 (2013)

    ADS  Article  Google Scholar 

  30. 30

    ZuHone, J. A., Markevitch, M., Brunetti, G. & Giacintucci, S. Turbulence and radio mini-halos in the sloshing cores of galaxy clusters. Astrophys. J. 762, 78 (2013)

    ADS  Article  Google Scholar 

  31. 31

    Grevesse, N. & Sauval, A. J. Standard solar composition. Space Sci. Rev. 85, 161–174 (1998)

    ADS  CAS  Article  Google Scholar 

  32. 32

    Fabian, A. C. et al. A wide Chandra view of the core of the Perseus cluster. Mon. Not. R. Astron. Soc. 418, 2154–2164 (2011)

    ADS  Article  Google Scholar 

  33. 33

    Ferruit, P., Binette, L., Sutherland, R. S. & Pencontal, E. Tiger observations of the low and high velocity components of NGC 1275. New Astron. 2, 345–363 (1997)

    ADS  Article  Google Scholar 

  34. 34

    Conselice, C., Gallagher, J. G. & Wyse, R. G. On the nature of the NGC 1275 system. Astron. J. 122, 2281–2300 (2001)

    ADS  CAS  Article  Google Scholar 

  35. 35

    Beiersdorfer, P. et al. High-resolution measurements, line identification, and spectral modeling of Kα transitions in Fe xviii–Fe xxv. Astrophys. J. 409, 846–859 (1993)

    ADS  CAS  Article  Google Scholar 

  36. 36

    Smith, A. J. et al. spectra of heliumlike iron from tokomak-fusion-test-reactor plasmas. Phys. Rev. A 47, 3073–3079 (1993)

    ADS  CAS  Article  Google Scholar 

  37. 37

    Johnson, W. R. & Soff, G. The lamb shift in hydrogen-like atoms, 1 ≤ Z ≤ 110. Atom. Data Nucl. Data 33, 405–446 (1985)

    ADS  CAS  Article  Google Scholar 

Download references


We acknowledge all the JAXA members who have contributed to the ASTRO-H (Hitomi) project. All US members gratefully acknowledge support through the NASA Science Mission Directorate. Stanford and SLAC members acknowledge support via DoE contract to SLAC National Accelerator Laboratory DE-AC3-76SF00515 and NASA grant NNX15AM19G. Part of this work was performed under the auspices of the US DoE by LLNL under contract DE-AC52-07NA27344 and also supported by NASA grants to LLNL. Support from the European Space Agency is gratefully acknowledged. French members acknowledge support from CNES, the Centre National d’Etudes Spatiales. SRON is supported by NWO, the Netherlands Organization for Scientific Research. The Swiss team acknowledges support of the Swiss Secretariat for Education, Research and Innovation SERI and ESA’s PRODEX programme. The Canadian Space Agency is acknowledged for the support of Canadian members. We acknowledge support from JSPS/MEXT KAKENHI grant numbers 15H02070, 15K05107, 23340071, 26109506, 24103002, 25400236, 25800119, 25400237, 25287042, 24540229, 25105516, 23540280, 25400235, 25247028, 26800095, 25400231, 25247028, 26220703, 24105007, 23340055, 15H00773, 23000004, 15H02090, 15K17610, 15H05438, 15H00785 and 24540232. H. Akamatsu acknowledges support of NWO via a Veni grant. M. Axelsson acknowledges a JSPS International Research Fellowship. C. Done acknowledges STFC funding under grant ST/L00075X/1. P. Gandhi acknowledges a JAXA International Top Young Fellowship and UK Science and Technology Funding Council (STFC) grant ST/J003697/2. H. Russell, A. C. Fabian and C. Pinto acknowledge support from ERC Advanced Grant Feedback 340442. We thank contributions by many companies, including, in particular, NEC, Mitsubishi Heavy Industries, Sumitomo Heavy Industries and Japan Aviation Electronics Industry. Finally, we acknowledge strong support from the following engineers. JAXA/ISAS: C. Baluta, N. Bando, A. Harayama, K. Hirose, K. Ishimura, N. Iwata, T. Kawano, S. Kawasaki, K. Minesugi, C. Natsukari, H. Ogawa, M. Ogawa, M. Ohta, T. Okazaki, S.-i. Sakai, Y. Shibano, M. Shida, T. Shimada, A. Wada, T. Yamada; JAXA/TKSC: A. Okamoto, Y. Sato, K. Shinozaki, H. Sugita; Chubu U: Y. Namba; Ehime U: K. Ogi; Kochi U of Technology: T. Kosaka; Miyazaki U: Y. Nishioka; Nagoya U: H. Nagano; NASA/GSFC: T. Bialas, K. Boyce, E. Canavan, M. DiPirro, M. Kimball, C. Masters, D. Mcguinness, J. Miko, T. Muench, J. Pontius, P. Shirron, C. Simmons, G. Sneiderman, T. Watanabe; Noqsi Aerospace Ltd: J. Doty; Stanford U/KIPAC: M. Asai, K. Gilmore; ESA (Netherlands): C. Jewell; SRON: D. Haas, M. Frericks, P. Laubert, P. Lowes; U of Geneva: P. Azzarello; CSA: A. Koujelev, F. Moroso.

Author information




The science goals of Hitomi (known as ASTRO-H before launch) were discussed and developed over more than 10 years by the ASTRO-H Science Working Group (SWG), all members of which are authors of this manuscript. All the instruments were prepared by joint efforts of the team. Calibration of the Perseus dataset was carried out by members of the SXS team. Data analysis and manuscript preparation were carried out by a small subgroup of authors appointed by the SWG, on the basis of the extensive discussion made in the white paper produced by all SWG members. The manuscript was subject to an internal collaboration-wide review process. All authors reviewed and approved the final version of the manuscript.

Corresponding author

Correspondence to Andrew C. Fabian.

Extended data figures and tables

Extended Data Figure 1 SXS spectrum of the full field overlaid with a CCD spectrum of the same region.

The CCD is the Suzaku X-ray imaging spectrometer (XIS) (red line); the difference in the continuum slope is due to differences in the effective areas of the instruments.

Extended Data Figure 2 The iron line complexes from the outer region compared with best-fit models.

ac, These have been obtained from various emission-line databases typically used in the literature. The spectra were modelled as a single-temperature, optically thin plasma in collisional ionization equilibrium using either APEC/ATOMDB 3.0.3 (ref 16; red) or SPEX 3.0 (ref. 17; blue). We determined the best-fit model by fitting the Hitomi spectrum from the outer 23 pixels in the energy range 6.4–8 keV, excluding the Fe Heα resonance line and Ni Heα line complex. We obtain consistent best-fit parameters, with both APEC and SPEX predicting a temperature of 4.1 ± 0.1 keV. The iron-to-hydrogen abundances are 0.62 ± 0.02 from APEC and 0.74 ± 0.02 from SPEX, relative to solar values31. The line broadening obtained from APEC, 146 ± 7 km s−1, is smaller than the best-fit SPEX value of 171 ± 7 km s−1, although both values are consistent with the line broadening obtained by fitting a set of Gaussians (the result presented in the main body of the paper). Apart from the Fe Heα w line affected by resonance scattering (a), both emission line models presented here currently have difficulty reproducing the measured Fe Heα intercombination lines (a) as well as the exact position of the Fe Heβ line (c). This motivates the model-independent approach adopted in the manuscript for determining the line widths. Error bars are 1 s.d.

Extended Data Figure 3 The Fe He-α line complex from the central region around the AGN.

The 5.0–8.5-keV spectrum was modelled with an isothermal, optically thin plasma in collisional ionization equilibrium using either APEC/ATOMDB 3.0.3 (red) or SPEX 3.0 (blue), with an additional power-law component accounting for emission from the central AGN. During the fit we excluded the Fe Heα resonance line because this can be affected by resonant scattering of photons by the intracluster gas in the line of sight. The two spectral codes provide similar results with an average temperature of 3.8 ± 0.1 keV and metallicity consistent with the solar value. We obtain a velocity broadening of 156 ± 12 km s−1 from APEC and 178 ± 9 km s−1 from SPEX. Both models suggest that the resonant line has been suppressed in the central region. Error bars are 1 s.d.

Extended Data Figure 4 Confidence contours for joint fits of redshift z and velocity broadening σv are compared.

The three line complexes have been fitted independently. The contours are plotted at (68%, two parameters) and (95%). The three fits give consistent redshifts (with the one to which the data were self-calibrated) and broadening.

Extended Data Figure 5 The spatial response of the SXS array.

The total broadband counts (colour scale) seen across the detector array (left), Fe Heα line counts (centre) that come mostly from the diffuse cluster plasma, and a model response of a point source centred in the pixel coincident with the nucleus of NGC 1275 (right) are compared. Brightness is normalized to the same peak value.

Extended Data Figure 6 The line-of-sight gas velocities overlaid on a deep Chandra image.

The Chandra image is from ref. 32. The contours increase by a factor of 1.5. The numbers in the larger font indicate the velocity in each region (see also the colour scale). The 90% errors in the figure (numbers in the smaller font) are statistical only; our estimate of the calibration uncertainty in individual pixels is 50 km s−1. Heliocentric correction has been applied. Velocities are shown relative to that of NGC 1275, whose redshift is z = 0.01756 (ref. 33).

Extended Data Figure 7 The SXS field overlaid on the cold gas nebulosity surrounding NGC 1275.

The image shows Hα emission34. The radial velocity along the long northern filament measured from CO data21 decreases, south to north (within the SXS field of view), from about +50 km s−1 to −65 km s−1. This is similar to the trend seen in the SXS velocity map (Extended Data Fig. 6).

Extended Data Figure 8 In-flight spectral resolution of the SXS.

a, The composite spectrum of all pixels (excluding the calibration pixel) when they were exposed to the 55Fe source on the filter wheel. The blue line shows the expected natural line shape and the red line shows the observed profile (error bars are 1 s.d.). b, A histogram of pixel resolution. N is the number of pixels sharing that resolution.

Extended Data Table 1 Line energies used in the Gaussian fits

Related audio

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Hitomi Collaboration. The quiescent intracluster medium in the core of the Perseus cluster. Nature 535, 117–121 (2016).

Download citation

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


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