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.

Millimetre-wave emission from an intermediate-mass black hole candidate in the Milky Way


It is widely accepted that black holes with masses greater than a million solar masses (M ) lurk at the centres of massive galaxies. The origins of such ‘supermassive’ black holes (SMBHs) remain unknown1, although those of stellar-mass black holes are well understood. One possible scenario is that intermediate-mass black holes (IMBHs), which are formed by the runaway coalescence of stars in young compact star clusters2, merge at the centre of a galaxy to form a SMBH3. Although many candidates for IMBHs have been proposed, none is accepted as definitive. Recently, we discovered a peculiar molecular cloud, CO–0.40–0.22, with an extremely broad velocity width, near the centre of our Milky Way galaxy. Based on the careful analysis of gas kinematics, we concluded that a compact object with a mass of about 105 M is lurking in this cloud4. Here we report the detection of a point-like continuum source as well as a compact gas clump near the centre of CO–0.40–0.22. This point-like continuum source (CO–0.40–0.22*) has a wide-band spectrum consistent with 1/500 of the Galactic SMBH (Sgr A*) in luminosity. Numerical simulations around a point-like massive object reproduce the kinematics of dense molecular gas well, which suggests that CO–0.40–0.22* is one of the most promising candidates for an intermediate-mass black hole.

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

Relevant articles

Open Access articles citing this article.

Access options

Rent or buy this article

Get just this article for as long as you need it


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

Fig. 1: ALMA views of CO–0.40–0.22.
Fig. 2: Gas kinematics around CO–0.40–0.22*.
Fig. 3: Wide-band spectrum of CO–0.40–0.22*.
Fig. 4: N-body simulations of the gravitational kick.


  1. Djorgovski, S. G., Volonteri, M., Springel, V., Bromm, V. & Meylan, G. in The Eleventh Marcel Grossmann Meeting on Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories (eds Kleinert, H., Jantzen R. T. & Ruffini, R.) 340–367 (World Scientific, 2008)

  2. Portegies Zwart, S. F., Makino, J., McMillan, S. L. W. & Hut, P. Star cluster ecology. III. Runaway collisions in young compact star clusters. Astron. Astrophys. 348, 117–126 (1999).

    ADS  Google Scholar 

  3. Ebisuzaki, T. et al. Missing link found? The ‘runaway’ path to supermassive black holes. Astrophys. J 562, L19–L22 (2001).

    Article  ADS  Google Scholar 

  4. Oka, T., Mizuno, R., Miura, K. & Takekawa, S. Signature of an intermediate-mass black hole in the central molecular zone of our Galaxy. Astrophys. J. 816, L7 (2016).

    Article  ADS  Google Scholar 

  5. Oka, T. et al. ASTE CO J = 3–2 survey of the Galactic Center. Astrophys. J. Suppl. 201, 14–25 (2012).

    Article  ADS  Google Scholar 

  6. Oka, T., Hasegawa, T., Sato, F., Tsuboi, M. & Miyazaki, A. A large-scale CO survey of the Galactic Center. Astrophys. J. Suppl. 118, 455–515 (1998).

    Article  ADS  Google Scholar 

  7. Oka, T. et al. A high-velocity molecular cloud near the center of the Galaxy. Astrophys. J. 515, 249–255 (1999).

    Article  ADS  Google Scholar 

  8. Oka, T., Hasegawa, T., Sato, F., Tsuboi, M. & Miyazaki, A. A hyperenergetic CO shell in the Galactic Center molecular cloud complex. Publ. Astron. Soc. Japan 53, 787–791 (2001).

    Article  ADS  Google Scholar 

  9. Maillard, J. P., Paumard, T., Stolovy, S. R. & Rigaut, F. The nature of the Galactic Center source IRS 13 revealed by high spatial resolution in the infrared. Astron. Astrophys. 423, 155–167 (2004).

    Article  ADS  Google Scholar 

  10. Schödel, R., Eckart, A., Iserlohe, C., Genzel, R. & Ott, T. Black hole in the Galactic Center complex IRS 13E ? Astrophys. J. 625, L111–L114 (2005).

    Article  ADS  Google Scholar 

  11. Gillessen, S. et al. Monitoring stellar orbits around the massive black hole in the Galactic Center. Astrophys. J. 692, 1075–1109 (2009).

    Article  ADS  Google Scholar 

  12. Pierce-Price, D. et al. A deep submillimeter survey of the Galactic Center. Astrophys. J 545, L121–L125 (2000).

    Article  ADS  Google Scholar 

  13. Hatsukade, B. et al. AzTEC/ASTE 1.1-mm survey of the AKARI Deep Field South: source catalogue and number counts. Mon. Not. R. Astron. Soc 411, 102–116 (2011).

    Article  ADS  Google Scholar 

  14. Rybicki G. B., & Lightman A. P. Radiative Processes in Astrophysics (Wiley-VCH, Weinheim, Germany, 1986).

  15. Djorgovski, S. & King, I. R. Surface photometry in cores of globular clusters. Astrophys. J. 277, L49–L52 (1984).

    Article  ADS  Google Scholar 

  16. McLaughlin, D. E. Binding energy and the fundamental plane of globular clusters. Astrophys. J. 539, 618–640 (2000).

    Article  ADS  Google Scholar 

  17. Marchant, A. B. & Shapiro, S. L. Star clusters containing massive, central black holes. III. Evolution calculations. Astrophys. J. 239, 685–704 (1980).

    Article  ADS  Google Scholar 

  18. Marconi, A. & Hunt, L. K. The relation between black hole mass, bulge mass, and near-infrared luminosity. Astrophys. J. 589, L21–L24 (2003).

    Article  ADS  Google Scholar 

  19. Moran, E. C. et al. Black holes in the centers of nearby dwarf galaxies. Astron. J. 148, 136–157 (2014).

    Article  ADS  Google Scholar 

  20. van Loon, J. T. et al. Infrared stellar populations in the central parts of the Milky Way galaxy. Astron. Astrophys. 338, 857–879 (2003).

    Google Scholar 

  21. Sashida, T. et al. Kinematics of shocked molecular gas adjacent to the supernova remnant W44. Astrophys. J. 774, 10–16 (2013).

    Article  ADS  Google Scholar 

  22. Yamada, M. et al. Kinematics of ultra-high-velocity gas in the expanding molecular shell adjacent to the W44 supernova remnant. Astrophys. J. 834, L3 (2017).

    Article  ADS  Google Scholar 

  23. Takekawa, S., Oka, T., Iwata, Y., Tokuyama, S. & Nomura, M. Discovery of two small high-velocity compact clouds in the central 10 parsecs of the Galaxy. Astrophys. J. 843, L11 (2017). 

  24. Agol, E., Kamionkowski, M., Koopmans, Léon, V. E., Blandford & Roger, D. Finding black holes with microlensing. Astrophys. J 576, L131–L135 (2002).

    Article  ADS  Google Scholar 

  25. Corral-Santana, J. M. et al. BlackCAT: a catalogue of stellar-mass black holes in X-ray transients. Astron. Astrophys. 587, A61 (2016).

    Article  Google Scholar 

Download references


This paper makes use of the following ALMA data: ADS/JAO.ALMA#2011.0.01234.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. We thank the ALMA staff for the operation of the array and delivering the qualified data. We also thank S. Nakashima and M. Nobukawa for calculating the upper limit to the X-ray flux, and A. E. Higuchi for helping in ALMA data reduction with CASA. T.O. acknowledges support from JSPS Grant-in-Aid for Scientific Research (B) No. 15H03643.

Author information

Authors and Affiliations



T.O. directed the research, analysed the data and wrote the manuscript. S.Ts. and M.N. performed the model calculation. Y.I. and S.Ta. contributed to the analyses and discussion.

Corresponding author

Correspondence to Tomoharu Oka.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Additional information

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

Rights and permissions

Reprints and Permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Oka, T., Tsujimoto, S., Iwata, Y. et al. Millimetre-wave emission from an intermediate-mass black hole candidate in the Milky Way. Nat Astron 1, 709–712 (2017).

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