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Three classical Cepheid variable stars in the nuclear bulge of the Milky Way


The nuclear bulge is a region with a radius of about 200 parsecs around the centre of the Milky Way1. It contains stars with ages2,3,4 ranging from a few million years to over a billion years, yet its star-formation history and the triggering process for star formation remain to be resolved. Recently, episodic star formation, powered by changes in the gas content, has been suggested5. Classical Cepheid variable stars have pulsation periods that decrease with increasing age6, so it is possible to probe the star-formation history on the basis of the distribution of their periods7,8. Here we report the presence of three classical Cepheids in the nuclear bulge with pulsation periods of approximately 20 days, within 40 parsecs (projected distance) of the central black hole. No Cepheids with longer or shorter periods were found. We infer that there was a period about 25 million years ago, and possibly lasting until recently, in which star formation increased relative to the period of 30–70 million years ago.

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Figure 1: The classical Cepheids discovered in the Nuclear Bulge.
Figure 2: Period distribution of the nuclear bulge Cepheids and those previously found in the Milky Way.
Figure 3: Star-formation history in the nuclear bulge during the last hundred million years.

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We thank the IRSF/SIRIUS team in Nagoya University, the National Astronomical Observatory of Japan, Kyoto University and the University of Tokyo, and the staff of the South African Astronomical Observatory (SAAO) for their support during our near-IR observations. This work was supported by Grants-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (JSPS). M.W.F. acknowledges the support from National Research Foundation (NRF) of South Africa.

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Correspondence to Noriyuki Matsunaga.

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Matsunaga, N., Kawadu, T., Nishiyama, S. et al. Three classical Cepheid variable stars in the nuclear bulge of the Milky Way. Nature 477, 188–190 (2011).

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