Press Releases
Aug. 25, 2011

Three classical Cepheids and their impact on the star formation history in the Galactic Nuclear Bulge.

  • Noriyuki Matsunaga (School of Science, University of Tokyo)
  • Naoto Kobayashi (School of Science, University of Tokyo)
  • Takahiro Nagayama (School of Science, Nagoya University)
  • Tetsuya Nagata (School of Science, Kyoto University)
  • Motohide Tamura (National Astronomical Observatory of Japan)
  • Shogo Nishiyama (National Astronomical Observatory of Japan)


The region within a few hundred light years of the central blackhole of our Galaxy, often called the Nuclear Bulge, presents us with various interesting objects and phenomena. We discovered in this region classical Cepheid variable stars, pulsating supergiants, whose ages can be derived accurately from their periods. All three of our Cepheids have pulsation periods near 20 days and ages close to 25 million years, suggesting that active star formation occurred at the period around their births. In contrast, the absence of shorter-period Cepheids shows that the star formation rate was lower between 30 and 70 Myr ago. We suggest that the rate of star formation in this region has changed on a time scale of a few tens of million years possibly due to a stochastic gas inflow into the Nuclear Bulge.

Paper information

Three classical Cepheid variable stars in the Nuclear Bulge of the Milky Way
Matsunaga, N., Kawadu, T., Nishiyama, S., Nagayama, T., Kobayashi, N., Tamura, M., Bono, G., Feast, M. W. & Nagata, T.
Nature (DOI: 11.1038/nature10359, published online on 24 August 2011)
Figure 1

Figure 1.
The finding charts of the classical Cepheids discovered in the Nuclear Bulge. The left panel shows the observed field of 0.33 degree by 0.5 degree. This false-colour image is composed of images, a subset of the data we used in analysis, in three passbands: J (1.25 micron), H (1.63 micron) and Ks (2.14 micron). The data were taken with the Infrared Survey Facility (IRSF) 1.4 m telescope and the SIRIUS near-infrared camera located at South African Astronomical Observatory. North is up and east is left. The three panels on the right side are close-ups, covering 40 arc-second squares around the variable stars discovered.

Figure 2

Figure 2.
The period distribution of the Cepheids in the Nuclear Bulge (red) is compared with that of the previously known Cepheids in the Milky Way (black). The grey-coloured region indicates the period range for which our survey could not reach classical Cepheids in the Nuclear Bulge with typical extinction of 3 magnitudes in the Ks band even if they were there.