  Very massive stars, 100 times heavier than the sun, are rare. It is not yet
known whether such stars can form in isolation or only in star clusters. The
answer to this question is of fundamental importance. The central region of our
Galaxy is ideal for investigating very massive stars and clusters located in
the same environment. We used archival infrared images to investigate the
surroundings of apparently isolated massive stars presently known in the
Galactic Center. We find that two such isolated massive stars display apparent
bow shocks and hence may be "runaways" from their birthplace. Thus, some
isolated massive stars in the Galactic Center region might have been born in
star clusters known in this region. However, no bow shock is detected around
the isolated star WR102ka (Peony nebula star), which is one of the most massive
and luminous stars in the Galaxy. This star is located at the center of an
associated dusty circumstellar nebula. To study whether a star cluster may be
"hidden" in the surroundings of WR102ka, to obtain new and better spectra of
this star, and to measure its radial velocity, we obtained observations with
the integral-field spectrograph SINFONI at the ESO's Very Large Telescope
(VLT). Our observations confirm that WR102ka is one of the most massive stars
in the Galaxy and reveal that this star is not associated with a star cluster.
We suggest that WR102ka has been born in relative isolation, outside of any
massive star cluster.
