Cosmic methanol ring

The question how a massive star is being born is one of the most interesting topic in modern astrophysics. Young stars are hidden in interstellar matter and their light is not able to escape from dense clouds of dust and gas. Some information from newly born stars (so called protostars) can be obtained from infra-red (0.1 mm wavelength) and radio waves (a few cm waves). However, the unique tool in studies of massive star formation is the methanol (CH3OH) maser emission. Such methyl alcohol chemicals arise in close environment of a massive protostar and can emit 5 cm wavelengths which are amplified and lead to a maser emission. Due to its brightness the maser can be detected quite easily from the furthest regions of the Milky Way or even from other galaxies.

10 hour European VLBI Network session taken on 11 November 2004 was particularly fruitful for astronomers from Centre for Astronomy in Torun. They used 8 radio telescopes from Germany, Italy, the Netherlands, Poland, Sweden, the United Kingdom and for the first time discovered the methanol maser emission with ring-like distribution towards star forming regions G23.657-0.127.
Such circular structure of methanol maser in star forming regions has been searched by astronomers all over the world for a few years. The EVN has
recently increased the number of antennas with receivers of 5 cm radio waves. This allowed them to imaged relatively weak methanol emission towards G23.657-0.127. The ring-like morphology strongly suggests the existence of a central object – a young OB star that is not seen in the visible wavelength. The distance to that star is estimated from the trigonometric parallax measurements using Very Long Baseline Array (VLBA) and is 3190 pc (i.e. 10.000 light years, which is one tenth of a size of our Milky Way). The radius of the ring is about 405 AU (about 10 times larger than the Sun-Pluto distance). The origin of this structure is still not clear. It can be related to a circumstellar disc around a young star that we face-on, or an outflow directed to us, or a radial shock(s) driven by the central OB star. Other observations support the hypothesis that the newly discovered object is related to a young protostar which is a real newborn infant in the massive star life cycle.

paralaksa_ra paralaksa_dec_eng

Position offsets of four maser ring components in right ascension and declination due to the annual parallax and the best fit model indicating the parallax of 0.313 milliarcsecond which corresponds to a distance of 3190 pc.


Original publications:
Bartkiewicz A., Szymczak M. and van Langevelde H.J., Astronomy and
Astrophysics Letters, 2005, 442, 61
Bartkiewicz A., Brunthaler A., Szymczak M., van Langevelde H.J. and Reid
M.J., Astronomy and Astrophysics, 2008, 490, 787

dr. Anna Bartkiewicz, e-mail: email text
prof. Marian Szymczak, e-mail: email text