ISO UNVEILS THE COLD SKELETON OF ANDROMEDA
The Andromeda galaxy, also called M31, is one of the closest companion of our own galaxy, at only two million light-years away. It has been always considered a well known typical spiral galaxy, but the European Space Agency's ISO infrared telescope shows that Andromeda is made of several concentric rings: M31 looks really like a ringed galaxy.The rings are made of dust at a temperature considerably colder than previous estimates --at about -260 degree C--, which poses a new problem for the astronomers to explain. This kind of material cannot be seen by optical telescopes and thus in the common views of Andromeda the rings are invisible, while they become bright in the infrared.
In the face-on deprojection produced by the scientists to enhance the galaxy's features no obvious spiral pattern is recognisable. The cold main ring clearly dominates the structure: a large fraction of the dust of the whole galaxy gathers there, and many new stars are being born.
"The overall far-infrared morphology of M31 can be described as a multiple ringed galaxy rather than the classical spiral type found in the optical", main author Martin Haas explains in the article published this month in scientific journal 'Astronomy and Astrophysics'. However, in the future the rings might become prominent in the optical as well, if more stars keep being born in the dust: "Andromeda might be undergoing a transition phase", Haas says.
Credits: ESA/ISO/ISOPHOT and M. Haas D. Lemke, M. Stickel, H. Hippelein, et al.
This observation was discussed in details in a ISO/ESA Information Note, Nr 33-98;
The images are also available in high-resolution (300 dpi) Postscript images :
| ISO 175 µ map of M31: | Postscript compressed |
| Face-on deprojection of the ISO 175 µ map of M31: | Postscript compressed |