Astronomers spot elusive bird shaped triple cosmic collision

December 21st, 2007 - 2:37 pm ICT by admin  

Munich, Dec 21 (ANI): A very rare case of a bird shaped collision of three galaxies, has been spotted by astronomers using ESOs (European Southern Observatory) Very Large Telescope.

Because of the resemblance of the system to a bird, the object was dubbed as such, with the ‘head’ being the third component, and the ‘heart’ and ‘body’ making the two major galaxy nuclei in-between of tidal tails, the ‘wings’. The latter extends more than 100,000 light-years, or the size of our own Milky Way.

Comprising of two massive spiral galaxies and a third irregular galaxy, the merger was previously known just as an interacting pair of galaxies at a distance of 650 million light-years.

But observations made with the NACO instrument attached to ESO’s VLT, revealed all-pervasive dust clouds under the galaxies, using adaptive optics to resolve the finest details.

The NACO images show two unmistakable galaxies, one a barred spiral while the other is more irregular.

But, the surprise lay in the clear identification of a third, clearly separate component, an irregular, yet fairly massive galaxy termed the head, that seems to be forming stars at a frantic rate.

The ‘head’ is forming stars violently, at a rate of nearly 200 solar masses per year, while the other two galaxies appear to be at a more dormant epoch of their interaction-induced star formation history.

“Examples of mergers of three galaxies of roughly similar sizes are rare,” says Petri Vaisanen, lead author of the paper reporting the results. “Only the near-infrared VLT observations made it possible to identify the triple merger nature of the system in this case,” he added.

Subsequent optical spectroscopy with the new Southern African Large Telescope, and archive mid-infrared data from the NASA Spitzer space observatory, confirmed the separate nature of the ‘head’ in this bird shaped system.

It also added to further surprises.

For example, the ‘head’ and major parts of the ‘Bird’ are moving apart at more than 400 km/s (1.4 million km/h!). Observing such high velocities is very rare in merging galaxies. Also, the ‘head’ appears to be the major source of infrared luminosity in the system, though it is the smallest of the three galaxies.

“It seems that NACO has caught the action right at the time of the first high-speed fly-by of the ‘head’ galaxy through the system consisting of the other two galaxies,” said Seppo Mattila, member of the discovery team. “These two galaxies must have met earlier, probably a couple of hundred million years ago,” he added.

The ‘Bird’ belongs to the family of luminous infrared galaxies, with an infrared luminosity nearly one thousand billion times that of the Sun. This family of galaxies has long been thought to signpost important events in galaxy evolution. (ANI)

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