Astronomy

This picture shows galaxy ESO 593-IG 008, or IRAS 19115-2124. The previously taken Hubble images shows that the object are colliding two galaxies — one a barred spiral, and the other is more irregular. But recent observation with ESO’s Very Large Telescope made clear identification of a third, separate component, an irregular, yet fairly massive galaxy that seems to be forming stars at a frantic rate.

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 extend more than 100,000 light-years, or the size of our own Milky Way.

Subsequent optical spectroscopy with the new Southern African Large Telescope, and archive mid-infrared data from the NASA’s Spitzer Space Telescope, confirmed the separate nature of the ‘head’. It also revealed that 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. 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 quiescent epoch of their interaction-induced star formation history.

The ‘Bird’ belongs to the prestigious 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, such as mergers of galaxies, which in turn trigger bursts of star formation, and may eventually lead to the formation of a single elliptical galaxy.

Image credits: ESO/Henri Boffin.

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