N11, frantic star formation

 

 

 

 

 

 

 

Just right of the center of this image lies LHA 120-N 11, the “Bean Nebula”, a large (about 1,000 light years across) emission nebula located in the outskirts of the Large Magellanic Cloud (LMC). The annotated image, below, shows several other objects in this field. N11 is considered to be the nebula with the second largest star-birth rate in the LMC (just after 30 Doradus, the Tarantula Nebula). The whitish areas do really have this color. The Oxygen emission is as intense as the Hydrogen one, and the balanced mix of RGB for these filters, provides a neat white. The greenish-blue regions are stronger in Oxygen emission.

LHA 120-N11 (also called LH 10) is a vast, multi-shell H II complex in the northwest of the Large Magellanic Cloud and is widely recognized as the second-largest star-forming region in the galaxy, surpassed only by 30 Doradus (the Tarantula Nebula). Its evacuated central cavity and bright surrounding rims trace intense stellar feedback—ionizing radiation, winds, and past supernovae—from the massive OB stars. The strong stellar winds generated by these newborns, will totally change the shape and aspect of this region within the next couple of million years.

Star formation in N11 proceeds sequentially. The central OB association LH 9 (central open cluster) appears older and has already cleared much of its natal gas; younger activity is concentrated in LH 10 (N11 itself) and LH 13 (also called NGC 1769, the nebula just above-left of N11). This is consistent with triggered star formation as by the shock fronts that compress surrounding clouds. Deep optical photometry and spectroscopy resolve rich pre-main-sequence populations and age gradients that support this feedback-driven scenario.

Not surprising, the cold and dense reservoirs that feed new stars are mapped in rotational lines of CO. High-resolution observations reveal clumpy molecular clouds and shell-like structures around the cavity, indicating that winds from earlier generations have re-organized the interstellar medium and promoted subsequent collapse at the periphery. These data, together with mid-IR imaging, tie current star formation to swept-up shells and pillars exposed to strong UV fields.  N11’s hot phase is also giving us a lot of fresh information: recent X-ray analyses find diffuse, million-degree gas filling bubbles and superbubbles. The compact nebulae such as N11 currently show ongoing further star formation around very young massive stars; HST has been able to resolve their internal ionized structures and dust pillars.