Anne’s Picture of the Day: Emission Nebula LHA 120-N 44

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February 9, 2012

LHA 120-N 44, an emission nebula in the LMC

Image Credit: ESO

LHA 120-N 44 (or N44 for short) is an emission nebula (H II region) of some 1,000 light-years across, located about 157,000 light-years away in the Large Magellanic Cloud, a satellite galaxy of our own Milky Way, toward the southern constellation of Dorado.

This very rich region of gas, dust and young stars surrounds NGC 1929, a rich large cluster of bright young, blue-white stars, and is without doubt the original source of the material that formed these stars that produce intense radiation.

LHA 120-N 44 is dominated by a cosmic superbubble. This superbubble, of roughly 325 by 250 light-years across, is expanding outwards due to an interaction between two destructive forces generated by the stars at its center: Young stars in the cluster send out streams of charged particles (or stellar winds) that have cleared out the bubble center, and massive stars have exploded to create supernovae shock waves that push the gas out further.

LHA 120-N 44 has a smaller bubble structure inside known as N44F which has been shaped in a similar manner; it has a hot, massive central star with an unusually powerful stellar wind that moves at 7 million kilometers per hour. This is because it loses material at 100 million times the rate of the Sun, or approximately 1,000,000,000,000,000 tons per year.

Multiple smaller bubbles appear in the image as bulbous growths clinging to the central superbubble. Most of these regions were probably formed as part of the same process that shaped the central cluster. Their formation could also have been “sparked” by compression of the surrounding material as the central stars pushed the surrounding gas outward.

However, varying density in LHA 120-N 44 has caused the formation of several dust pillars that may conceal star formation. This variable density is likely caused by previous supernovae in the vicinity of the nebula; many of the stars that have shaped it will eventually also end as supernovae. The past effects of supernovae are also confirmed by the fact that N44 emits x-rays.

This picture of the southern part of N44 is based on three images taken on 6 and 7 December 2001 with the Wide-Field-Imager at the ESO/MPG 2.2-m telescope. The green colour indicates areas that are particularly hot.

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