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LHA 115-N 76A
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Name: LHA 115-N 76A
Description: Nebula
Position (J2000): RA 1h 3m 48.92s Dec -72° 3' 51.42"
Constellation: Tucana
Distance: 180000 light years
Field of view: 6.57 x 6.57 arcminutes
Orientation: North is 0.1° left of vertical
Image Credit: ESO
Release Date: April 9, 2003

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Quite a few of the most beautiful objects in the Universe are still shrouded in mystery. Even though most of the nebulae of gas and dust in our vicinity are now rather well understood, there are some which continue to puzzle astronomers. This is the case of a small number of unusual nebulae that appear to be the subject of strong heating - in astronomical terminology, they present an amazingly "high degree of excitation." This is because they contain significant amounts of ions, i.e., atoms that have lost one or more of their electrons. Depending on the atoms involved and the number of electrons lost, this process bears witness to the strength of the radiation or to the impact of energetic particles. But what are the sources of that excitation? Could it be energetic stars or perhaps some kind of exotic objects inside these nebulae? How do these peculiar objects fit into the current picture of universal evolution? New observations of a number of such unusual nebulae have recently been obtained with the Very Large Telescope (VLT) at the ESO Paranal Observatory (Chile).

This unique image shows LHA 115-N 76A, the nebula surrounding the Wolf-Rayet star AB7. This is one of the highest excitation nebulae in the Magellanic Clouds, two satellite galaxies of our own Milky Way. AB7 is a binary star, consisting of one WR-star - highly evolved massive star - and a mid-age massive companion of spectral type O. These exceptional stars have very strong stellar winds : they continuously eject energetic particles - like the "solar wind" from the Sun - but some 10 to 1,000 million times more intensely than our sun! These powerful winds exert an enormous pressure on the surrounding interstellar material and forcefully shape those clouds into "bubbles", well visible in the photos by their blue color.

AB7 is particularly remarkable: the associated huge nebula and HeII region indicate that this star is one of the, if not THE, hottest WR-star known so far, with a surface temperature in excess of 120,000 degrees! Just outside this nebula, a small network of green filaments is visible - they are the remains of another supernova explosion.