Barnard's Loop

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Long exposure of the constellation Orion with glowing red clouds of ionized hydrogen ( H-alpha ). The semicircular arc on the left is Barnard's Loop.

Barnard's Loop (catalog name: Sh 2-276 ; German: Barnard's loop ) is a large, O-shaped emission nebula in the constellation Orion . It belongs to an extensive interstellar cloud in which, as can be determined by infrared astronomy , star formation is constantly taking place. Barnard's Loop is part of the Orion Molecular Cloud Complex .

The nebula is in the form of an extended but faint loop that is too weakly lit to be visible to the naked eye. It can only be captured photographically when the sky is very dark or with large astrographs . Barnard's Loop stretches around the belt stars and the Orion Nebula , the stars of which are presumably responsible for the ionization of the gas , in a wide arc of 10 to 15 ° in diameter starting north of the Orion Belt . To the south, Barnard's Loop extends almost to the bright star Rigel at the foot of Orion.

The vast H-II area is 1,500–1600 light years away, measures about 300 light years in diameter and would fill almost the entire constellation in the infrared. In with dark mist interspersed, luminous gas and molecular cloud (engl. Giant molecular cloud , GMC) will be in the next year, millions by shock waves and magnetic interactions numerous bright star form and a short-lived cluster shapes.

Explanatory models

The formation of Barnard's Loop was presumably triggered by a supernova 2 million years ago, which could also lead to the formation of some stars in the constellations Carter and Aries . Other astronomers regard the nebula as the direct remainder of a supernova because of its pale ring shape, or attribute the formation of its H-II region to the stellar wind of some young stars because the trapezoidal stars are roughly in the center of the arc.

It could also be the ionized inner surface of a much larger gas cloud. In any case, this large “interstellar bubble” reveals some interactions between the interstellar medium and nearby stars.

Observations in ultraviolet light show that Barnard's Loop not only shines itself, but also in the scattered starlight. As a reflection nebula , its greatest intensity coincides with the spectra of the young O and B stars in the Orion Nebula. Some parts of the reflection nebula measure almost 30 ° (?) In diameter, with which they exceed the already large HII component by four times.

Associated fog in the area

Nearby - just south of the left belt star Alnitak - is the well-known Horsehead Nebula . It gets its outline from the head-shaped dark cloud directly in front of an emission nebula and is related to Barnard's Loop.

The nearby Orion Nebula ( M 42 ) is also a birthplace for young stars. The Hubble Space Telescope has discovered numerous protoplanetary disks here , some of which may lead to planet formation.

Inside Barnard's Loop there are more small gas nebulae near the right belt star. About 10 ° to the side of Orion is the roughly equally bright and also reddish, but smaller Rosette Nebula NGC 2237.

Discovery and Visibility

The nebula was discovered in 1895 by Edward Barnard at the Yerkes Observatory on a photo plate made with a portrait camera only about 8 inches tall .

Wilhelm Herschel probably saw the lighter parts of Barnard's Loop in 1786. While the fog can be recognized photographically with a telephoto lens from an exposure time of around 10 minutes , with today's light pollution it visually requires a nebula filter in addition to a powerful telescope . Lighter areas in the loop then appear as diffuse background lights.

See also

Footnotes

  1. ↑ Photo F.Gruber ( Memento of 20 May 2006 at the Internet Archive )

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