Tuesday, July 27, 2021

The Laguna Nebula

The Laguna Nebula (Messier 8, NGC 6523) is a gigantic interstellar cloud in the constellation Sagittarius.  It is classified as an emission nebula, whose ionized gases, mainly hydrogen, emit radiation mainly in the wavelength range of visible red light.

 One of the main features of the Laguna nebula is the presence of black nebulae known as Bok's globules, which are protostellar clouds with diameters of about 10,000 AU.  Some of the most prominent globules were listed by Edward Barnard in his catalog of dark nebulae, including Barnard 88 (B 88), a comet-shaped globule, B 89, in the region of the NGC 6530 cluster, and B 296.

 The brightest region of the nebula, discovered by John Herschel and known as the Hourglass Nebula, is a region where intense star formation occurs: the intense luminous emission is caused by the excitation of hot young stars, mainly by the star Herschel 36, of magnitude apparent 9.5 and spectral class O7.  Very close to the Nebula's bright region is the object's brightest star, 9 Sagittarii, with apparent magnitude 5.97 and spectral class O5, which accounts for much of the nebula's brightness.

 The open cluster associated with the nebula, NGC 6530, belongs to class II.2.m.n, according to Robert Julius Trumpler's classification of open clusters, where class I refers to the denser clusters and class IV to the less dense ones;  class 1 to agglomerates with little difference in brightness between its components and class 3 to those with a large difference in brightness;  and class p for star-poor clusters, m for clusters with the number of stars within the average, and r for star-rich clusters.  Despite having a nucleus, the stars belonging to the cluster are very sparse: there are 50 to 100 stars associated with the interstellar cloud of the Laguna nebula.  Its brightest star belongs to the spectral class O5 and has an apparent magnitude of 6.9.  According to Eichler, the cluster is about 2 million years old and, according to Woldemar Götz, the cluster has an extremely bright class Of star belonging to the spectral class O, but which contains spectral lines of helium and nitrogen.

 In 2006, the first four Herbig-Haro objects in the nebula, including object HH ​​870, the first direct evidence of active star formation by matter accretion. 

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