M8 – Lagoon Nebula

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Lupe Rioné, Amateur astronomer (Spain)

Type

Emission Nebula

Location

Sagittarius Constellation

Distance

5000 light-years

Size

100 light-years

Emission nebulae: are large clouds of interstellar gas where stars are born. For this reason, this type of nebula is full of young stars. The light from the new stars illuminates and heats the nebula, thus turning it into an Emission Nebula.

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History and discovery

The beautiful M8 (NGC 6533), also known as the Lagoon Nebula, was discovered by the Sicilian Giovanni Battista Hoderna in 1654, who cited it in his catalog of nebulae. This celestial body was also recorded by John Flamsteed in 1680 or Guilleaume Le Gentil in 1747. In 1746, the Swiss astronomer Jean-Philippe de Chéseaux once discovered an open cluster (NGC 6530) inside the nebula. Finally, Charles Messier himself noted it in his catalog on his prolific night of May 23-24, 1764, along with several other celestial bodies.

Although M8 is visible to the naked eye, there is no known mention of this object in antiquity, unlike others such as the Ptolemy Cluster. The name Lagoon Nebula is due to its wide, dark path, which, located in the middle of a gas cloud, divides it into two bright sections. Probably, this nebula is the object that contains more celestial bodies, as we will see below.

M8 – Lagoon Nebulae. Credit: Josep Maria Drucis (2016) (Astrosabadell)

M8 Nebula. Photograph was taken in the light emitted by hydrogen (brown), sulfur (red), and oxygen (blue). Image credit: John Nemcik

Characteristics

Like all emission nebulae, M8 or NGC 6533 is a gigantic HII region, that is, a spectacular cradle of stars. In fact, experts estimate that it is the object that contains the most elements. With a magnitude of 5.8, this incredible nebula boasts many large, hot stars, whose ultraviolet radiation sculpts the gases and cosmic dust, giving it its characteristic shape.

At the center of the nebula is an open cluster, known as NGC 6530. The stars in this cluster are the main sources of excitation of the hydrogen contained in M8, giving it its characteristic brightness. In the cluster there are about 60-90 white stars that seem to be born from the very bowels of the nebula, showing an almost three-dimensional appearance due to their different magnitudes. The two brightest stars in the cluster are known as 9 Sagitarii and HD 164816. Their brightness is extravagant due to the closeness of the dark trough that surrounds them and the proximity of dark clouds. These dark regions are known as Bok Globules, small nebulae formed of dust and very cold gas that contribute to the formation of new stars. Specifically, five Bok Globules are known in M8, and some were cataloged by Edward Emerson Barnard as: B88, B89, B296.

The spectacular image of the central region of the M8 nebula. The photograph was taken by the Hubble Space Telescope. Credit: NASA/ESA

An image combining observations made through three different filters ( B, V, R) with the Danish 1.5m telescope at ESO’s La Silla Observatory, Chile. Credits: ESO/ IDA/ Danish 1.5m/ R. Gendler, U.G. Jorgensen, K. Harpsoe.

On the other hand, the discovery in 2006 of 5 Herbig-Haro objects (nebulae associated with newly formed stars) at the southern edge of the nebula provides much more evidence of ongoing star formation. Known as HH893, HH894, HH895, HH896, HH897, these objects are short-lived bipolar nebulae associated with O-class stars; blue stars with masses 60 times that of the Sun and a luminosity 1,400 times greater. One of them is called Herschel 36. The Herbig-Haro is located within one of the brightest regions of M8, known as the Hourglass (not to be confused with the Hourglass Nebula). Intense star formation activity takes place at this site.

All these characteristics, together with its 100 light-year diameter, make M8 an independent microcosm; a gigantic star-forming region with different areas that also includes NGC 6530, the open cluster in the center of the nebula, and the Bok Globules and the Herbig-Haro objects.

 

M8 Nebulae. Credit: Luis Calle Rorasco

OBSERVATION

Being accessible from both hemispheres, M8 is one of the most beautiful, most studied, and most photographed objects. To find M8, it is enough to look towards “Fi” Sagitarii, tracing a line towards Lambda, without leaving the galactic center. To the naked eye, it will look like a small patch. With astronomical binoculars, minor details can be seen, while with a small telescope it can be observed in all its splendor.

The observation of M8 is fascinating due to its contrast, its rich density of stars, and the dark corridors of absorption clouds that delimit it from northeast to southwest and divide in two the most luminous western part of the cloud. It is important to note that in the center of the Lagoon Nebula the stars of the open cluster NGC 6530 can be seen, where the well-known star 9 Satitarii of magnitude 6 and the bright region is known as the Hourglass, discovered by Herschel, can be seen.

The photograph was taken from Pujalt (Barcelona) with a Canon EOS 3OD camera and Sigma 17-70 lens. This photograph shows the location of the M8 nebula, as well as the spectacular Milky Way in the constellation of Sagittarius. Credit: José Luis Martinez Martinez

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