독수리 성운, 별 여왕 성운

Messier 16, NGC 6611 - Eagle Nebula, Star Queen Nebula

Messier 16 is a conspicuous region of active star formation, appearing in the constellation Serpens Cauda. This giant cloud of interstellar gas and dust is commonly known as the Eagle Nebula, and has already created a cluster of young stars. The nebula is also referred to the Star Queen Nebula and as IC 4703; the cluster is NGC 6611.

Discovery and Observation

The cluster was discovered by Philippe Loys de Cheseaux in 1745-1746, who made no mention of the nebula. Charles Messier independently rediscovered the cluster in 1764, and described its stars as "enmeshed in a faint glow", suggesting that he discovered the nebula as well.

The Herschels apparently did not perceive the nebula, so their catalogs (and consequently the NGC) only describe the cluster. The nebula was probably first photographed by E.E. Barnard in 1895, or by Isaac Roberts in 1897. From Roberts's finding, the nebula was added to the second Index Catalog in 1908 as IC 4703, "with cluster M 16 involved".

M 16 is found rather easily, close to Serpens Cauda's borders with Scutum and Sagittarius. Starting from Altair (α Aquilae), follow δ and λ Aql to Gamma Scuti; M 16 is about 2-1/2° west of this star. The Omega Nebula (M 17) is 2° SW of γ Sct.

With an overall visual magnitude of 6.4, and an apparent diameter of 7', the Eagle Nebula's star cluster is best seen with low power telescopes. The brightest star in the cluster has an apparent magnitude of +8.24, easily visible with good binoculars. A 4" scope reveals about 20 stars in an uneven background of fainter stars and nebulosity; three nebulous concentrations can be glimpsed under good conditions. Under very good conditions, suggestions of dark obscuring matter can be seen to the north of the cluster.

In an 8" telescope at low power, M 16 is an impressive object. The nebula extends much farther out, to a diameter of over 30'. It is filled with dark regions and globules, including a peculiar dark column and a luminous rim around the cluster. The outlines of the nebula are sometimes said to look like a three-leaf clover.

The Eagle nebula is best seen on photographs, but larger apertures and O-III filters may help to trace some detail visually. More dark pillars, also known as "elephant trunks", can be seen in large amateur instruments (12" and larger aperture).

Properties and Evolution

The Eagle Nebula lies some 7,000 light years away in the Sagittarius-Carina spiral arm of our galaxy - the next arm inward from us. At this distance, the cluster's angular diameter corresponds to a linear size of about 15 light years. The nebula extends much farther out, to dimensions of about 70 x 55 light years. M 16 might form one giant complex with M 17, the Omega Nebula, to the south in Sagittarius.

M 16's stellar swarm is only about 5.5 million years old, with its hottest, youngest stars of spectral type O6. Excited by high-energy ultraviolet radiation from these massive stars, this great cloud of interstellar gas glows by fluorescence.

by the Hubble Space Telescope.
Images made in 1995 by the Hubble Space Telescope greatly improved our understanding of the star formation process taking place inside the nebula. One of these images, a famous photograph known as the "Pillars of Creation", depicts a large region of star formation whose small dark areas are believed to be protostars. At the end of each pillar, the intense ultraviolet light of newborn stars is vaporizing some of the hydrogen gas, and shaping structures called "EGGs" (Evaporating Gaseous Globules).

In 2007, scientists using the Spitzer Space Telescope discovered evidence that the Pillars were actually destroyed by a supernova explosion about 6,000 years ago. But the light showing their destruction, and the new shape of the nebula, will not reach the Earth for another millennium.