Omega Nebula

Lore & Background

The Omega Nebula is an H II region in Sagittarius, discovered by Philippe Loys de Chéseaux in 1745 and catalogued by Charles Messier in 1764. It is between 5,000 and 6,000 light-years from Earth and spans some 15 light-years in diameter. The cloud of interstellar matter of which this nebula is a part is roughly 40 light-years in diameter and has a mass of 30,000 solar masses, while the total mass of the Omega Nebula itself is an estimated 800 solar masses. Its local geometry is similar to the Orion Nebula except that it is viewed edge-on rather than face-on.

The open cluster NGC 6618 lies embedded in the nebulosity and causes the gases of the nebula to shine due to radiation from hot, young stars; the actual number of stars in the nebula is much higher – up to 800, 100 of spectral type earlier than B9, and 9 of spectral type O, plus over a thousand stars in formation on its outer regions. It is one of the youngest clusters known, with an age of just 1 million years. The luminous blue variable HD 168607, in the south-east part of the nebula, is generally assumed to be associated with it; its close neighbor, the blue hypergiant HD 168625, may be too. The Swan portion of M17 is said to resemble a barber's pole.

Early research included the first attempt to accurately draw the nebula by John Herschel in 1833, published in 1836, who described its figure as nearly that of a Greek capital omega, Ω, somewhat distorted. A second sketch was made during his visit to South Africa in 1837. The nebula was also studied by Johann von Lamont and separately by an undergraduate at Yale College, Mr Mason, starting from around 1836. Herschel noted possible changes in brightness but also conflicting testimony from Mr Mason. Sketches were also made by William Lassell in 1862 and by M. Trouvelot and Edward Singleton Holden in 1875.

Reader's Guide

The Omega Nebula is notable as one of the brightest and most massive star-forming regions of our galaxy, catalogued by Charles Messier in 1764. Its embedded open cluster NGC 6618, with an age of just 1 million years, makes it one of the youngest known clusters. The nebula's distinctive shape, likened to a Greek capital omega, was first accurately drawn by John Herschel in 1833, and subsequent observations by Herschel, Johann von Lamont, Mr Mason, William Lassell, M. Trouvelot, and Edward Singleton Holden contributed to its early study. In January 2020, the Stratospheric Observatory for Infrared Astronomy (SOFIA) provided new insights, revealing nine previously unseen protostars primarily in the southern regions and suggesting that parts of the nebula formed separately, contributing to its distinctive swan-like shape. The nebula is also associated with the luminous blue variable HD 168607 and possibly the blue hypergiant HD 168625.

Did You Know?

• It contains up to 800 stars, including 9 of spectral type O, and over a thousand stars in formation on its outer regions.
• In January 2020, SOFIA discovered nine previously unseen protostars in the nebula.
• The nebula's shape was first compared to a Greek capital omega by John Herschel in 1833.