The Trifid Nebula (catalogued as Messier 20 or M20 and as NGC 6514) is an H II region in the north-west of Sagittarius in a star-forming region in the Milky Way’s Scutum-Centaurus Arm. It was discovered by Charles Messier on June 5, 1764. Its name means ‘three-lobe’. The object is an unusual combination of an open cluster of stars, an emission nebula (the relatively dense, reddish-pink portion), a reflection nebula (the mainly NNE blue portion), and a dark nebula (the apparent ‘gaps’ in the former that cause the trifurcated appearance, also designated Barnard 85). Viewed through a small telescope, the Trifid Nebula is a bright and peculiar object, and is thus a perennial favorite of amateur astronomers.
The most massive star that has formed in this region is HD 164492A, an O7.5III star with a mass more than 20 times the mass of the Sun. This star is surrounded by a cluster of approximately 3100 young stars. The Trifid Nebula was the subject of an investigation by astronomers using the Hubble Space Telescope in 1997, using filters that isolate emission from hydrogen atoms, ionized sulfur atoms, and doubly ionized oxygen atoms. The images were combined into a false-color composite picture to suggest how the nebula might gaze to the eye.
Discovered by Charles Messier in 1764, M20 is a star-forming nebula located 5,000 light-years away from Earth in the constellation Sagittarius. Also known as the Trifid Nebula, M20 has an apparent magnitude of 6.3 and can be spotted with a small telescope. It is best observed during August. This Hubble image of the Trifid Nebula was taken with Wide Field Camera 3 in 2026 to mark Hubble’s 36th anniversary. Astronomers compared the image to Hubble’s 1997 image (seen below) revealing changes in the nebula on human time scales.
This eerie Hubble image features the center of the Trifid Nebula and the three wing-like bands of thick dust for which the nebula was named. A group of recently formed, massive, bright stars toward the center of the nebula is easily visible. These stars are releasing a flood of ultraviolet radiation that dramatically influences the structure and evolution of the surrounding nebula. Star formation is no longer occurring in the immediate vicinity of this group of bright stars given that their intense radiation has blown away the gas and dust from which recent stars are made.
This 1997 Hubble image taken with Hubble’s Wide Field and Planetary Camera 2 reveals a star-forming cloud of gas and dust in M20 being torn apart by radiation from a massive nearby star, just beyond the top of the frame. Two thin, finger-like jets protrude from the head of a dense cloud in the upper left of the image, which might be forming new stars at their tips.
