Nebulae, interstellar clouds of dust, molecules, hydrogen, helium and other ionized gases where new stars are being born, are among the most visually impressive objects in the night sky. Although they come in different shapes and colors, many share a common characteristic: when observed for the first time, their odd and evocative shapes trigger astronomers’ imaginations and lead to curious names. Thus the Seagull Nebula moniker. It has also been called Sh 2-292, RCW 2 and Gum 1, all for various reasons.
The Seagull Nebula lies just on the border between the constellations of Monoceros (The Unicorn) and Canis Major (The Great Dog) and is close to Sirius, the brightest star in the night sky. The nebula lies more than four hundred times further away than the famous star. A new image from the Wide Field Imager shows the head part of the Seagull Nebula, part of the larger nebula known more formally as IC 2177 which is spread out over 100 light-years and resembles a seagull in flight. This cloud of gas and dust is located about 3,700 light-years away from Earth. The entire bird shows up best in wide-field images.
Close-up of the Seagull Nebula. Credit: ESO
The complex of gas and dust that forms the head of the seagull glows brightly in the sky due to the strong ultraviolet radiation coming mostly from one brilliant young star — HD 53367 — that can be spotted in the center of the image and could be taken to be the seagull’s eye. HD 53367 is a young star with twenty times the mass of our Sun and classified as a Be star, a type of B star with prominent hydrogen emission lines in its spectrum. This star has a five solar mass companion in a highly elliptical orbit.
The radiation from the young stars causes the surrounding hydrogen gas to glow with a rich red colour and become an HII region, so named because they consist of ionized hydrogen (H) in which the electrons are no longer bound to protons. HI is the term used for un-ionized, or neutral, hydrogen. The red glow from HII regions occurs because the protons and electrons recombine and in the process emit energy at certain well-defined wavelengths or colors. One such prominent transition (called hydrogen alpha, or H-alpha) leads to the strong red color.
Light from the hot blue-white stars is also scattered off the tiny dust particles in the nebula to create a contrasting blue haze in some parts of the picture.
A broad view of the Milky Way before closing in on the familiar bright star Sirius and the nearby constellation of Orion (The Hunter). There is a faint red object resembling a bird in flight, the Seagull Nebula (IC 2177), and then it zooms in on what turns out to be a dramatic star formation region. The final view of the head part of the seagull is a new detailed image from the Wide Field Imager on the MPG/ESO 2.2-meter telescope. Credit: ESO/Digitized Sky Survey 2/Nick Risinger (skysurvey.org). Music: Disasterpeace
Although a small bright clump in the Seagull Nebula complex was observed for the first time by the German-British astronomer Sir William Herschel back in 1785, the part shown here had to await photographic discovery about a century later.
This nebula lies close in the sky to the Thor’s Helmet Nebula (NGC 2359), which was the winner of ESO’s recent Choose what the VLT Observes contest. This nebula, with its distinctive shape and unusual name, was picked as the first ever object selected by members of the public to be observed by ESO’s Very Large Telescope. These observations are going to be part of the celebrations on the day of ESO’s 50th anniversary October 5th 2012.