Young stars hide in far constellation

The Hubble space telescope has produced a remarkable collection of striking images during its years in orbit, none more so that this view of a small segment of the Omega Nebula.

It was released late last month to mark the 13th anniversary of Hubble's launch on April 24th, 1990.

Also known as the Swan or, Horseshoe Nebula and in the southern hemisphere the Lobster Nebula, its official name is far less prosaic, simply Diffuse Nebula M17 (NGC6618). It is a hotbed of star formation located about 5,500 light years away in the constellation Sagittarius.

While it may look something like a tortured seacoast lashed by pounding waves, the image actually shows an ocean of glowing hydrogen gas, backlit by bright young stars. The view seen here is about three light-years across.

The cloud is actually a mixture and their colours can identify the gases present. Red represents sulphur and green is hydrogen. Blue denotes the presence of oxygen.

The wave-like patterns seen in the gas are both sculpted and illuminated by a torrent of ultraviolet radiation beaming out from the massive young stars. These lie just outside the picture to the upper left of the image.

The glow of these patterns accentuates the true three-dimensional structure of the gases, according to Hubble's operators. The ultraviolet radiation is carving and heating the surfaces of cold hydrogen gas clouds. The warmed surfaces glow orange and red in this photograph.

The intense heat and pressure cause some material to stream away from those surfaces, creating the glowing veil of even hotter greenish gas that masks background structures. The pressure on the tips of the waves may trigger new star formation within them.

The nebula is unusual in that the powerful young stars are hidden within the clouds, about 35 of them. The high-energy radiation coming from them however causes excitation and light emission amongst the gas species present in the clouds.

Astronomers believe star formation is either still active or only just completed in this nebula. It also contains a large amount of dark material that blocks the view but which can be seen glowing brightly in the infrared range after being heated up by the stars.

An estimate of the mass of gas in the entire nebula is about 800 times the mass of the sun. This would be enough to produce a substantial cluster of stars. The full nebula including bright central material and the lower luminosity material around the fringes is apparently 40 light years across.