The Eagle Nebula

When we look in the direction of the constellation Sagittarius, we look at a crowded inner arm of our galaxy's spiral across a vast stretch of nearly empty space. In that arm is a cloud of gas and dust called the Eagle Nebula. The Eagle Nebula is about 7000 light years from us, and gets as wide as 70 light years. That means the nebula is 70,000 times the width of our solar system!

A long time ago, the most concentrated parts of the nebula collapsed to form stars. The stars are in a cluster near the middle of the cloud. Their radiation has carved out a hole, and we are seeing into it. The stars are ionizing the surrounding gas, so we see its pink glow behind the cluster. Around the edges, we also see dark clouds of dust and gas curving around and blocking some of the glowing wall. Those clouds are lit up too, of course, but not on our side.

The densest remaining pockets of gas are resisting the radiation pressure, and protecting pillars of gas behind them. Astronomers believe that each dense pocket is collapsing to form a new star. Images taken in infrared light revealed that a supernova explosion occurred in the cluster about 1000 years ago, and the expanding shock wave is nearing the tips of the pillars. When it reaches them, they will be torn apart, and as the gas is concentrated on the edge of the shock wave, more stars will form. (The reason we know so much about these pillars is that they have been subjects of study by the Hubble and Spitzer Space Telescopes.)

The star cluster in the Eagle Nebula has the more formal name of NGC 6611, and the nebula itself is IC 4703. The whole thing is also known as Messier Object 16, or simply M16.