According to modern theories, every object in the Universe today started out as a cloud of gas. These nebulae are building blocks, and using things like gravity and fusion, go on to create all the stars and planets, black holes, galaxies, globular clusters, and everything else in the cosmos.
Where to Find It
The zodiac sign Sagittarius is a centaur, raising up his bow ready to fire. Located between Ophiuchus and Capricornus, Sagittarius contains the center of the Milky Way galaxy. Slightly up and to the right of his bow sits a tiny smudge of light, faintly visible to the naked eye. That tiny smudge is the Lagoon Nebula, a cloud of gas measuring 110 light years across. Estimates put the Lagoon Nebula between 4,000 and 6,000 light years away from the Earth.
Even though the nebula is visible to the naked eye, it is still very faint. For this reason ancient astronomers weren't aware of its existence. It was discovered in 1747 by Guillaume Le Gentil. The nebula itself is composed mostly of hydrogen, and is classified as an emission nebula and an H II region. Many of the stars inside the Lagoon Nebula give off huge amounts of energy. This energy is put into the surrounding gas, causing it to ionize. We are able to see the nebula because the ionized gas that it is composed of gives off its own light.
What's on the Inside
Inside the Lagoon Nebula astronomers are finding some very interesting structures. O-type stars are some of the rarest stars in the Universe. They are the biggest stars in our classification system, and are mostly hidden inside nebulae. These enormous stars have such strong gravity that fusion going on in their cores happens orders of magnitude faster than other stars. Where most stars last billions of years, O-type stars live brilliantly short lives measured in millions of years, putting out huge amounts of energy. One of these O-type stars in the nebula is responsible for a tornado-like structure that can be seen in the image to the right.
The Lagoon Nebula also contains a number of what astronomers call Bok globules. These lightyear-wide globs of dust and gas are protostellar material, meaning that they are in the process of collapsing into a star. The nebula also has several Herbig-Haro objects. Young stars can often be very temperamental. Gravity is not always completely balanced with the explosive force of fusion from its core. This lack of hydrostatic equilibrium sometimes causes enormous jets of material to be ejected from the poles of a star, extending for light years in either direction. We can observe these Herbig-Haro objects when these extremely energetic streams of matter slam into the surrounding gas and dust.
Facts About the Lagoon Nebula
Distance: 4,1000 light years
Radius: 55 x 20 light years
Apparent Magnitude: 6.0
Apparent Dimensions: 90 x 40 arcmins
Right Ascension: 18h 03m 37s
Declination: −24° 23′ 12″