The University Record, January 16, 1996
Orion Nebula: cloud of gas is nursery for infant stars
The constellation of Orion, the Giant Hunter, sparkles in Michigan's winter evening sky. At the midpoint of his sword, which is marked by three stars hanging from his belt, observers can see the Orion Nebula---a glowing cloud of gases where astronomers using the Hubble Space Telescope recently found hundreds of new stars being formed.
"Surrounding many of the new stars are dark, swirling disks of material where new planetary systems may be forming," says astronomer Richard Teske. "This discovery is the best evidence yet that planets form by the same processes that make stars, and it strengthens arguments that planets must exist throughout the universe."
Observers who view the constellation of Orion are looking toward a vast region about 1,500 light-years away where an immense amount of gaseous and dusty material floats in space between the stars. The dust motes in this area are much smaller than dust grains blowing across Earth's deserts and beaches. Yet enormous quantities collect together with atoms and molecules of gases to form clouds measuring many light-years across. Scientists believe the force of gravity gathers these huge clouds of gases and dust together to make groups of stars. The clouds' own gravity acting over a time span of millions of years gradually condenses them, squeezing gas and dust together until hot shining stars are formed.
"If this is truly Nature's method of making stars, it is probably an imperfect one," Teske says. "Astronomers believe that a lot of the star-forming material is left behind in the swirling cloud or disk surrounding the new star. Planets form later from this leftover material. Most scientists believe this is how the sun and planets in our solar system formed long ago. The Space Telescope's discoveries in the Orion Nebula are a stunning confirmation of this broad brush picture. About 150 of the 700 newly-formed stars observed there are accompanied by disks containing enough leftover material to make planets."
Nebulae like the one visible in Orion are huge glowing gas clouds extending across many light-years of space. The gas atoms that compose the clouds are stimulated to emit light when the ultraviolet radiation of nearby stars energizes them, causing the gas to emit its own light. In Orion, a quartet of stars at the middle of the sword causes gas in space surrounding the stars to glow with a foggy luminescence. This iridescent region 15 light-years wide marks the place where the Hubble Telescope discovered the new stars and their associated disks, according to Teske.
"Viewed with the naked eye, the Orion Nebula looks like a fuzzy star. Binoculars show its greenish shape, and a small telescope reveals it still more clearly," says Teske. "The green light is produced when oxygen atoms in the gas emit their characteristic green wavelengths."
A chemical analysis of the distant nebula's gases was made years ago by astronomers who studied the wavelengths of the light that shines from it. "They concluded that most of the 92 natural chemical elements are present in the Orion star-forming region in a mixture similar to the familiar chemical blend found in our sun and its planets," Teske says. "So planets formed there would be made of substances similar to the planets in our own solar system. It is possible that Earth-like objects could exist as companions to stars in the Orion Nebula, too."