37 Nebulae-Mid

Nebulae FOCUS Question What is the relationship between nebulae and stars?

What Is a Nebula? The universe is made of billions of galaxies—groups of thousands to trillions of stars held together by the force of gravity. Dust and gas are scattered in the space between the stars. A nebula forms when some of the dust and gas clumps together into a cloud-like formation. Emission nebulae form around stars. The stars heat up the gas and dust so much that the nebulae give off their own light. A stellar remnant nebula is a special type of emission nebula Stellar remnant nebulae. form when a dying star blows off layers of gas. The gas is so hot that it emits its own light. This type of nebula is also called a planetary nebula because it is shaped like a planet. Word Wise The plural form of nebula is nebulae (NEB-yoo-lee).

Reflection nebulae are cooler than emission nebulae and do not give off their own light. Instead, they reflect the light from nearby stars. Unlike other types of nebulae, absorption nebulae do not look much like clouds. They neither emit nor reflect light. Instead, they absorb light. They appear as black regions in space. Nebulae are mostly made of the gases hydrogen and helium. About 90 percent of a nebula is hydrogen, and 9 percent is helium. There are smaller amounts of other elements such as oxygen, carbon, and nitrogen. In fact, nebulae have the same mix of elements as stars. Astronomers now know that nebulae are made of materials that came from ancient stars.

If you look into a clear, dark sky, you might be able to see some nebulae without a telescope. The Orion Nebula, for example, is visible in the constellation Orion. Most nebulae are hard to distinguish from stars, however. To learn much about them, we need telescopes. Some telescopes allow us to observe the visible light energy coming from nebulae. We can learn what nebulae are made of by observing their visible light, but nebulae also give off other types of energy that we cannot see. These forms of light energy include infrared, ultraviolet, X-rays, and gamma rays. Studying different types of light that nebulae emit and reflect helps us understand them. The Hubble Space Telescope (HST), which has been orbiting Earth since 1990, has recorded infrared, visible light, and ultraviolet pictures from space. With the HST, we learned that dust and gas of the Orion Nebula is heated by thousands of stars.

This image of the Eskimo Nebula was made using the Chandra X-Ray Observatory, a space telescope. The pink parts of this image are "false color." The light is not actually pink; it represents the light from X-rays. All of the other colors are the actual colors that we can see with our eyes. The Spitzer Space Telescope observes infrared light. The colors in the image below represent different wavelengths of infrared light. The dark parts of the image are not giving off any infrared light. They are dense, cold, dark regions of sooty dust.

Star Nurseries When astronomers first began studying nebulae, all they could see were fuzzy regions in space. Today, using powerful telescopes, scientists can see nebulae more clearly. They have discovered that many nebulae are star nurseries—places where new stars are forming. Because gravity pulls matter together, over time the gas and dust of a nebula begin to collapse. Clumps of material come together. The gravitational pull increases, and clumps of particles move faster. As the particles move faster and faster, they become hotter. and hotter When the clumps get big enough and have enough energy, they become hot, glowing stars. Word Wise The word nebula comes from the Latin word for mist or clouds. The word nebulous comes from the same root. Something that is nebulous is very unclear or vague.