National Aeronautics and Space Administration The Helix Nebula: What is it? The object shown on the front of this poster is the This “Mountains Helix Nebula. Although this object and others like it are of Creation” image called planetary nebulae (pronounced NEB-u-lee), they was captured by really have nothing to do with planets. They got their name the Spitzer Space ZKHQDVWURQRPHUV¿rst saw them through early telescopes, Telescope in infrared because they looked similar to planets with rings around light. It reveals them, like Saturn. billowing mountains of dust ablaze with A planetary nebula is the ¿res of active star really a shell of glowing gas formation. GALEX and plasma from a star at the can see the new stars end of its life. The star has forming, because they glow brightly in ultraviolet (UV) light. blown off much of its material However, the surrounding dust and gas clouds are cooler and and what is left is a very not so visible to GALEX. compact object called a white dwarf. For a while, the white dwarf is still hot and bright A Tug of War enough to make the material Planetary nebula JnEr1, A star is an amazing from the former star glow, as seen by GALEX. ! Ow! If not for balancing act between two ! * * gravity, my head and that is what we see as a * * would explode! beautiful nebula. Over 10,000 huge forces. On the one * years or so, the gas will drift away and the white dwarf will hand, the crushing force of the star’s own gravity Gravity Heat cool so much that we can no longer see the nebula. Gravity tries to squeeze the stellar Pressure This is what will happen to our Sun in about 5 billion material into the smallest years. What do you suppose our Sun’s nebula will look and tightest ball possible. like to some distant alien astronomers? But on the other hand, the force of the tremendous To understand what res burning at the star’s happens to a star at the end KHDWDQGSUHVVXUHIURPWKHQXFOHDU¿ center tries to push all that material outward. of its life, we need to know something about the rest of a When the star has used up almost all of its hydrogen star’s life, from birth, through nuclear fuel (after several billion years), the outward middle-age (our Sun’s stage pressure from the nuclear reactions is no longer able to of life now), and into its last counteract the gravity, and the core of the star collapses stage of life. under its own weight, so to speak. As the core collapses, it gets even hotter. The outer layers of the star puff up from Planetary nebula A21, as this increased heat, but as the star puffs up, the outer layers seen by GALEX. get cooler. The star is called a red giant at this point. Our own Sun will become a red giant before it dies in How Does a Star Form? about 5 billion years. It will be so large at this stage in its Stars are born where there are thick clouds of gas life that it will engulf the orbits of Mercury and Venus and (mostly hydrogen) and dust in space. Gravitational maybe even Earth. Even if Earth remains outside the Sun, attraction makes these materials clump together. The the oceans and the atmosphere will have boiled away and “clumped” object grows more and more massive as more nothing will be able to live on what will be a burnt cinder and more gas gets pulled in by the growing gravitational of rock. force. As the object becomes more massive, squeezed by But even as the outer layers puff up, the core of a red tremendous gravitational forces, it becomes more dense giant continues to contract and get even hotter. When the (compact). As it gets denser, it gets hotter and hotter. FRUHJHWVKRWHQRXJKWKHQXFOHDU¿res are once again lit, as Eventually, if the giant gas ball gets massive enough and the helium atoms fuse into carbon and oxygen atoms. It dense enough, the atoms of hydrogen gas will begin to is in the cores of dying stars that much of the carbon and fuse together, creating helium atoms and igniting the oxygen atoms in ours bodies were made! QXFOHDU¿res that make it a star. EW-2006-07-026-JPL 1 National Aeronautics and Space Administration Clues from Ancient Light This activity introduces some important The same thing happens to starlight. The galaxies science concepts in simple language. The puzzle are all moving away from us and each other because space itself is expanding. As the light waves move through activity reinforces one aspect. Participants cut out expanding space, they get stretched out. The longer the the squares on the second page with the pictures light waves’ journey through space, the more stretched out of objects of different “ages,” then rearrange they become. Astronomers say this stretched out light is them from oldest to youngest. A third page shows “red-shifted.” the pictures in the right order (allowing room for differing interpretation in a couple of cases), How Old Is the Starlight? explaining a little about each picture. If desired, the puzzle page may be photocopied and glued to GALEX sees starlight that has been traveling for just card stock or a manila folder before cutting out the a few years from stars that are “only” a few tens of trillions squares. of kilometers away. But it also sees really stretched out “red-shifted” starlight that has been traveling over 10 billion years! That is more than two-thirds of the age of the whole universe! So GALEX is seeing faraway galaxies GALEX Looks Back in Time as they were a very long time ago when they gave off the light, as well as nearby galaxies as they looked just a few Like all telescopes that see far into space, GALEX hundred thousand years ago. is a time machine. As it peers into the distance, it is also peering into the past. That is because the light that GALEX Just as old photographs show how people looked detects has taken a long time to travel from its source (a decades ago, GALEX sees pictures of galaxies when the galaxy, for example) to reach GALEX. Although light universe was much younger than now. So astronomers travels faster than anything else (300,000 kilometers or can look at the galaxy pictures from far away—and long 186,000 miles per second, in round numbers), it does not ago—compare them with pictures of galaxies nearby—very WUDYHOLQ¿nitely fast. That means, while light travels, time recent—and see how galaxies and their stars are born, age, passes. The farther it travels, the more time passes. and die over time. They can learn how galaxies evolve. The distance light can travel in one Earth year is called a light year. A light year is a very long distance: How Old Do I Look? around 9 trillion kilometers (6 trillion miles). Can you tell how old something is just by looking at it? The squares on the next page contain pictures of Light travels in waves, similar to the way water waves old things, new things, and every age in between things. move through the ocean or sound waves move through Cut out the squares. For each row (A – F) of six pictures the air1H[WWLPHD¿re truck approaches with its siren from a single category, like nature or animals, arrange the blasting, listen closely. You will notice that the siren’s note objects by age, oldest on the left, youngest on the right. deepens a little just as the truck passes you. The note is Some things may be a little hard to compare, but make a lower because the sound waves are being stretched as the good guess anyway. At least be able to explain why your truck continues to move away from you. arrangement by age could be right! Compare your best guesses to ours on the answer page. light wave Space expanding STAR EARTH over time stretches light waves traveling through it. Light travels in waves, just as energy traveling through the ocean pushes the water into waves. But as light waves travel through space, they gradually get stretched out. That is because, along with the universe, space itself is expanding and stretching the distances between things. EW-2006-07-026-JPL 3 National Aeronautics and Space Administration CUT OUT SQUARES. IN EACH ROW, ARRANGE OLDEST TO NEWEST (LEFT TO RIGHT). A: Nature A: Nature A: Nature A: Nature A: Nature A: Nature Earth Tree Galaxy Bee hive Mountain Flower B: Animals/ B: Animals B: Animals B: Animals B: Animals B: Animals Baby Butterfly Milk cow Old man Giant tortoise Baby bird C: Transportation C: Transportation C: Transportation C: Transportation C: Transportation C: Transportation Pegasus rocket Wright (launched GALEX brothers’ Volkswagen space telescope) Covered wagon First metal bike Viking ship airplane Beetle D: Communication D: Communication D: Communication D: Communication D: Communication D: Communication Telephone Telephone Telephone (separate ear & (combined ear & GALEX ground (rotary dial) Cell phone mouth pieces) mouth pieces) station antenna Smoke signals E: Gone quickly E: Gone quickly E: Gone quickly E: Gone quickly E: Gone quickly E: Gone quickly Birthday candle Cloud Soap bubble flame Flower Lightning Leaf F: “Imagers” F: “Imagers” F: “Imagers” F: “Imagers” F: “Imagers” F: “Imagers” GALEX space Isaac Newton’s 35-millimeter telescope Box camera Telescope film camera Digital camera Cave painting EW-2006-07-026-JPL 4 National Aeronautics and Space Administration ANSWERS! A A A A A A Mountains can be This galaxy, M81, Trees can be This beehive is almost as old as is over 10 billion hundreds of years likely to be at least This daffodil looks Earth itself.