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In Pictures: Journey to the Stars This text is provided courtesy of OLogy, the American Museum of Natural History’s website for kids. Hi, we're Mordecai-Mark Mac Low and Rebecca Oppenheimer. We are astrophysicists at the American Museum of Natural History. Did you know that stars are really important to us? In fact, they make all life possible. Let's find out why! In college, Mordecai-Mark Mac Low decided to take science classes that looked like fun. So he chose astrophysics, which uses physics to under- stand how the universe works. Today, he's an astrophysicist, studying how stars, planets, and galaxies form. Since these process take millions of years, he models them using computer simulations. Then he compares the models Image credits:© AMNH/D.Finnin; Mordecai-Mark Mac Low: courtesy of AMNH /D. Finnin. As a kid growing up in New York City, Rebecca Oppenheimer always wanted to study stars and planets. She never dreamed she would someday discover an entirely new kind of object. In 1995, she observed a small, dim object that was neither a planet nor a star. It is called a brown dwarf. This observation shows us that there are still things left to be discovered in the universe. Rebecca also studies faraway planets, and dying stars called white dwarfs. Image credits: courtesy of AMNH / D. Finnin. Twinkle, twinkle, little star... On a clear night, we can see thousands of stars with our naked eye. © AMNH A star is a huge glowing ball of hot gas. Deep inside its core, hydrogen atoms smash together, forming helium and releasing huge amounts of energy that heats the gas. This is called nuclear fusion, and it’s why a star shines. As the hot gas pushed outward, it opposes the inward pull of gravity. This balance of forces is what makes a star, a star. It holds the star together and keeps it at a steady temperature for most of its life. Image credits: © AMNH; Mordecai-Mark Mac Low: courtesy of AMNH / D. Finnin. In the Milky Way Galaxy alone, there are hundreds of billions of stars. And there are many more in the universe. But did you know that a long, long time ago, there were no stars at all? © AMNH In the Milky Way Galaxy alone, there are hundreds of billions of stars. And there are many more in the universe. But did you know that a long, long time ago, there You have to be a really big thinker to imagine Theno Milky Way is galaxy in which our Solar were stars attheall? System lives. There are more than 200 billion stars in our spiral galaxy, and our Sun is just one of them. Even if you traveled at the speed of light, it would take you about 1000,000 years to get across the Milky Way. Image credits: The Milky Way in Infrared, courtesy of The COBE Project, DIRBE, and NASA; Mike Shara: courtesy of AMNH. the size of the Universe. It’s so big that light from the most distant galaxies takes over 10 billion years just to reach us on Earth! That’s twice as long as Earth’s been around. Everything we’ve ever observed in space is part of our Universe. We don’t know what’s beyond it or if there are other Universes out there. Image credits: The image of the universe © American Museum of Natural History and the National Center for Supercomputing In the Milky Way Galaxy alone, there are hundreds of 1999; billions ofLiu:stars. And Applications, Charles courtesy of there AMNH. are many more in the universe. But did you know that a long, long time ago, there © AMNH were no stars at all? Over 13 billion years ago, there was only an invisible substance called dark matter, along with hydrogen and helium gas. Dark matter's gravity gathered this gas to form the first stars. In the Milky Way Galaxy alone, there are hundreds of billions of stars. And there are many more in the universe. But did you know that a long, long time ago, there were no stars at all? Gravity is the force of attraction between all objects in the © AMNH Universe. Objects with more mass have greater gravitational pull than objects with less mass. Gravity keeps Over 13 billion years ago, there was only an invisible substance called dark matter, Earth and the planets orbiting around the Sun instead of and heliumfloating gas.offDark matter's gravity gathered into space. What would the Universe be like this gas to form the first stars. without gravity? along with hydrogen Over 13 billion years ago, there was only an invisible substance called dark matter, along with hydrogen But the first stars didn't last long. They were massive. They burned hot, lived fast, and died young. They blew up in gigantic explosions called supernovas. Ninety-three million miles from Earth, a giant ball of hot gas brightens the sky. Nuclear reactions in the Sun’s core create energy, which gradually flows to the Sun’s surface. This energy reaches Earth in the form of sunlight. The Sun’s heat and light warm Earth’s surface, drive weather and currents, and make life possible on our planet. We experience the Sun’s energy every time we feel its warmth on our skin or see with the aid of sunlight. The Earth is our home. So far, it’s the only place that we know of that has life. Everywhere you look on Earth there is life. This is possible because Earth has lots of water. It’s also just the right distance from the Sun. Some people call Earth the “Goldilocks planet.” It’s not too hot (like Venus), and not too cold (like Mars), it’s just right! Image credits: courtesy of NASA; Rosamond Kinzler: AMNH. Image credits: courtesy of NASA; Neil Tyson: AMNH. © AMNH Stars are factories for new elements. As stars live and die, they form almost all of the elements that we know of, like oxygen and carbon. We see light every day -- whether from light bulbs, flames, flashlights, or the Sun (our most important source of light). We see objects because they reflect, or bounce, light into our eyes. Light is a form of energy called electromagnetic radiation. It's made of tiny particles called photons that travel in straight lines. In a vacuum, nothing can travel faster. Image credits: Eric Hamilton. Earth orbits a star we call the Sun. It is a middle-aged yellow star that is more massive than the average star. © AMNH © AMNH The Sun is a star that powers our planet. It brightens our days and provides us with heat and other forms of energy. © AMNH The Sun is a star that powers our planet. It brightens our days and provides us with heat and other forms of energy. The Sun, like all the stars, is a huge glowing ball of hot gas. It gives off energy as light that we can see-sunshine. It also gives off invisible light, such as ultraviolet and radio. Energy is the ability to do work. Scientists define "work" as when a force moves something. When you lift a brick, you are doing work because you are exerting a force to lift the heavy object.Energy comes in many forms, such as heat, sound, light, electric, and chemical. Energy easily changes from one form to another. Image credits: Eric Hamilton. © AMNH At the end of its life, the Sun will become a red giant. It will blow its outer layers out into the universe, seeding new stars and planets. But don’t worry. This won’t happen for 5 billion years. © AMNH Scientists observe stars using telescopes on Earth and in space. They see stars being born, maturing, and at the end of their lives. © AMNH This is the Orion Nebula. Huge stellar nurseries like this are found all over the Milky Way and other spiral galaxies. Before telescopes were invented, people gazed at the night sky with amazement and dreamed of a closer look. The invention of the telescope in 1608 gave humans their chance to explore the vastness of the Universe. In fact, most of what we know about the Universe comes from studying the sky with telescopes. Telescopes use lenses and mirrors to gather light and produce images. Galileo was the first to use telescopes for astronomy. Image credits: courtesy of AMNH. The Orion constellation is known for having some of the brightest stars in the night sky. On a clear night, try to find the three stars that form the “belt” of the hunter. Above and below the belt you’ll see Betelgeuse and Rigel. Betelgeuse looks reddish and Rigel is blue. The cloudy area just below the belt is the Orion Nebula – the closest major star-forming region to Earth. Image credits: "Observers", "Institute", Sven Kohle and Till Credner. A galaxy is a giant, spinning object made of gas, dust, and stars held together by gravity. Galaxies come in different shapes and sizes and can contain billions of stars. Most occur in groups that are also held together by gravity. We now know that the Universe has billions of galaxies, and the Milky Way is only one of them. © AMNH Image credits: The Southern Pinwheel Galaxy from VLT, FORS Team 8.2-meter VLT ESO Hubble Deep Field ,R. Williams and the HDF Team (STScI) and NASA M31: The Andromeda Galaxy, © and Courtesy of Jason Ware; Charles Liu: courtesy of AMNH. See those teardrop shapes? They are gas and dust clouds that cradle infant stars. Most stars form in tightly packed groups called star clusters. © AMNH The Pleiades is an older star cluster than the one in Orion. Young stars are leaving this cluster, too. © AMNH Scientists also observe stars at the ends of their lives. The remains of one of these stars formed the Helix Nebula. © AMNH All that remains of the star is a very dense object called a white dwarf. It will take billions of years to cool and slowly fade away. © AMNH Brown dwarfs are neither stars nor planets. And they are as numerous as stars! The discovery of these new objects tells us that our cosmic family is more diverse than we imagined.