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 As a kid growing up in New York City, Rebecca science classes that looked like fun. So he chose Oppenheimer always wanted to study stars and planets. astrophysics, which uses physics to under- stand She never dreamed she would someday discover an how the universe works. Today, he's an entirely new kind of object. In 1995, she observed a small, astrophysicist, studying how stars, planets, and dim object that was neither a planet nor a star. It is called a galaxies form. Since these process take millions of brown dwarf. This observation shows us that there are still years, he models them using computer simulations. things left to be discovered in the universe. Rebecca also Then he compares the models studies faraway planets, and dying stars called white dwarfs. Image credits: © AMNH/D.Finnin; Mordecai-Mark Mac Low: courtesy of AMNH / D. Finnin. 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.

A star is a huge glowing ball of hot gas. Deep inside its core, © AMNH 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?

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 wereThe no Milky stars Way isat the all? galaxy in which our Solar You have to be a really big thinker to imagine System lives. There are more than 200 billion the size of the Universe. It’s so big that light stars in our spiral galaxy, and our Sun is just from the most distant galaxies takes over 10 one of them. Even if you traveled at the speed billion years just to reach us on Earth! That’s of light, it would take you about 1000,000 twice as long as Earth’s been around. Everything years to get across the Milky Way. we’ve ever observed in space is part of our Universe. We don’t know what’s beyond it or if Image credits: The Milky Way in Infrared, there are other Universes out there. courtesy of The COBE Project, DIRBE, and NASA; Mike Shara: courtesy of AMNH. Image credits: The image of the universe © © AMNH American Museum of Natural History and the National Center for Supercomputing In the Milky Way Galaxy alone, there are hundredsApplications, of 1999;billions Charles of Liu: stars. courtesy And of there are many more in the universe. But did you knowAMNH. that a long, long time ago, there 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 Universe. Objects with more mass have greater © AMNH Over 13 billiongravitation yearsal pull ago,than obj thereects with was less m onlyass. Gravity an invisikeeps ble substance called dark matter, along with hydrogen Earth and the planets orbiting around the Sun instead of and heliumflo gas.ating off Dark into sp matter'sace. What would gravity the Univ gatherederse be like this gas to form the first stars. without gravity?

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.

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.

The Earth is our home. So far, it’s the only place that we know of Ninety-three million miles from Earth, a giant ball of hot that has life. Everywhere you look on Earth there is life. This is gas brightens the sky. Nuclear reactions in the Sun’s core possible because Earth has lots of water. It’s also just the right create energy, which gradually flows to the Sun’s distance from the Sun. Some people call Earth the “Goldilocks surface. This energy reaches Earth in the form of planet.” It’s not too hot (like Venus), and not too cold (like Mars), sunlight. The Sun’s heat and light warm Earth’s surface, it’s just right! drive weather and currents, and make life possible on our planet. We experience the Sun’s energy every time Image credits: courtesy of NASA; Rosamond Kinzler: AMNH. we feel its warmth on our skin or see with the aid of sunlight.

Image credits: courtesy of NASA; Neil Tyson: 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.

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 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 © AMNH 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.

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.

Scientists observe stars using telescopes on Earth and in space. They see stars being born, maturing, and at the end of their lives.

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 The Orion constellation is known for having some of the brightest with amazement and dreamed of a closer look. The invention of the stars in the night sky. On a clear night, try to find the three stars that telescope in 1608 gave humans their chance to explore the vastness form the “belt” of the hunter. Above and below the belt you’ll see of the Universe. In fact, most of what we know about the Universe Betelgeuse and Rigel. Betelgeuse looks reddish and Rigel is blue. The comes from studying the sky with telescopes. Telescopes use lenses cloudy area just below the belt is the Orion Nebula – the closest and mirrors to gather light and produce images. Galileo was the major star-forming region to Earth. first to use telescopes for astronomy. Image credits: "Observers", "Institute", Sven Kohle and Till Credner. Image credits: courtesy of AMNH.

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 © AMNH 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.

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.

The Pleiades is an older star cluster than the one in Orion. Young stars are leaving this cluster, too.

Scientists also observe stars at the ends of their lives. The remains of one of these stars formed the Helix Nebula.

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.

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.