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!
Twinkle, twinkle, little star... On a clear night, we can see thousands of stars
with our naked eye.
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?
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.
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.
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, like all 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.
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 ends of their lives.
This is the Orion Nebula.
Huge stellar nurseries like this are found all over the Milky Way and other spiral galaxies.
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.