In this image of the planetary nebula IC 5148, the white dwarf that created the nebula is so hot it looks blue-white. White dwarfs are very hot at first, but over billions of years they cool off until they become black dwarfs and no longer shine. What’s left of the star becomes a small white dwarf at the nebula’s center. Its outer layers blow away into space one at a time over about 10,000 years and become a planetary nebula. In stars up to one and a half times more massive than the Sun, the star’s core eventually runs out of helium to fuse into carbon. The biggest stars turn into black holes-spheres of matter so dense that not even light can escape their gravity. Most stars run out of fuel and become white dwarfs, but a few generate massive explosions so big they can be seen with the naked eye. How Stars DieĪlthough all stars are born the same way, how they die depends on their size. Hot stars glow blue-white or white, cooler stars glow orange or yellow, and the coolest stars are red, which is why these giants give off a red glow. Eventually the star reaches 15 million degrees Fahrenheit, so hot that the hydrogen atoms in its core begin fusing into helium.Īt the center of this image, a protostar in the Orion Nebula is heating clouds of gas as it gobbles them up.īecause red giants are so big, they have a much larger surface area to radiate away the energy from all the fusion going on inside them. A protostar starts off looking like a cloud, but as gravity pulls it tighter and tighter together, it heats up and begins to glow. Protostars are huge clumps of gas and dust that aren’t quite hot enough to achieve fusion in their core. Over long periods of time, they draw so much gas to themselves that they become round and condense into a protostar. Because the gravity of any object, including a ball of hydrogen, grows as it gets bigger, those clumps start attracting more and more gas. Within nebulas, gravity pulls clumps of hydrogen together. Stars form inside nebulas because nebulas contain lots of hydrogen, the gas stars are mostly made of. In the image of the Orion Nebula above, the red stars in the lower-left corner are baby stars. Formed when a dying star explodes or when the swirling motion of a galaxy creates a concentration of interstellar gases, they are some of the most breathtaking, and famous, parts of the universe. Others glow because the gas inside them gives off light, or starlight reflects off or passes through them.
Some are dark shapes that blot out the light behind them like ghostly monsters. Nebulas-huge clouds of gas between the stars-take many forms. Cooling off and expansion as a red giant.
Star formation in a cosmic nursery known as a nebula.Every star begins life by moving through four stages:
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