About Stars
Stars are enormous spheres of hot plasma powered by nuclear fusion. They are born inside cold clouds of gas and dust, spend most of their lives fusing hydrogen, and eventually change as their fuel supply and internal structure evolve.
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Star Birth
Stars begin inside dense regions of gas and dust.
Learn MoreNuclear Fusion
Stars shine because atomic nuclei combine deep inside them.
Learn MoreStar Colors
A star's color gives clues about its surface temperature.
Learn MoreStar Sizes
Stars range from small red dwarfs to enormous supergiants.
Learn MoreStellar Life Cycles
A star's mass strongly affects how it will age and die.
Learn MoreSupernovae
Some dying stars explode with extraordinary brightness.
Learn MoreStellar Remnants
Dead stars can leave white dwarfs, neutron stars, or black holes.
Learn MoreStars Build Elements
Many atoms in our bodies were forged in stars.
Learn MoreStar Birth
Gravity can cause part of a molecular cloud to collapse. As the material contracts, the center grows hotter and denser until nuclear fusion begins. Young stars may still be surrounded by disks of leftover material that can eventually form planets.
Nuclear Fusion
In a star like the Sun, hydrogen nuclei ultimately combine to form helium. A tiny amount of mass is converted into energy. That energy slowly works its way outward before escaping as light and heat.
Star Colors
Hotter stars often appear blue-white, while cooler stars can look orange or red. The Sun's surface is around 5,500 degrees Celsius and appears white from space. Color is one tool astronomers use to classify stars.
Star Sizes
Red dwarfs are smaller and cooler than the Sun but can burn fuel very slowly for extremely long times. Massive stars are hotter, brighter, and use fuel rapidly. Some evolve into giant or supergiant stars with huge outer layers.
Stellar Life Cycles
Stars similar to the Sun eventually become red giants, shed their outer layers, and leave behind white dwarfs. Much more massive stars can explode as supernovae and leave neutron stars or black holes.
Supernovae
A supernova can briefly shine with the brightness of an entire galaxy. Explosions spread heavy elements into space, enriching gas that can later form new stars, planets, and potentially living things.
Stellar Remnants
White dwarfs are dense cores left by stars like the Sun. Neutron stars are even denser remnants of massive-star explosions. If a collapsing stellar core is massive enough, it can form a black hole.
Stars Build Elements
Fusion inside stars creates elements such as carbon and oxygen. Supernovae and other energetic events create and spread still heavier elements. The calcium in bones and the iron in blood are part of a cosmic story that began long before Earth formed.