Skip to main content Missions Search All NASA MissionsA to Z List of MissionsUpcoming Launches and LandingsSpaceships and RocketsCommunicating with MissionsArtemisJames Webb Space TelescopeHubble Space TelescopeInternational Space StationOSIRIS-RExHumans in Space Why Go to SpaceAstronautsCommercial SpaceDestinationsSpaceships and RocketsLiving in SpaceEarth & Climate Explore Earth ScienceClimate ChangeEarth, Our PlanetEarth Science in ActionEarth MultimediaEarth DataEarth Science ResearchersAbout NASA NASA's ImpactsCenters and FacilitiesDirectoratesOrganizationsPeople of NASACareersInternshipsOur HistoryDoing Business with NASAGet InvolvedContactLearning Resources For Kids and StudentsFor EducatorsFor Colleges and UniversitiesFor ProfessionalsScience for EveryoneSpace Samples for LearningRequest an Exhibit or SpeakerSTEM Engagement at NASAAeronautics Science in the AirNASA AircraftFlight InnovationSupersonic FlightAir Traffic SolutionsGreen Aviation TechDrones & YouTechnology Technology Transfer & SpinoffsSpace Travel TechnologyTechnology Living in SpaceManufacturing and MaterialsRoboticsScience InstrumentsComputingThe Universe ExoplanetsThe Search for Life in the UniverseStarsGalaxiesBlack HolesThe Big BangDark Matter & Dark EnergyThe Solar System The SunMercuryVenusEarthThe MoonMarsJupiterSaturnUranusNeptunePluto & Dwarf PlanetsAsteroids, Comets & MeteorsThe Kuiper BeltThe Oort CloudSkywatchingEspañol CienciaAeronáuticaCiencias TerrestresSistema SolarUniversoScience All NASA ScienceEarth SciencePlanetary ScienceAstrophysics & Space ScienceThe Sun & HeliophysicsBiological & Physical SciencesLunar ScienceCitizen ScienceAstromaterialsAeronautics ResearchHuman Space Travel Research ExploreSearchSubmitNews & EventsMultimediaNASA+
 UniverseCosmic HistoryBuilding BlocksForcesGalaxiesOverviewTypesEvolutionLarge Scale StructuresBlack HolesOverviewTypesAnatomyBlack Hole WeekStarsOverviewTypesMultiple Star SystemsPlanetary SystemsExoplanetsExplorationSensing the UniverseTelescopes 101ObservatoriesMoreNewsDeep DivesQuick ReadsGraphicsGlossaryUniverse HomeExplore This SectionUniverseGalaxiesBlack HolesStarsExoplanetsExplorationMoreUniverse HomeStar BasicsContentsBirthLifeDeathAstronomers estimate that the universe could contain up to one septillion stars – that’s a one followed by 24 zeros. Our Milky Way alone contains more than 100 billion, including our most well-studied star, the Sun.Stars are giant balls of hot gas – mostly hydrogen, with some helium and small amounts of other elements. Every star has its own life cycle, ranging from a few million to trillions of years, and its properties change as it ages.BirthStars form in large clouds of gas and dust called molecular clouds. Molecular clouds range from 1,000 to 10 million times the mass of the Sun and can span as much as hundreds of light-years. Molecular clouds are cold which causes gas to clump, creating high-density pockets. Some of these clumps can collide with each other or collect more matter, strengthening their gravitational force as their mass grows. Eventually, gravity causes some of these clumps to collapse. When this happens, friction causes the material to heat up, which eventually leads to the development of a protostar – a baby star. Batches of stars that have recently formed from molecular clouds are often called stellar clusters, and molecular clouds full of stellar clusters are called stellar nurseries.The edge of a nearby stellar nursery called NGC 3324, found at the northwest corner of the Carina Nebula, forms the “mountains” and “valleys” spanning this image captured by the James Webb Space Telescope.NASA, ESA, CSA, and STScILifeAt first, most of the protostar’s energy comes from heat released by its initial collapse. After millions of years, immense pressures and temperatures in the star’s core squeeze the nuclei of hydrogen atoms together to form helium, a process called nuclear fusion. Nuclear fusion releases energy, which heats the star and prevents it from further collapsing under the force of gravity.A tannish-orange Sun emits swirling pinkish flares slightly south of the middle of the sphereOur Sun, a main sequence star, emits a strong solar flare flashes in this image captured by NASA's Solar Dynamics Observatory.NASA/SDOAstronomers call stars that are stably undergoing nuclear fusion of hydrogen into helium main sequence stars. This is the longest phase of a star’s life. The star’s luminosity, size, and temperature will slowly change over millions or billions of years during this phase. Our Sun is roughly midway through its main sequence stage.A star’s gas provides its fuel, and its mass determines how rapidly it runs through its supply, with lower-mass stars burning longer, dimmer, and cooler than very massive stars. More massive stars must burn fuel at a higher rate to generate the energy that keeps them from collapsing under their own weight. Some low-mass stars will shine for trillions of years – longer than the universe has currently existed – while some massive stars will live for only a few million years.DeathAt the beginning of the end of a star’s life, its core runs out of hydrogen to convert into helium. The energy produced by fusion creates pressure inside the star that balances gravity’s tendency to pull matter together, so the core starts to collapse. But squeezing the core also increases its temperature and pressure, making the star slowly puff up. However, the details of the late stages of the star’s death depend strongly on its mass.A low-mass star’s atmosphere will keep expanding until it becomes a subgiant or giant star while fusion converts helium into carbon in the core. (This will be the fate of our Sun, in several billion years.) Some giants become unstable and pulsate, periodically inflating and ejecting some of their atmospheres. Eventually, all the star’s outer layers blow away, creating an expanding cloud of dust and gas called a planetary nebula.bluish purple image of the Helix NebulaThe Helix nebula, imaged here, lies 650 light-years away in the constellation Aquarius. Also known as NGC 7293, it is a typical example of planetary nebulae.NASA/JPL-CaltechAll that’s left of the star is its core, now called a white dwarf, a roughly Earth-sized stellar cinder that gradually cools over billions of years.A high-mass star goes further. Fusion converts carbon into heavier elements like oxygen, neon, and magnesium, which will become future fuel for the core. For the largest stars, this chain continues until silicon fuses into iron. These processes produce energy that keeps the core from collapsing, but each new fuel buys it less and less time. The whole process takes just a few million years. By the time silicon fuses into iron, the star runs out of fuel in a matter of days. The next step would be fusing iron into some heavier element but doing so requires energy instead of releasing it.colorful image of a supernova remnantThe remnant of a supernova observed in 1572, notably studied by the Danish astronomer Tycho Brahe, lies about 13,000 light-years away in the constellation Cassiopeia. In this composite image, data from NASA’s Chandra X-ray Observatory have been combined with an optical image of stars in the same area.X-ray: NASA/CXC/RIKEN & GSFC/T. Sato et al; Optical: DSSThe star’s iron core collapses until forces between the nuclei push the brakes, then it rebounds. This change creates a shock wave that travels outward through the star. The result is a huge explosion called a supernova. The core survives as an incredibly dense remnant, either a neutron star or a black hole.Material cast into the cosmos by supernovae and other stellar events will enrich future molecular clouds and become incorporated into the next generation of stars.Stars StoriesExplore All Stars StoriesImage Article2 min readHubble Captures a Cosmic FossilArticle2 min readHubble Observes a Cosmic FossilA globular cluster that looks like a very dense, ball-shaped collection of many shining stars in colors of white, yellow-orange, and blue. Some stars appear a bit larger and brighter than others, with the brightest having faint cross-shaped diffraction spikes. The cluster’s stars are scattered mostly uniformly, with their density increasing toward the cluster’s core where they merge into a strong, bright-white glow.5 min readNASA’s Webb Reveals Long-Studied Star Is Actually TwinsArticle2 days ago4 min readComing in Hot — NASA’s Chandra Checks Habitability of ExoplanetsArticle3 days agoAn artist's concept of the binary star system HM Sge on the black background of space sprinkled with various sizes of red and white points of light. At the top of the image a blazing hot white disk surrounds a white dwarf star that is pulling a stream of material from its red giant companion, the glowing mottled ball at bottom right.4 min readHubble Finds Surprises Around a Star That Erupted 40 Years AgoArticle5 days agoKeep ExploringDiscover More Topics From NASAUniverseSplotches of bright-pink and blue-white fill the lower half of the image. A bright bar of white stars extends downward from top-center toward the left. Random areas of dusty clouds form dark streams against the bright backdrop.GalaxiesLooking like a pinwheel, this face-on spiral galaxy holds a bright-white core at image center. Arms curve outward from the core. They hold dark dust lanes and bright star-forming regions. All on a black background dotted with stars.Black HolesExoplanets
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