![]() ![]() The core survives as an incredibly dense remnant, either a neutron star or a black hole. The result is a huge explosion called a supernova. This change creates a shock wave that travels outward through the star. The star’s iron core collapses until forces between the nuclei push the brakes, then it rebounds. The next step would be fusing iron into some heavier element but doing so requires energy instead of releasing it. By the time silicon fuses into iron, the star runs out of fuel in a matter of days. The whole process takes just a few million years. These processes produce energy that keeps the core from collapsing, but each new fuel buys it less and less time. For the largest stars, this chain continues until silicon fuses into iron. Fusion converts carbon into heavier elements like oxygen, neon, and magnesium, which will become future fuel for the core. Sato et al Optical: DSSĪ high-mass star goes further. 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. The 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. Eventually, all the star’s outer layers blow away, creating an expanding cloud of dust and gas called a planetary nebula. (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. However, the details of the late stages of the star’s death depend strongly on its mass.Ī 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. But squeezing the core also increases its temperature and pressure, making the star slowly puff up. 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. DeathĪt the beginning of the end of a star’s life, its core runs out of hydrogen to convert into helium. 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. ![]() More massive stars must burn fuel at a higher rate to generate the energy that keeps them from collapsing under their own weight. Our Sun is roughly midway through its main sequence stage.Ī 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. The star’s luminosity, size, and temperature will slowly change over millions or billions of years during this phase. This is the longest phase of a star’s life. Nuclear fusion releases energy, which heats the star and prevents it from further collapsing under the force of gravity.Īstronomers call stars that are stably undergoing nuclear fusion of hydrogen into helium main sequence stars. 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. Credit: NASA/SDOĪt first, most of the protostar’s energy comes from heat released by its initial collapse. Our Sun, a main sequence star, emits a strong solar flare flashes in this image captured by NASA's Solar Dynamics Observatory. 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. When this happens, friction causes the material to heat up, which eventually leads to the development of a protostar – a baby star. Eventually, gravity causes some of these clumps to collapse. Some of these clumps can collide with each other or collect more matter, strengthening their gravitational force as their mass grows. Molecular clouds are cold which causes gas to clump, creating high-density pockets. ![]() ![]() 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. Stars form in large clouds of gas and dust called molecular clouds. Every star has its own life cycle, ranging from a few million to trillions of years, and its properties change as it ages. Stars are giant balls of hot gas – mostly hydrogen, with some helium and small amounts of other elements. Our Milky Way alone contains more than 100 billion, including our most well-studied star, the Sun. Astronomers estimate that the universe could contain up to one septillion stars – which in numbers is 1,000,000,000,000,000,000,000,000. ![]()
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