These catastrophic bursts leave behind a small core that may become a neutron star or even, if the remnant is massive enough, a black hole.īecause certain supernovae have a predictable pattern of destruction and resulting luminosity, astronomers are able to use them as “standard candles,” or astronomical measuring tools, to help them measure distances in the universe and calculate its rate of expansion. While they may appear to be swelling red giants on the outside, their cores are actually contracting, eventually becoming so dense that they collapse, causing the star to explode. Massive stars eschew this evolutionary path and instead go out with a bang-detonating as supernovae. At this point, which scientists have yet to observe, they become known as black dwarfs. Eventually all white dwarfs go dark and cease producing energy. Some, if they exist as part of a binary star system, may gather excess matter from their companion stars until their surfaces explode, triggering a bright nova. The red giant phase is actually a prelude to a star shedding its outer layers and becoming a small, dense body called a white dwarf. But there are different ways a star’s life can end, and its fate depends on how massive the star is. These large, swelling stars are known as red giants. Helium sinks to the star's core and raises the star's temperature-causing its outer shell of hot gases to expand. Now around 4.6 billion years old, Earth’s sun is considered an average-size yellow dwarf star, and astronomers predict it will remain in its main sequence stage for several billion more years.Īs stars move toward the ends of their lives, much of their hydrogen has been converted to helium. Stars spend 90 percent of their lives in their main sequence phase. Supergiants may have radii a thousand times larger than that of our own sun. Along with main sequence and white dwarf stars, other groups include dwarfs, giants, and supergiants. Hot stars appear white or blue, whereas cooler stars appear to have orange or red hues.īy plotting these and other variables on a graph called the Hertzsprung-Russell diagram, astronomers can classify stars into groups. Color can also vary from star to star because their temperatures are not all the same. Their brightness is a factor of how much energy they put out–known as luminosity–and how far away from Earth they are. Some stars shine more brightly than others. This process emits an enormous amount of energy, keeping the star hot and shining brightly. They exist in a stable state of nuclear fusion, converting hydrogen to helium and radiating x-rays. Most of the stars in our galaxy, including the sun, are categorized as main sequence stars. Millions of years later, when the core temperature climbs to about 27 million degrees Fahrenheit (15 million degrees Celsius), nuclear fusion begins, igniting the core and setting off the next-and longest-stage of a star’s life, known as its main sequence. Increasing pressure creates rising temperatures, and during this time, a star enters what is known as the relatively brief T Tauri phase. Because the dust in the nebulae obscures them, protostars can be difficult for astronomers to detect.Īs a protostar gets smaller, it spins faster because of the conservation of angular momentum-the same principle that causes a spinning ice skater to accelerate when she pulls in her arms. One of these contracting masses of gas, known as a protostar, represents a star’s nascent phase. Over the course of thousands of years, gravity causes pockets of dense matter inside the nebula to collapse under their own weight. As a general rule, the more massive the star, the shorter its life span.īirth takes place inside hydrogen-based dust clouds called nebulae. The life cycle of a star spans billions of years. It’s impossible to know how many stars exist, but astronomers estimate that in our Milky Way galaxy alone, there are about 300 billion. They are the building blocks of galaxies, of which there are billions in the universe. Aside from our sun, the dots of light we see in the sky are all light-years from Earth. Stars are huge celestial bodies made mostly of hydrogen and helium that produce light and heat from the churning nuclear forges inside their cores. A correct, albeit less soothing, rendition might be: Emit, emit, gigantic ball of gas.
Gently singing Twinkle, twinkle, little star may lull a baby to sleep, but beyond the confines of Earth’s atmosphere, the words aren’t exactly accurate.
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