Related: Amazing photos of supernova explosions So is Antares, the brightest star in the constellation Scorpius. Betelgeuse, which forms the shoulder of the constellation Orion (The Hunter), is a red supergiant. Some of the brightest and best-known stars in the night sky are red supergiants. And they march through the other late-life steps even faster than that. For example, while our sun will end up fusing hydrogen in its core for about 10 billion years, stars that become red supergiants exhaust their reserves in just 10 million years or so. When it's all said and done, these massive stars leave behind either a neutron star or a black hole.Īnd this all happens quite quickly, cosmically speaking, because huge stars burn through their fuel very fast. Their cores get hot enough to burn carbon, which our sun never will, and they eventually die in powerful supernova explosions. Stars roughly eight to 40 times more massive than the sun, for example, go through a "red supergiant" phase. The end-of-life scenario for giant stars is different. This fate awaits many other stars as well - all of them that are less than about eight times more massive than the sun, in fact. (The misleading name was given by early astronomers, who thought these sky sights looked like planets.) These shells are much larger and fainter than their parent stars.Īfter spending about 1 billion years as a red giant, our own sun will become a white dwarf, packing most of its initial mass into a sphere roughly the size of Earth. Around the time of this transition, the star ejects its outer layers in huge clouds of gas and dust known as planetary nebulae. The star eventually becomes incredibly compact, turning into a superdense object known as a white dwarf. This ignition causes the giant's outer layers to expand even further, but its core continues to collapse in on itself. The core shrinks again and a helium shell just beyond it ignites, as happened with hydrogen shortly after the star burned through its stores of that initial fuel. But for less hefty stars, it occurs with an explosive flash.Įventually, the helium in the core runs out and fusion stops. (This is known as the " triple alpha process" because it involves three helium-4 isotopes, or alpha particles.) If the star is at least 2.2 times more massive than our sun, helium-to-carbon ignition is a relatively gradual process. Red giants' core temperatures, however, continue to rise as the core contracts further, eventually reaching levels where helium fuses to form carbon. This temperature change causes stars to shine in the redder part of the spectrum, leading to the name "red giant," though they are often more orangish in appearance. Because these stars' energy is spread across such a large area, their surface temperatures are actually relatively cool, reaching only 4,000 to 5,800 degrees Fahrenheit (2,200 to 3,200 degrees Celsius), a little over half as hot as the sun. Red giant stars bloat to 62 million to 620 million miles in diameter (100 million to 1 billion kilometers) - 100 to 1,000 times wider than our sun is today. "This causes the star to expand enormously and increase in luminosity - the star becomes a red giant." "Meanwhile, the helium core continues to contract and increase in temperature, which leads to an increased energy generation rate in the hydrogen shell," the explainer continues. "This raises the internal temperature of the star and ignites a shell of hydrogen burning around the inert core," Swinburne University of Technology in Australia wrote in a stellar evolution explainer.
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