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 (opens in new tab)' 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 (opens in new tab).

Red giant colorista