Red Giant

The core of the aging star shrinks. As it does, the gravitational energy released raises the temperature in the hydrogen-burning shell, increasing the pace of fusion. With this increase, more and more energy is dumped into the outer layers of the star, increasing the outward pressure. So while the core shrinks, the outer layers of the star expand dramatically, cooling as they do. As this happens, the star becomes more luminous and cooler, moving to the upper right-hand side of the H-R diagram (see Chapter 17). The resulting star is a called a red giant. For a solar mass main sequence star, a red giant will be about 100 times larger than the sun, with a core that is a mere ^a» the size of the star.

Star Words

A red giant is a late stage in the career of stars about as massive as the sun. More massive stars in their giant phase are referred to as supergiants. Their relatively low surface temperature produces their red color.

Star Words

A red giant is a late stage in the career of stars about as massive as the sun. More massive stars in their giant phase are referred to as supergiants. Their relatively low surface temperature produces their red color.

Close Encounter

The night sky offers many examples of red giants. Two of the most impressive are Aldebaran, the brightest star in the constellation Taurus, and Arcturus, in Bootes. Look to the constellation Orion for an example of a red supergiant, Betelgeuse (pronounced Beetlejuice). You'll find very large array image of Betelgeuse in Chapter 17.

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