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Double Orange

July 26, 2016

Billions of years from now, our Sun will puff up to become an orange giant, shining hundreds or thousands of times brighter than it does now.

Orange giants are rare, but they’re so bright that they’re easy to see in the night sky. There’s one in the Big Dipper, for example, and the bright stars Arcturus, Aldebaran, and Pollux are orange giants as well.

Astronomers recently discovered a double orange giant in Sagittarius. The constellation is low in the south-southeast as night falls, and its brightest stars outline the shape of a teapot.

The recently discovered orange giants orbit each other once every nine months. They’re slightly farther apart than Mars is from the Sun. Each star is about five times as massive as the Sun. One of them is about 50 times the Sun’s diameter, while the other is even bigger.

The stars’ sizes and temperatures reveal how much light they emit into space. Comparing this with how bright they look indicates that they’re 7,000 light-years from Earth.

The two stars are much younger than the Sun — only about a hundred million years old. But because they’re so massive, they evolved quickly. They’ve converted the hydrogen in their cores into helium. Now, they’re converting the helium into carbon and oxygen — something the Sun won’t do for billions of years.

The details on these colorful stellar giants will yield new insights into the many orange giants that speckle the night sky.

Script by Ken Croswell

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