Photograph by Mondolithic
Read Caption
The star HR 5171 A is orbited by another, much smaller, sun.
Photograph by Mondolithic

Gigantic Double Sun

Get the facts on the star HR 5171 A and its sister sun.

The star outside your spaceship’s windshield is a spectacular sight. HR 5171 A is a fireball 1,300 times larger than the Earth’s sun. It’s so big that if it were in our sun’s position, it would swallow up Earth beneath its 10,000°F surface. To look at it from your spaceship, you have to wear special goggles—this star is almost a million times brighter than our sun.

As you watch HR 5171 A burn, you notice something strange. An object is peeking over the horizon, growing larger and larger. It’s another sun—a smaller one that orbits the giant HR 5171 A. This small sun (though it’s still about 350 times larger than Earth’s sun) is snuggled up so close to its sister sun that they’re touching.

Even though it’s tiny compared to the giant HR 5171 A, the smaller sun has much stronger surface gravity. As it circles, it sucks hot, bright gas off of the larger star. The sister suns are enveloped in a big disk of swirling gas.

You fly in close to get a better look. Whoa! Your spaceship is blown backward by a gust of powerful wind. Magnetic fields are erupting from HR 5171 A, sending waves of a hot, electrically charged fluid called plasma shooting off its surface.

You glance down to see that the numbers on your instrument panel are flickering. The plasma is frying your electronics. You rev the engine and speed away before it’s too late.