Betelgeuses elusive co-star left a trail of clues for astronomers

For more than a century, Betelgeuse has looked like a star with a secret.

It swells and fades on a six-year rhythm that never quite made sense. The star, about 650 light-years away in space, is old, bloated, and unstable, but not unstable enough to explain its slow pulse. 

The answer might be simpler than expected. Betelgeuse, pronounced "Beetlejuice" just like the Tim Burton film, appears to have company, traveling within its own atmosphere.

Astronomers have previously speculated that the red supergiant...