Most of the stars in the Milky Way have companion stars. They travel through the galaxy together, bound by their mutual gravity. But many of those companions are quite remote — they can be separated by thousands of times the distance between Earth and the Sun.
The system with the widest separation yet seen is Fomalhaut. Its main star, now known as Fomalhaut A, is quite bright. Tonight, it rises to the lower right of the Moon, and is directly below the Moon around midnight.
For a long time, it looked like Fomalhaut was like the Sun — a single star. In recent years, though, astronomers have discovered that it has two companions. But they’re a long way from the bright star. In fact, the whole system spans more than three light-years.
Fomalhaut A is almost twice as big and heavy as the Sun, and about 17 times brighter.
Its closer companion is Fomalhaut B. It’s a little smaller and less massive than the Sun. It’s not visible to the eye alone, even though the system is just 25 light-years away.
The farther companion is Fomalhaut C. It’s so far from A that astronomers didn’t suspect that the two stars were related. But a study in 2013 showed that the stars are the same age, and they move through space in tandem. In other words, they’re companions.
Star C is a red dwarf — a bare cosmic ember. And it’s in the hinterlands of the Fomalhaut system — so far out that the star takes at least 20 million years to orbit its bright sibling.
Script by Damond Benningfield