Our solitary sunsets here on Earth might not be all that common in the
grand scheme of things. New observations from NASA's Spitzer Space
Telescope have revealed that mature planetary systems -- dusty disks of
asteroids, comets and possibly planets -- are more frequent around
close-knit twin, or binary, stars than single stars like our sun. That
means sunsets like the one portrayed in this artist's photo concept, and
more famously in the movie "Star Wars," might be quite commonplace in the
universe.
Binary and multiple-star systems are about twice as abundant as
single-star systems in our galaxy, and, in theory, other galaxies. In a
typical binary system, two stars of roughly similar masses twirl around
each other like pair-figure skaters. In some systems, the two stars are
very far apart and barely interact with each other. In other cases, the
stellar twins are intricately linked, whipping around each other quickly
due to the force of gravity.
Astronomers have discovered dozens of planets that orbit around a single
member of a very wide stellar duo. Sunsets from these worlds would look
like our own, and the second sun would just look like a bright star in the
night sky.
But do planets exist in the tighter systems, where two suns would dip
below a planet's horizon one by one? Unveiling planets in these systems is
tricky, so astronomers used Spitzer to look for disks of swirling
planetary debris instead. These disks are made of asteroids, comets and
possibly planets. The rocky material in them bangs together and kicks up
dust that Spitzer's infrared eyes can see. Our own solar system is
swaddled in a similar type of disk.
Surprisingly, Spitzer found more debris disks around the tightest binaries
it studied (about 20 stars) than in a comparable sample of single stars.
About 60 percent of the tight binaries had disks, while the single stars
only had about 20 percent. These snug binary systems are as close or
closer than just three times the distance between Earth and the sun. And
the disks in these systems were found to circumnavigate both members of
the star pair, rather than just one.
Though follow-up studies are needed, the results could mean that planet
formation is more common around extra-tight binary stars than single
stars. Since these types of systems would experience double sunsets, the
artistic view portrayed here might not be fiction.
The original sunset photo used in this artist's concept was taken by
Robert Hurt of the Spitzer Science Center at the California Institute of
Technology, Pasadena, Calif.