Have binary stars planets

Over half of all stars belong to double or multiple systems. So far, astronomers suspected that planets could not form, especially in close binary star systems. However, observations with the Spitzer infrared space telescope now show the opposite.

Sunset on a binary star planet

Tucson (USA) - There are just as often dust disks around binary star systems, which indicate the formation of planets, as around single stars. Even more: Such disks are even more common in close binary stars, reports an American research team in the "Astrophysical Journal".

"So a binary star does not seem to be an obstacle to planet formation," says David Trilling of the University of Arizona, the lead author of the study. "So there could be countless planets with more than one sun." Astronomers already knew that there are planets in large double stars where the two stars are more than a thousand times farther apart than the earth is from the sun. Because of the 200 or so planets that have so far been found in other stars, 50 orbit one of the suns of such a wide system. In their observations with the Spitzer telescope, however, Trilling and his colleagues concentrated on systems with distances less than 500 times the distance between the earth and the sun. Because at such distances the influence of the second star should be noticeable.

In the case of narrow systems, however, it is difficult to track down planets using the usual methods. So far there is only one candidate who has not yet been confirmed. Trilling and his colleagues therefore pursued a different strategy. They weren't looking for the planets themselves, but for dust discs around the stars, remnants from the phase of planet formation. In total, the researchers targeted 69 binary stars at distances of 50 to 200 light years. The observations show that 40 percent of these systems have dust discs - almost the same frequency as in single stars. The biggest surprise, according to the scientists, is that in the systems with the smallest distances - less than three times the distance between the earth and the sun - dust disks, at 60 percent, occur significantly more often than in single stars.

"That could mean that planet formation is even more likely with close binary stars than with single stars," says Trilling, "but we need further observations to verify this finding." However, not all double stars are planet-friendly: At mean distances between the stars - between three and 50 times the distance between the earth and the sun - there are significantly fewer dust disks. So planets are obviously preferred for very wide and very narrow double stars.